Ultraviolet

Ultraviolet

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Ultraviolet light is electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...

 with a wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

 shorter than that of visible light, but longer than X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

s, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV. It is named because the spectrum consists of electromagnetic waves with frequencies higher than those that humans identify as the color violet.

Although ultraviolet radiation is invisible to the human eye, most people are aware of the effects of UV through sunburn
Sunburn
A sunburn is a burn to living tissue, such as skin, which is produced by overexposure to ultraviolet radiation, commonly from the sun's rays. Usual mild symptoms in humans and other animals include red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV...

,and in tanning beds. The UV spectrum has many other effects, both beneficial and damaging, to human health.

UV light is found in sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

 and is emitted by electric arcs and specialized lights such as black light
Black light
A black light, also referred to as a UV light, ultraviolet light, or Wood's lamp, is a lamp that emits ultraviolet radiation in the long-wave range, and little visible light...

s. It can cause chemical reactions, and causes many substances to glow or fluoresce
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...

. Most ultraviolet is classified as non-ionizing radiation
Non-ionizing radiation
Non-ionizing radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules—that is, to completely remove an electron from an atom or molecule...

. The higher energies of the ultraviolet spectrum from about 150 nm ('vacuum' ultraviolet) are ionizing
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...

, but this type of ultraviolet is not very penetrating and is blocked by air.

Discovery


The discovery of UV radiation was associated with the observation that silver salts
Silver halide
A silver halide is one of the compounds formed between silver and one of the halogens — silver bromide , chloride , iodide , and three forms of silver fluorides. As a group, they are often referred to as the silver halides, and are often given the pseudo-chemical notation AgX...

 darken when exposed to sunlight. In 1801, the German physicist Johann Wilhelm Ritter
Johann Wilhelm Ritter
Johann Wilhelm Ritter was a German chemist, physicist and philosopher. He was born in Samitz near Haynau in Silesia , and died in Munich.-Life and work:...

 made the hallmark observation that invisible rays just beyond the violet end of the visible spectrum were especially effective at lightening silver chloride
Silver chloride
Silver chloride is a chemical compound with the chemical formula AgCl. This white crystalline solid is well known for its low solubility in water . Upon illumination or heating, silver chloride converts to silver , which is signalled by greyish or purplish coloration to some samples...

-soaked paper. He called them "oxidizing rays" to emphasize chemical reactivity and to distinguish them from "heat rays" at the other end of the visible spectrum. The simpler term "chemical rays" was adopted shortly thereafter, and it remained popular throughout the 19th century. The terms chemical and heat rays were eventually dropped in favour of ultraviolet and infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...

, respectively.

The discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet because it is strongly absorbed by air, was made in 1893 by the German physicist Victor Schumann
Victor Schumann
Victor Schumann was a physicist and spectroscopist who in 1893 discovered the vacuum ultraviolet.He was the first to measure spectra below 200 nm. For this, he used a prism and lenses in fluorin instead of quartz, he prepared himself photographic plates with a reduced layer of gelatin, and he...

.

Origin of the term


The name means "beyond violet" (from Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 ultra, "beyond"), violet being the color
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...

 of the shortest wavelengths of visible light. UV light has a shorter wavelength than violet light.


The electromagnetic spectrum of ultraviolet light can be subdivided in a number of ways. The draft ISO standard on determining solar irradiances (ISO-DIS-21348) describes the following ranges:
Name Abbreviation Wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

 range in nanometers
Energy per photon
Before UV spectrum Visible light above 400 nm below 3.10 eV
Ultraviolet A, long wave, or black light
Black light
A black light, also referred to as a UV light, ultraviolet light, or Wood's lamp, is a lamp that emits ultraviolet radiation in the long-wave range, and little visible light...

UVA 400 nm–315 nm 3.10–3.94 eV
Near NUV 400 nm–300 nm 3.10–4.13 eV
Ultraviolet B or medium wave UVB 315 nm–280 nm 3.94–4.43 eV
Middle MUV 300 nm–200 nm 4.13–6.20 eV
Ultraviolet C, short wave, or germicidal
Ultraviolet germicidal irradiation
Ultraviolet germicidal irradiation is a sterilization method that uses ultraviolet light at sufficiently short wavelength to kill microorganisms. It is used in a variety of applications, such as food, air and water purification. UV has been a known mutagen at the cellular level for more than...

UVC 280 nm–100 nm 4.43–12.4 eV
Far FUV 200 nm–122 nm 6.20–10.2 eV
Vacuum VUV 200 nm–100 nm 6.20–12.4 eV
Low LUV 100 nm–88 nm 12.4–14.1 eV
Super SUV 150 nm–10 nm 8.28–124 eV
Extreme EUV
Extreme ultraviolet
Extreme Ultraviolet radiation is high-energy ultraviolet radiation, generally defined to be electromagnetic radiation in the part of the electromagnetic spectrum spanning wavelengths from 120 nm down to 10 nm, and therefore having photons with energies from 10 eV up to 124 eV...

121 nm–10 nm 10.2–124 eV
Beyond UV range X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

s
below 10 nm above 124 eV


In photolithography
Photolithography
Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate...

 and laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

 technology, the term deep ultraviolet or DUV refers to wavelengths below 300 nm.
Extreme Ultraviolet stands here for discrete spectral ranges of around 13.5 nm (in future planned also 6.x nm) of about 2 % bandwidth.
In fields like analytics and life sciences, the acronym "XUV" is used for Extreme Ultraviolet for characterizing the broader spectral range, such as to distinguish from EUV. XUV is separated from x-rays and VUV, by the fact that the photoelectron ionization of innershell electrons is the - by orders of magnitudes - dominating photon-matter interaction effect. This is in contrast to x-rays, where scatter is relevant and VUV where the interaction is mainly with outer ("chemical active") electrons of the atoms and molecules.

"Vacuum UV" is so named because it is absorbed strongly by air and is, therefore, used in a vacuum
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...

. In the long-wave limit of this region, roughly 150–200 nm, the principal absorber is the oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 in air. Work in this region can be performed in an oxygen-free atmosphere, pure nitrogen being commonly used, which avoids the need for a vacuum chamber.

See 1 E-7 m
1 E-7 m
To help compare different orders of magnitude this page lists lengths between 10−7 and 10−6 m .Distances shorter than 100 nm*100 nm — greatest particle size that can fit through a surgical mask...

 for a list of objects of comparable sizes.

Natural sources of UV


The sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 emits ultraviolet radiation in the UVA, UVB, and UVC bands. The Earth's ozone layer
Ozone layer
The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone . This layer absorbs 97–99% of the Sun's high frequency ultraviolet light, which is potentially damaging to the life forms on Earth...

 blocks 97-99% of this UV radiation from penetrating through the atmosphere.
Of the ultraviolet radiation that reaches the Earth's surface, 98.7% is UVA. (UVC and more energetic radiation is responsible for the generation of the ozone layer, and formation of the ozone there). Extremely hot stars emit proportionally more UV radiation than the sun; the star R136a1
R136a1
R136a1 is a blue hypergiant star and the most massive star known. It is an estimated 265 solar masses. The star is also the most luminous at 8,700,000 times the luminosity of the Sun....

 has a thermal energy of 4.57 eV, which falls in the near-UV range.

Ordinary glass is partially transparent
Transparency and translucency
In the field of optics, transparency is the physical property of allowing light to pass through a material; translucency only allows light to pass through diffusely. The opposite property is opacity...

 to UVA but is opaque
Opacity (optics)
Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc...

 to shorter wavelengths, whereas silica or quartz glass
Fused quartz
Fused quartz and fused silica are types of glass containing primarily silica in amorphous form. They are manufactured using several different processes...

, depending on quality, can be transparent even to vacuum UV wavelengths. Ordinary window glass passes about 90% of the light above 350 nm, but blocks over 90% of the light below 300 nm.

Vacuum UV, which begins at 200 nm, can of course propagate through a vacuum—hence the name—but air is opaque to it, as these wavelengths are strongly absorbed by molecular oxygen in the air. Pure nitrogen (with less than about 10 ppm oxygen) is transparent to wavelengths in the range of about 150–200 nm. This has come to have wide practical significance since semiconductor manufacturing processes have been using wavelengths shorter than 200 nm. By working in oxygen-free gas, the equipment does not have to be built to withstand the pressure differences required to work in a vacuum. Some other scientific instruments which operate in this spectral region, such as circular dichroism
Circular dichroism
Circular dichroism refers to the differential absorption of left and right circularly polarized light. This phenomenon was discovered by Jean-Baptiste Biot, Augustin Fresnel, and Aimé Cotton in the first half of the 19th century. It is exhibited in the absorption bands of optically active chiral...

 spectrometers, are also commonly nitrogen-purged.

Extreme UV is characterized by a transition in the physics of interaction with matter: wavelengths longer than about 30 nm interact mainly with the chemical valence electrons of matter, whereas shorter wavelengths interact mainly with inner-shell electrons and nuclei. The long end of the EUV/XUV spectrum is set by a prominent He+
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

 spectral line
Spectral line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from a deficiency or excess of photons in a narrow frequency range, compared with the nearby frequencies.- Types of line spectra :...

 at 30.4 nm. XUV is strongly absorbed by most known materials, but it is possible to synthesize multilayer optics that reflect up to about 50% of XUV radiation at normal incidence. This technology, which was pioneered by the NIXT
NIXT
The NIXT, or Normal Incidence X-ray Telescope, was a sounding rocket payload flown in the 1990s by Professor Leon Golub of the Smithsonian Astrophysical Observatory, to prototype normal-incidence optical designs in extreme ultraviolet solar imaging...

 and MSSTA
MSSTA
The Multi-spectral solar telescope array, or MSSTA, was a sounding rocket payload built by Professor A.B.C. Walker, Jr. at Stanford University in the 1990s to test EUV/XUV imaging of the Sun using normal incidence EUV-reflective multilayer optics...

 sounding rockets in the 1990s, has been used to make telescopes for solar imaging
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 (current examples are SOHO
Solar and Heliospheric Observatory
The Solar and Heliospheric Observatory is a spacecraft built by a European industrial consortium led by Matra Marconi Space that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December 2, 1995 to study the Sun, and has discovered over 2100 comets. It began normal operations in May...

/EIT and TRACE
TRACE
TRACE was a NASA space telescope designed to investigate the connections between fine-scale magnetic fields and the associated plasma structures on the Sun by providing high resolution images and observation of the solar photosphere and transition region to the corona...

), and equipment for nanolithography
Nanolithography
Nanolithography is the branch of nanotechnology concerned with the study and application of fabricating nanometer-scale structures, meaning patterns with at least one lateral dimension between the size of an individual atom and approximately 100 nm...

 (printing of very small-scale traces and devices on microchips
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

).

"Black lights"


A black light, Wood's light, or UV light is a lamp that emits long-wave UV radiation and very little visible light. Fluorescent black lights are typically made in the same fashion as normal fluorescent lights, except that a different phosphor
Phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...

 is used on the inside of the tube which emits UV instead of visible light, and the clear glass envelope of the bulb may be replaced by a deep-bluish-purple glass called Wood's glass
Wood's glass
Wood's glass is an optical filter glass invented by American physicist Robert Williams Wood which allows ultraviolet and infrared light to pass through while blocking most visible light. It was developed as a light filter used in communications during World War I...

, a nickel-oxide–doped glass, which blocks almost all visible light above 400 nanometres. The color of such lamps is often referred to in the lighting industry as "blacklight blue" or "BLB", to distinguish them from UV lamps used in "bug zapper
Bug zapper
A bug zapper, or more formally an electrical discharge insect control system is a device that attracts and kills flying insects that are attracted by light. A light source attracts insects to an electrical grid, where they are electrocuted by touching two wires with a high voltage between them...

" insect traps, that do not have the blue Wood's glass. These are designated "blacklight" ("BL") lamps. The phosphor typically used for a near 368 to 371 nanometre emission peak is either europium
Europium
Europium is a chemical element with the symbol Eu and atomic number 63. It is named after the continent of Europe. It is a moderately hard silvery metal which readily oxidizes in air and water...

-doped strontium fluoroborate (SrB4O7F:Eu2+) or europium-doped strontium borate (SrB4O7:Eu2+) while the phosphor used to produce a peak around 350 to 353 nanometres is lead-doped barium silicate (BaSi2O5:Pb+). "Blacklight Blue" lamps peak at 365 nm.

While "black lights" do produce light in the UV range, their spectrum is confined to the long-wave UVA region. Unlike UVB and UVC, which are responsible for the direct DNA damage that leads to skin cancer, black light is limited to lower-energy, longer waves and does not cause sunburn, although it can damage collagen fibers and destroy vitamins A and D in skin.

A black light may also be formed, very inefficiently, by simply using Wood's glass instead of clear glass as the envelope for a common incandescent bulb. This was the method used to create the very first black light sources. Though cheaper than the fluorescent source, only 0.1% of the input power is converted to usable radiation, as the incandescent light radiates as a black body
Black body
A black body is an idealized physical body that absorbs all incident electromagnetic radiation. Because of this perfect absorptivity at all wavelengths, a black body is also the best possible emitter of thermal radiation, which it radiates incandescently in a characteristic, continuous spectrum...

 with very little emission in the UV. Incandescent bulbs used to generate significant UV, due to their inefficiency, may become dangerously hot. More rarely still, high-power (hundreds of watts) mercury-vapor black lights that use a UV-emitting phosphor and an envelope of Wood's glass are made, are used mainly for theatrical and concert displays. They also become very hot during normal use.

Some UV fluorescent bulbs specifically designed to attract insects use the same near-UV emitting phosphor as normal blacklights, but use plain glass instead of the more expensive Wood's glass. Plain glass blocks less of the visible mercury emission spectrum, making them appear light-blue to the naked eye. These lamps are referred to as "blacklight" or "BL" in most lighting catalogs.

Ultraviolet fluorescent lamps


Fluorescent lamps without a phosphorescent coating to convert UV to visible light, emit ultraviolet light with two peaks at 253.7 nm and 185 nm due to the peak emission of the mercury within the bulb. Eighty-five to ninety percent of the UV produced by these lamps is at 253.7 nm, while only five to ten percent is at 185 nm. Germicidal lamps use quartz (glass) doped with an additive to block the 185 nm wavelength. With the addition of a suitable phosphor
Phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...

 (phosphorescent coating) , they can be modified to produce a UVA, UVB, or visible light spectrum (all fluorescent tubes used for domestic and commercial lighting are mercury (Hg) UV emission bulbs at heart).

Such low-pressure mercury lamps are used extensively for disinfection, and in standard form have an optimum operating temperature
Operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...

 of about 30 degrees Celsius. Use of a mercury amalgam allows operating temperature to rise to 100 degrees Celsius, and UVC emission to about double or triple per unit of light-arc length. These low-pressure lamps have a typical efficiency of approximately thirty to thirty-five percent, meaning that for every 100 watts of electricity consumed by the lamp, it will produce approximately 30-35 watts of total UV output. UVA/UVB emitting bulbs also sold for other special purposes, such as reptile-keeping.

Ultraviolet LEDs


Light-emitting diodes (LEDs) can be manufactured to emit light in the ultraviolet range, although practical LED arrays are very limited below 365 nm. LED efficiency at 365 nm is about 5-8%, whereas efficiency at 395 nm is closer to 20%, and power outputs at these longer UV wavelengths are also better. Such LED arrays are beginning to be used for UV curing applications, and are already successful in digital print applications and inert UV curing environments. Power densities approaching 3,000 mW/cm2 (30 kW/m2) are now possible, and this, coupled with recent developments by photoinitiator and resin formulators, makes the expansion of LED-cured UV materials likely.

Ultraviolet lasers


UV laser diode
Laser diode
The laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode. The most common type of laser diode is formed from a p-n junction and powered by injected electric current...

s and UV solid-state laser
Solid-state laser
A solid-state laser is a laser that uses a gain medium that is a solid, rather than a liquid such as in dye lasers or a gas as in gas lasers. Semiconductor-based lasers are also in the solid state, but are generally considered as a separate class from solid-state lasers .-Solid-state...

s can be manufactured to emit light in the ultraviolet range. Wavelengths available include 262, 266, 349, 351, 355, and 375 nm. Ultraviolet lasers have applications in industry (laser engraving
Laser engraving
Laser engraving, or laser marking, is the practice of using lasers to engrave or mark an object. The technique does not involve the use of inks, nor does it involve tool bits which contact the engraving surface and wear out...

), medicine (dermatology
Dermatology
Dermatology is the branch of medicine dealing with the skin and its diseases, a unique specialty with both medical and surgical aspects. A dermatologist takes care of diseases, in the widest sense, and some cosmetic problems of the skin, scalp, hair, and nails....

 and keratectomy), secure communications, and computing (optical storage
Optical storage
Optical storage is a term from engineering referring to the storage of data on an optically readable medium. Data is recorded by making marks in a pattern that can be read back with the aid of light, usually a beam of laser light precisely focused on a spinning disc. An older example, that does...

). They can be made by applying frequency conversion to lower-frequency lasers, or from Ce:LiSAF crystals (cerium
Cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight...

 doped
Dopant
A dopant, also called a doping agent, is a trace impurity element that is inserted into a substance in order to alter the electrical properties or the optical properties of the substance. In the case of crystalline substances, the atoms of the dopant very commonly take the place of elements that...

 with lithium strontium aluminum fluoride), a process developed in the 1990s at Lawrence Livermore National Laboratory
Lawrence Livermore National Laboratory
The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...

.

Gas-discharge lamps



Argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

 and deuterium
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

 lamps are often used as stable sources, either windowless or with various windows such as magnesium fluoride
Magnesium fluoride
Magnesium fluoride is an inorganic compound with the formula MgF2. The compound is a white crystalline salt and is transparent over a wide range of wavelengths, with commercial uses in optics.-Production and structure:...

.

Detecting and measuring UV radiation


Ultraviolet detection and measurement technology can vary with the part of the spectrum under consideration. While some silicon detectors are used across the spectrum, and in fact the US NIST has characterized simple silicon diodes that work with visible light too, many specializations are possible for different applications. Many approaches seek to adapt visible light-sensing technologies, but these can suffer from unwanted response to visible light and various instabilities. A variety of solid-state and vacuum devices have been explored for use in different parts of the UV spectrum.
Ultraviolet light can be detected by suitable photodiode
Photodiode
A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.The common, traditional solar cell used to generateelectric solar power is a large area photodiode....

s and photocathode
Photocathode
A photocathode is a negatively charged electrode in a light detection device such as a photomultiplier or phototube that is coated with a photosensitive compound...

s, which can be tailored to be sensitive to different parts of the UV spectrum.
Sensitive ultraviolet photomultiplier
Photomultiplier
Photomultiplier tubes , members of the class of vacuum tubes, and more specifically phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum...

s are available.

Vacuum UV


Technology for VUV instrumentation has been largely driven by solar physics for many decades and more recently some photolithography
Photolithography
Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate...

 applications for semiconductors. While optics can be used to remove unwanted visible light that contaminates the VUV, in general, detectors can be limited by their response to non-VUV radiation, and the development of "solar-blind" devices has been an important area of research. Wide-gap solid-state devices or vacuum devices with high-cutoff photocathodes can be attractive compared to silicon diodes. Recently, a diamond-based device flew on the LYRA
LYRA
LYRA is the solar UV radiometer on board Proba-2, a European Space Agency technology demonstration satellite that was launched on November 2, 2009....

 (see also Marchywka Effect
Marchywka Effect
The Marchywka Effect refers to electrochemical cleaning of diamond using an electric field induced with remote electrodes.-Discovery and development:...

).

Human health-related effects of UV radiation



The health effects ultraviolet radiation has on human health has implications on weighting the risks and benefits of sun exposure
Risks and benefits of sun exposure
The ultraviolet radiation in sunlight, though a principal source of vitamin D3 compared to diet, is mutagenic. Supplementing diet with vitamin D3 supplies vitamin D without this mutagenic effect, but bypasses natural mechanisms that would prevent overdoses of vitamin D generated internally from...

, but is also implicated in issues such as fluorescent lamps and health
Fluorescent lamps and health
Fluorescent lamps have been suggested to have an impact on human health in various ways.-Time:Nocturnal exposure to light in the short wavelength ranges generated by some fluorescent lamps may interfere with mammalian circadian rhythms due to its suppressing effect on melatonin production...

.

Vitamin D



UVB exposure induces the production of vitamin D
Vitamin D
Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....

 in the skin at a rate of up to 1,000 IUs per minute. The majority of positive health effects are related to this vitamin. It has regulatory roles in calcium metabolism (which is vital for normal functioning of the nervous system, as well as for bone growth and maintenance of bone density), immunity, cell proliferation, insulin
Insulin
Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....

 secretion, and blood pressure.

Aesthetics


Too little UVB radiation may lead to a lack of vitamin D. Too much UVB radiation may lead to direct DNA damage
Direct DNA damage
Direct DNA damage can occur when DNA directly absorbs the UV-B-photon. UVB light causes thymine base pairs next to each other in genetic sequences to bond together into thymine dimers, a disruption in the strand, which reproductive enzymes cannot copy...

, sunburn, and skin cancer. An appropriate amount of UVB (which varies according to skin color
Human skin color
Human skin color is primarily due to the presence of melanin in the skin. Skin color ranges from almost black to white with a pinkish tinge due to blood vessels underneath. Variation in natural skin color is mainly due to genetics, although the evolutionary causes are not completely certain...

) leads to a limited amount of direct DNA damage. This is recognized and repaired by the body, then melanin production is increased, which leads to a long-lasting tan. This tan occurs with a 2-day lag phase after irradiation.

Medical applications


Ultraviolet radiation has other medical applications, in the treatment of skin conditions such as psoriasis
Psoriasis
Psoriasis is an autoimmune disease that appears on the skin. It occurs when the immune system mistakes the skin cells as a pathogen, and sends out faulty signals that speed up the growth cycle of skin cells. Psoriasis is not contagious. However, psoriasis has been linked to an increased risk of...

 and vitiligo
Vitiligo
Vitiligo is a condition that causes depigmentation of sections of skin. It occurs when melanocytes, the cells responsible for skin pigmentation, die or are unable to function. The cause of vitiligo is unknown, but research suggests that it may arise from autoimmune, genetic, oxidative stress,...

. UVA radiation has been much used in conjunction with psoralens (PUVA
PUVA
PUVA is a psoralen + UVA treatment for eczema, psoriasis, graft-versus-host disease and vitiligo, and mycosis fungoides. The psoralen is applied or taken orally to sensitize the skin, then the skin is exposed to UVA. Long term use has been associated with higher rates of skin cancer.Psoralens are...

 treatment) for psoriasis, although this treatment is less used now because the combination produces dramatic increases in skin cancer, and because treatment with UVB radiation by itself is more effective. In cases of psoriasis and vitiligo, UV light with wavelength of 311 nm is most effective.

Harmful effects


An overexposure to UVB radiation can cause sunburn
Sunburn
A sunburn is a burn to living tissue, such as skin, which is produced by overexposure to ultraviolet radiation, commonly from the sun's rays. Usual mild symptoms in humans and other animals include red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV...

 and some forms of skin cancer. However the most deadly form - malignant melanoma - is mostly caused by the indirect DNA damage
Indirect DNA damage
Indirect DNA damage occurs when a UV-photon is absorbed in the human skin by a chromophore that does not have the ability to convert the energy into harmless heat very quickly. Molecules that do not have this ability have a long lived excited state. This long lifetime leads to a high probability...

 (free radicals and oxidative stress). This can be seen from the absence of a UV-signature mutation in 92% of all melanoma. In humans, prolonged exposure to solar UV radiation may result in acute and chronic health effect
Health effect
Health effects are changes in health resulting from exposure to a source. Health effects are an important consideration in many areas, such as hygiene, pollution studies, workplace safety, nutrition and health sciences in general...

s on the skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...

, eye, and immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...

. Moreover, UVC can cause adverse affects that can variously be mutagenic or carcinogenic.

UVC rays are the highest energy, most dangerous type of ultraviolet light. Little attention has been given to UVC rays in the past since they are filtered out by the atmosphere. However, their use in equipment such as pond sterilization
Sterilization (microbiology)
Sterilization is a term referring to any process that eliminates or kills all forms of microbial life, including transmissible agents present on a surface, contained in a fluid, in medication, or in a compound such as biological culture media...

 units may pose an exposure risk, if the lamp is switched on outside of its enclosed pond sterilization unit.

On April 13, 2011 the International Agency for Research on Cancer of the World Health Organization classified all categories and wavelengths of Ultraviolet Radiation as a Group 1 carcinogen. This is the highest level designation for carcinogens and means "There is enough evidence to conclude that it can cause cancer in humans".
Cancer risk


UVA, UVB, and UVC can all damage collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...

 fibers and, therefore, accelerate aging of the skin. Both UVA and UVB destroy vitamin A in skin, which may cause further damage.
In the past, UVA was considered less harmful, but today it is known it can contribute to skin cancer via indirect DNA damage
Indirect DNA damage
Indirect DNA damage occurs when a UV-photon is absorbed in the human skin by a chromophore that does not have the ability to convert the energy into harmless heat very quickly. Molecules that do not have this ability have a long lived excited state. This long lifetime leads to a high probability...

 (free radicals and reactive oxygen species). It penetrates deeply, but it does not cause sunburn
Sunburn
A sunburn is a burn to living tissue, such as skin, which is produced by overexposure to ultraviolet radiation, commonly from the sun's rays. Usual mild symptoms in humans and other animals include red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV...

.
UVA does not damage DNA directly
Direct DNA damage
Direct DNA damage can occur when DNA directly absorbs the UV-B-photon. UVB light causes thymine base pairs next to each other in genetic sequences to bond together into thymine dimers, a disruption in the strand, which reproductive enzymes cannot copy...

 like UVB and UVC, but it can generate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which in turn can damage DNA. Because it does not cause reddening of the skin (erythema), it cannot be measured in SPF testing. There is no good clinical measurement for blockage of UVA radiation, but it is important for sunscreen
Sunscreen
Sunblock is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet radiation on the skin exposed to sunlight and thus helps protect against sunburn...

 to block both UVA and UVB. Some scientists blame the absence of UVA filters in sunscreen
Sunscreen
Sunblock is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet radiation on the skin exposed to sunlight and thus helps protect against sunburn...

s for the higher melanoma risk found for sunscreen users.

UVB light can cause direct DNA damage. The radiation excites
Excited state
Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state....

 DNA molecules in skin cells, causing aberrant covalent bond
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....

s to form between adjacent cytosine
Cytosine
Cytosine is one of the four main bases found in DNA and RNA, along with adenine, guanine, and thymine . It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached . The nucleoside of cytosine is cytidine...

 bases, producing a dimer. When DNA polymerase comes along to replicate this strand of DNA, it reads the dimer as "AA" and not the original "CC". This causes the DNA replication mechanism to add a "TT" on the growing strand. This mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

 can result in cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

ous growths, and is known as a "classical C-T mutation". The mutations caused by the direct DNA damage carry a UV signature mutation that is commonly seen in skin cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

s. The mutagen
Mutagen
In genetics, a mutagen is a physical or chemical agent that changes the genetic material, usually DNA, of an organism and thus increases the frequency of mutations above the natural background level. As many mutations cause cancer, mutagens are therefore also likely to be carcinogens...

icity of UV radiation can be easily observed in bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

l cultures. This cancer connection is one reason for concern about ozone depletion
Ozone depletion
Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere , and a much larger springtime decrease in stratospheric ozone over Earth's polar regions. The latter phenomenon...

 and the ozone hole. UVB causes some damage to collagen, but at a very much slower rate than UVA.

As a defense against UV radiation, the amount of the brown pigment melanin
Melanin
Melanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...

 in the skin increases when exposed to moderate (depending on skin type
Human skin color
Human skin color is primarily due to the presence of melanin in the skin. Skin color ranges from almost black to white with a pinkish tinge due to blood vessels underneath. Variation in natural skin color is mainly due to genetics, although the evolutionary causes are not completely certain...

) levels of radiation; this is commonly known as a sun tan. The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless heat, blocking the UV from damaging skin tissue. UVA gives a quick tan that lasts for days by oxidizing melanin that was already present, and triggers the release of the melanin
Melanin
Melanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...

 from melanocytes. UVB yields a tan that takes roughly 2 days to develop because it stimulates the body to produce more melanin. The photochemical properties of melanin make it an excellent photoprotectant
Photoprotection
Photoprotection is a group of mechanisms that nature has developed to minimize the damage that the human body suffers when exposed to UV radiation...

. Older and more widespread sunscreen chemicals cannot dissipate the energy of the excited state as efficiently as melanin, and, therefore, the penetration of these sunscreen ingredients into the lower layers of the skin may increase the amount of free radicals and reactive oxygen species (ROS
Reactive oxygen species
Reactive oxygen species are chemically reactive molecules containing oxygen. Examples include oxygen ions and peroxides. Reactive oxygen species are highly reactive due to the presence of unpaired valence shell electrons....

). In recent years, improved filtering substances have come into use in commercial sunscreen lotions that do not significantly degrade or lose their capacity to protect the skin as the exposure time increases (photostable substances).

Sunscreen
Sunscreen
Sunblock is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet radiation on the skin exposed to sunlight and thus helps protect against sunburn...

 prevents the direct DNA damage
Direct DNA damage
Direct DNA damage can occur when DNA directly absorbs the UV-B-photon. UVB light causes thymine base pairs next to each other in genetic sequences to bond together into thymine dimers, a disruption in the strand, which reproductive enzymes cannot copy...

 that causes sunburn by blockage of UVB. As such, most of these products contain an SPF rating that indicates how well they block UVB as a measure of their effectiveness. This rating, however, offers no data about protection against UVA, exposure to which does not lead to sunburn but is still harmful. In the US, the Food and Drug Administration is considering adding a star rating system to show UVA protection. A similar system is already used in some European countries. Some sunscreen lotions now include compounds such as titanium dioxide
Titanium dioxide
Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...

, which helps protect against UVA rays. Other UVA blocking compounds found in sunscreen include zinc oxide
Zinc oxide
Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...

 and avobenzone
Avobenzone
Avobenzone is an oil soluble ingredient used in sunscreen products to absorb the full spectrum of UVA rays....

.
Sunscreen safety debate

Medical organizations recommend patients protect themselves from UV radiation by using sunscreen. Five sunscreen ingredients have been shown to protect mice against skin tumors (see sunscreen
Sunscreen
Sunblock is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet radiation on the skin exposed to sunlight and thus helps protect against sunburn...

).

However, some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells. The amount of sunscreen that penetrates through the stratum corneum
Stratum corneum
The stratum corneum is the outermost layer of the epidermis, consisting of dead cells that lack nuclei and organelles. The purpose of the stratum corneum is to form a barrier to protect underlying tissue from infection, dehydration, chemicals and mechanical stress...

 may or may not be large enough to cause damage. In one study of sunscreens, the authors write:

The question whether UV filters acts on or in the skin has so far not been fully answered. Despite the fact that an answer would be a key to improve formulations of sun protection products, many publications carefully avoid addressing this question.


In an experiment by Hanson et al. published in 2006, the amount of harmful reactive oxygen species
Reactive oxygen species
Reactive oxygen species are chemically reactive molecules containing oxygen. Examples include oxygen ions and peroxides. Reactive oxygen species are highly reactive due to the presence of unpaired valence shell electrons....

 (ROS) was measured in untreated and in sunscreen treated skin. In the first 20 minutes, the film of sunscreen had a protective effect and the amount of ROS was smaller. After 60 minutes, however, the amount of absorbed sunscreen was so high, the amount of ROS was higher in the sunscreen treated skin than in the untreated skin.

Such effects can be avoided by using newer generations of filter substances or combinations that maintain their UV protective properties even after several hours of solar exposure. Sunscreen products containing photostable filters like drometrizole trisiloxane
Drometrizole trisiloxane
Drometrizole trisiloxane is a lipophilic benzotriazole derivative marketed as Mexoryl XL by L'Oréal and is used in sunscreens to absorb UV radiation. It is a broad-spectrum UV absorber with two absorption peaks, one at 303 nm and one at 344 nm . Just like Mexoryl SX , it is used exclusively in...

, bisoctrizole
Bisoctrizole
Bisoctrizole is a benzotriazole-based organic compound that is added to sunscreens to absorb UV rays....

, or bemotrizinol
Bemotrizinol
Bemotrizinol is an oil-soluble organic compound that is added to sunscreens to absorb UV rays. It is marketed as Tinosorb S by BASF and as Escalol S by International Specialty Products. A recent development is Tinosorb S Aqua, which is bemotrizinol in a PMMA matrix dispersed in water...

 have been available for many years throughout the world, but are not yet available in the U.S., whereas another high-quality filter, ecamsule
Ecamsule
Ecamsule is an organic compound which is added to many sunscreens to filter out UVA rays...

, has also been available in the U.S. since 2006.
Aggravation of skin diseases

Ultraviolet radiation causes aggravation of several skin conditions and diseases, including:
  • Systemic lupus erythematosus
    Systemic lupus erythematosus
    Systemic lupus erythematosus , often abbreviated to SLE or lupus, is a systemic autoimmune disease that can affect any part of the body. As occurs in other autoimmune diseases, the immune system attacks the body's cells and tissue, resulting in inflammation and tissue damage...

  • Sjögren’s syndrome
  • Sinear Usher syndrome
  • Rosacea
    Rosacea
    Rosacea is a chronic condition characterized by facial erythema . Pimples are sometimes included as part of the definition. Unless it affects the eyes, it is typically a harmless cosmetic condition...

  • Dermatomyositis
    Dermatomyositis
    Dermatomyositis is a connective-tissue disease related to polymyositis and Bramaticosis that is characterized by inflammation of the muscles and the skin.- Causes :...

  • Darier’s disease
  • Kindler-Weary syndrome

Eye


High intensities of UVB light are hazardous to the eyes, and exposure can cause welder's flash (photokeratitis
Photokeratitis
Photokeratitis or ultraviolet keratitis is a painful eye condition caused by exposure of insufficiently protected eyes to the ultraviolet rays from either natural or artificial sources. Photokeratitis is akin to a sunburn of the cornea and conjunctiva, and is not usually noticed until several...

 or arc eye) and may lead to cataract
Cataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...

s, pterygium
Pterygium
Pterygium most often refers to a benign growth of the conjunctiva. A pterygium commonly grows from the nasal side of the sclera. It is usually present in the palpebral fissure. It is associated with, and thought to be caused by ultraviolet-light exposure , low humidity, and dust...

, and pinguecula
Pinguecula
A pinguecula is a common type of conjunctival degeneration in the eye.-Presentation:It is seen as a yellow- white deposit on the conjunctiva adjacent to the limbus . It is to be distinguished clinically from pterygium, which is a wedge shaped area of fibrosis that appears to grow into the cornea....

 formation.

UV light is absorbed by molecules known as chromophore
Chromophore
A chromophore is the part of a molecule responsible for its color. The color arises when a molecule absorbs certain wavelengths of visible light and transmits or reflects others. The chromophore is a region in the molecule where the energy difference between two different molecular orbitals falls...

s, which are present in the eye cells and tissues. Chromophores absorb light energy from the various wavelengths at different rates - a pattern known as absorption spectrum. If too much UV light is absorbed, eye structures such as the cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...

, the lens
Lens (anatomy)
The crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a...

 and the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

 can be damaged.

Protective eyewear is beneficial to those who are working with or those who might be exposed to ultraviolet radiation, particularly short wave UV. Given that light may reach the eye from the sides, full coverage eye protection is usually warranted if there is an increased risk of exposure, as in high altitude mountaineering. Mountaineers are exposed to higher than ordinary levels of UV radiation, both because there is less atmospheric filtering and because of reflection from snow and ice.

Ordinary, untreated eyeglasses give some protection. Most plastic lenses give more protection than glass lenses, because, as noted above, glass is transparent to UVA and the common acrylic plastic used for lenses is less so. Some plastic lens materials, such as polycarbonate
Polycarbonate
PolycarbonatePhysical PropertiesDensity 1.20–1.22 g/cm3Abbe number 34.0Refractive index 1.584–1.586FlammabilityV0-V2Limiting oxygen index25–27%Water absorption – Equilibrium0.16–0.35%Water absorption – over 24 hours0.1%...

, inherently block most UV. There are protective treatments available for eyeglass lenses that need it, which will give better protection. But even a treatment that completely blocks UV will not protect the eye from light that arrives around the lens.

Degradation of polymers, pigments and dyes



Many polymers used in consumer products are degraded by UV light, and need addition of UV absorbers to inhibit attack, especially if the products are exposed to sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

. The problem appears as discoloration or fading, cracking, and, sometimes, total product disintegration if cracking has proceeded sufficiently. The rate of attack increases with exposure time and sunlight intensity.

It is known as UV degradation
UV degradation
Many natural and synthetic polymers are attacked by ultra-violet radiation and products made using these materials may crack or disintegrate . The problem is known as UV degradation, and is a common problem in products exposed to sunlight...

, and is one form of polymer degradation
Polymer degradation
Polymer degradation is a change in the properties—tensile strength, colour, shape, etc.—of a polymer or polymer-based product under the influence of one or more environmental factors such as heat, light or chemicals such as acids, alkalis and some salts...

. Sensitive polymers include thermoplastics, such as polypropylene
Polypropylene
Polypropylene , also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes...

, polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...

, and poly(methyl methacrylate) as well as speciality fibers like aramid
Aramid
Aramid fibers are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic rated body armor fabric and ballistic composites, in bicycle tires, and as an asbestos substitute. The name is a portmanteau of "aromatic polyamide"...

s. UV absorption leads to chain degradation and loss of strength at sensitive points in the chain structure. They include tertiary carbon atoms, which in polypropylene
Polypropylene
Polypropylene , also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes...

 occur in every repeat unit
Repeat unit
An essential concept which defines polymer structure, the repeat unit or repeating unit is a part of a polymer chain whose repetition would produce the complete polymer by linking the repeat units together successively along the chain, like the beads of a necklace.A repeat unit is sometimes called...

. Aramid rope must be shielded with a sheath of thermoplastic if it is to retain its strength. The impact of UV on polymers is used in nanotechnology
Nanotechnology
Nanotechnology is the study of manipulating matter on an atomic and molecular scale. Generally, nanotechnology deals with developing materials, devices, or other structures possessing at least one dimension sized from 1 to 100 nanometres...

, transplantology, X-ray lithography
X-ray lithography
300px|thumbX-ray lithography, is a process used in electronic industry to selectively remove parts of a thin film. It uses X-rays to transfer a geometric pattern from a mask to a light-sensitive chemical photoresist, or simply "resist," on the substrate...

 and other fields for modification of properties (roughness, hydrophobicity) of polymer surfaces. For example, a poly(methyl methacrylate) surface can be smoothed by vacuum ultraviolet (VUV).

In addition, many pigments and dyes absorb UV and change colour, so paintings and textiles may need extra protection both from sunlight and fluorescent bulbs, two common sources of UV radiation. Old and antique paintings such as watercolour paintings, for example, usually must be placed away from direct sunlight. Common window glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

 provides some protection by absorbing some of the harmful UV, but valuable artifacts need extra shielding. Many museums place black curtains over watercolour paintings and ancient textiles, for example. Since watercolours can have very low pigment levels, they need extra protection from UV light. Tinted glasses, such as sunglasses also provide protection from UV rays.

Blockers and absorbers


Ultraviolet Light Absorbers (UVAs) are molecules used in organic materials (polymers, paints, etc.) to absorb UV light to reduce the UV degradation
UV degradation
Many natural and synthetic polymers are attacked by ultra-violet radiation and products made using these materials may crack or disintegrate . The problem is known as UV degradation, and is a common problem in products exposed to sunlight...

 (photo-oxidation) of a material. A number of different UVAs with different absorption properties exist. UVAs can disappear over time, so monitoring of UVA levels in weathered materials is necessary.

In sunscreen
Sunscreen
Sunblock is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet radiation on the skin exposed to sunlight and thus helps protect against sunburn...

, ingredients that absorb UVA/UVB rays, such as avobenzone and octyl methoxycinnamate, are known as absorbers. They are contrasted with physical "blockers" of UV radiation such as titanium dioxide
Titanium dioxide
Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...

 and zinc oxide
Zinc oxide
Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...

. (See sunscreen
Sunscreen
Sunblock is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet radiation on the skin exposed to sunlight and thus helps protect against sunburn...

 for a more complete list.)

Applications of UV


By wavelength:
  • 13.5 nm: Extreme Ultraviolet Lithography
  • 230-400 nm: Optical sensor
    Sensor
    A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...

    s, various instrumentation
  • 230-365 nm: UV-ID, label tracking, barcode
    Barcode
    A barcode is an optical machine-readable representation of data, which shows data about the object to which it attaches. Originally barcodes represented data by varying the widths and spacings of parallel lines, and may be referred to as linear or 1 dimensional . Later they evolved into rectangles,...

    s
  • 240-280 nm: Disinfection
    Disinfection
    Disinfectants are substances that are applied to non-living objects to destroy microorganisms that are living on the objects. Disinfection does not necessarily kill all microorganisms, especially nonresistant bacterial spores; it is less effective than sterilisation, which is an extreme physical...

    , decontamination of surfaces and water (DNA
    DNA
    Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

     absorption has a peak at 260 nm)
  • 250-300 nm: Forensic analysis, drug detection
  • 270-300 nm: Protein
    Protein
    Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

     analysis, DNA sequencing
    DNA sequencing
    DNA sequencing includes several methods and technologies that are used for determining the order of the nucleotide bases—adenine, guanine, cytosine, and thymine—in a molecule of DNA....

    , drug discovery
    Drug discovery
    In the fields of medicine, biotechnology and pharmacology, drug discovery is the process by which drugs are discovered or designed.In the past most drugs have been discovered either by identifying the active ingredient from traditional remedies or by serendipitous discovery...

  • 280-400 nm: Medical imaging
    Medical imaging
    Medical imaging is the technique and process used to create images of the human body for clinical purposes or medical science...

     of cells
    Cell (biology)
    The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

  • 300-400 nm: Solid-state lighting
    Solid-state lighting
    Solid-state lighting refers to a type of lighting that uses semiconductor light-emitting diodes , organic light-emitting diodes , or polymer light-emitting diodes as sources of illumination rather than electrical filaments, plasma , or gas.The term "solid state" refers commonly to light emitted...

  • 300-365 nm: Curing
    Curing (chemistry)
    Curing is a term in polymer chemistry and process engineering that refers to the toughening or hardening of a polymer material by cross-linking of polymer chains, brought about by chemical additives, ultraviolet radiation, electron beam or heat...

     of polymer
    Polymer
    A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

    s and printer inks
  • 300-320 nm: Light therapy
    Light therapy
    Light therapy or phototherapy consists of exposure to daylight or to specific wavelengths of light using lasers, light-emitting diodes, fluorescent lamps, dichroic lamps or very bright, full-spectrum light, usually controlled with various devices...

     in medicine
  • 350-370 nm: Bug zapper
    Bug zapper
    A bug zapper, or more formally an electrical discharge insect control system is a device that attracts and kills flying insects that are attracted by light. A light source attracts insects to an electrical grid, where they are electrocuted by touching two wires with a high voltage between them...

    s (flies are most attracted to light at 365 nm)

Security



To help prevent counterfeiters, sensitive documents (e.g., credit card
Credit card
A credit card is a small plastic card issued to users as a system of payment. It allows its holder to buy goods and services based on the holder's promise to pay for these goods and services...

s, driver's license
Driver's license
A driver's license/licence , or driving licence is an official document which states that a person may operate a motorized vehicle, such as a motorcycle, car, truck or a bus, on a public roadway. Most U.S...

s, passport
Passport
A passport is a document, issued by a national government, which certifies, for the purpose of international travel, the identity and nationality of its holder. The elements of identity are name, date of birth, sex, and place of birth....

s) may also include a UV watermark
Watermark
A watermark is a recognizable image or pattern in paper that appears as various shades of lightness/darkness when viewed by transmitted light , caused by thickness or density variations in the paper...

 that is visible only under a UV-emitting light. Passports issued by most countries usually contain UV sensitive inks and security threads. Visa
Visa (document)
A visa is a document showing that a person is authorized to enter the territory for which it was issued, subject to permission of an immigration official at the time of actual entry. The authorization may be a document, but more commonly it is a stamp endorsed in the applicant's passport...

 stamps and stickers on passports of visitors contain large detailed seals invisible under normal light, but strongly visible under UV illumination. Passports issued by many nations have UV sensitive watermarks on all pages. Currencies of various countries' banknotes have an image, as well as many multicolored fibers, that are visible only under ultraviolet light.

Some brands of pepper spray
Pepper spray
Pepper spray, also known as OC spray , OC gas, and capsicum spray, is a lachrymatory agent that is used in riot control, crowd control and personal self-defense, including defense against dogs and bears...

 will leave an invisible chemical (UV dye) that is not easily washed off on a pepper sprayed attacker, which would help police identify them later.

Forensics


UV is an investigative tool at the crime scene helpful in locating and identifying bodily fluids (semen, blood, bile etc.). E.g.,
ejaculated fluids or saliva are detected by high-power UV, irrespective of the structure or colour of the surface the fluid is deposited upon.

Fluorescent lamps


Fluorescent lamp
Fluorescent lamp
A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. A fluorescent lamp converts electrical power into useful...

s produce UV radiation by ionising low-pressure mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 vapour. A phosphorescent coating on the inside of the tubes absorbs the UV and converts it to visible light.

The main mercury emission wavelength is in the UVC range. Unshielded exposure of the skin or eyes to mercury arc lamps that do not have a conversion phosphor is quite dangerous.

The light from a mercury lamp is predominantly at discrete wavelengths. Other practical UV sources with more continuous emission spectra include xenon arc lamps (commonly used as sunlight simulators), deuterium arc lamp
Deuterium arc lamp
A deuterium arc lamp is a low-pressure gas-discharge light source often used in spectroscopy when a continuous spectrum in the ultraviolet region is needed.-Principle of operation:...

s, mercury-xenon arc lamps, metal-halide arc lamps, and tungsten-halogen incandescent lamps.

Astronomy


In astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

, very hot objects preferentially emit UV radiation (see Wien's law
Wien's law
Wien's law or Wien law may refer to:* Wien approximation, an equation used to describe the short-wavelength spectrum of thermal radiation....

). Because the ozone layer blocks many UV frequencies from reaching telescopes on the surface of the Earth, most UV observations are made from space. (See UV astronomy
UV astronomy
Ultraviolet astronomy is generally used to refer to observations of electromagnetic radiation at ultraviolet wavelengths between approximately 10 and 320 nanometres; shorter wavelengths—higher energy photons—are studied by X-ray astronomy and gamma ray astronomy...

, space observatory
Space observatory
A space observatory is any instrument in outer space which is used for observation of distant planets, galaxies, and other outer space objects...

.)

Biological surveys and pest control


Some animals, including birds, reptiles, and insects such as bees, can see near-ultraviolet light. Many fruits, flowers, and seeds stand out more strongly from the background in ultraviolet wavelengths as compared to human color vision. Scorpions glow or take on a yellow to green color under UV illumination, thus assisting in the control of these arachnids. Many birds have patterns in their plumage that are invisible at usual wavelengths but observable in ultraviolet, and the urine and other secretions of some animals, including dogs, cats, and human beings, is much easier to spot with ultraviolet. Urine trails of rodents can be detected by pest control technicians for proper treatment of infested dwellings.

Butterflies use ultraviolet as a communication system for sex recognition and mating behavior.
Many insects use the ultraviolet wavelength emissions from celestial objects as references for flight navigation. A local ultraviolet emissor will normally disrupt the navigation process and will eventually attract the flying insect.

Ultraviolet traps called bug zapper
Bug zapper
A bug zapper, or more formally an electrical discharge insect control system is a device that attracts and kills flying insects that are attracted by light. A light source attracts insects to an electrical grid, where they are electrocuted by touching two wires with a high voltage between them...

s are used to eliminate various small flying insects. They are attracted to the UV light, and are killed using an electric shock, or trapped once they come into contact with the device. Different designs of ultraviolet light traps are also used by entomologists for collect
Collect
In Christian liturgy, a collect is both a liturgical action and a short, general prayer. In the Middle Ages, the prayer was referred to in Latin as collectio, but in the more ancient sources, as oratio. In English, and in this usage, "collect" is pronounced with the stress on the first syllable...

ing nocturnal insects during faunistic survey studies.

Spectrophotometry


UV/VIS spectroscopy is widely used as a technique in chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

, to analyze chemical structure
Chemical structure
A chemical structure includes molecular geometry, electronic structure and crystal structure of molecules. Molecular geometry refers to the spatial arrangement of atoms in a molecule and the chemical bonds that hold the atoms together. Molecular geometry can range from the very simple, such as...

, the most notable one being conjugated system
Conjugated system
In chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in compounds with alternating single and multiple bonds, which in general may lower the overall energy of the molecule and increase stability. Lone pairs, radicals or carbenium ions may be part of the...

s. UV radiation is often used in visible spectrophotometry
Spectrophotometry
In chemistry, spectrophotometry is the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength...

 to determine the fluorescence of a given sample. In biological research, UV light is used for quantification of nucleic acids
Quantification of nucleic acids
In molecular biology, quantitation of nucleic acids is commonly performed to determine the average concentrations of DNA or RNA present in a mixture, as well as their purity. Reactions that use nucleic acids often require particular amounts and purity for optimum performance...

 or protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s.

Sanitary compliance


UV lamps including newer LEDs (light-emitting diode) aid in the detection of organic mineral deposits that remain on surfaces where periodic cleaning and sanitizing may not be properly accomplished. Both urine and phosphate soaps are easily detected using UV inspection. Pet urine deposits in carpeting or other hard surfaces can be detected for accurate treatment and removal of mineral tracers and the odor-causing bacteria that feed on proteins within. Many hospitality industries use UV lamps to inspect for unsanitary bedding to determine lifecycle for mattress restoration as well as general performance of the cleaning staff. A perennial news feature for many television news organizations involves an investigative reporter's using a similar device to reveal unsanitary conditions in hotels, public toilets, hand rails, and such.

Air purification


Using a catalytic reaction from titanium dioxide and UV light exposure, a strong oxidative effect occurs on any organic objects that pass through the media, converting otherwise irritating pathogens, pollens, and mold spores into harmless inert byproducts.
The cleansing mechanism of UV is a photochemical process. The contaminants that pollute the indoor environment are almost entirely based upon organic or carbon-based compounds. These compounds break down when exposed to high-intensity UV at 240 to 280 nm. Short-wave ultraviolet light can destroy DNA in living microorganisms and break down organic material found in indoor air. UVC's effectiveness is directly related to intensity and exposure time.

UV light has also been shown (by KJ Scott et al) as effective in reducing gaseous contaminants such as carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 and VOCs
Volatile organic compound
Volatile organic compounds are organic chemicals that have a high vapor pressure at ordinary, room-temperature conditions. Their high vapor pressure results from a low boiling point, which causes large numbers of molecules to evaporate or sublimate from the liquid or solid form of the compound and...

. Scott and his colleagues demonstrated that the correct mixture of UV lamps radiating at 184 and 254 nm can remove low concentrations of hydrocarbons and carbon monoxide, if the lamps are held in a radiation chamber (a box or drum) and the air is recycled between the room and the reaction chamber. This arrangement prevents the introduction of ozone into the treated air. Alternatively, air may be treated by passing by a single UV source operating at 184 nm and subsequent catalysis with iron pentaoxide. The iron oxides remove the ozone produced by the UV lamp.

Analyzing minerals


Ultraviolet lamps are also used in analyzing minerals and gems
Gemstone
A gemstone or gem is a piece of mineral, which, in cut and polished form, is used to make jewelry or other adornments...

, and in other detective work including authentication of various collectible
Collectible
A collectable or collectible is any object regarded as being of value or interest to a collector . There are numerous types of collectables and terms to denote those types. An antique is a collectable that is old...

s. Materials may look the same under visible light, but fluoresce
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...

 to different degrees under ultraviolet light, or may fluoresce differently under short wave ultraviolet versus long wave ultraviolet.

Authentication


In other detective work including authentication of various collectibles and art, and detecting counterfeit currency absent of marker dyes. Materials may look the same under visible light, but fluoresce to different degrees under ultraviolet light, or may fluoresce differently under short-wave ultraviolet versus long-wave ultraviolet.

Chemical markers


UV fluorescent dye
Dye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....

s are used in many applications (for example, biochemistry
Biochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...

 and forensics). The Green Fluorescent Protein
Green fluorescent protein
The green fluorescent protein is a protein composed of 238 amino acid residues that exhibits bright green fluorescence when exposed to blue light. Although many other marine organisms have similar green fluorescent proteins, GFP traditionally refers to the protein first isolated from the...

 (GFP) is often used in genetics
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

 as a marker. Many substances, such as proteins, have significant light absorption bands in the ultraviolet that are of use and interest in biochemistry and related fields. UV-capable spectrophotometers are common in such laboratories.

Photochemotherapy


Exposure to UVA light while the skin is hyper-photosensitive by taking psoralen
Psoralen
Psoralen is the parent compound in a family of natural products known as furocoumarins. It is structurally related to coumarin by the addition of a fused furan ring, and may be considered as a derivative of umbelliferone...

s is an effective treatment for psoriasis
Psoriasis
Psoriasis is an autoimmune disease that appears on the skin. It occurs when the immune system mistakes the skin cells as a pathogen, and sends out faulty signals that speed up the growth cycle of skin cells. Psoriasis is not contagious. However, psoriasis has been linked to an increased risk of...

 called PUVA
PUVA
PUVA is a psoralen + UVA treatment for eczema, psoriasis, graft-versus-host disease and vitiligo, and mycosis fungoides. The psoralen is applied or taken orally to sensitize the skin, then the skin is exposed to UVA. Long term use has been associated with higher rates of skin cancer.Psoralens are...

. Due to the potential of psoralens to cause damage to the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

, PUVA
PUVA
PUVA is a psoralen + UVA treatment for eczema, psoriasis, graft-versus-host disease and vitiligo, and mycosis fungoides. The psoralen is applied or taken orally to sensitize the skin, then the skin is exposed to UVA. Long term use has been associated with higher rates of skin cancer.Psoralens are...

 may be used only a limited number of times over a patient's lifetime.

Phototherapy


Exposure to UVB light, in particular, the 310 nm narrowband UVB range, is an effective long-term treatment for many skin conditions like psoriasis
Psoriasis
Psoriasis is an autoimmune disease that appears on the skin. It occurs when the immune system mistakes the skin cells as a pathogen, and sends out faulty signals that speed up the growth cycle of skin cells. Psoriasis is not contagious. However, psoriasis has been linked to an increased risk of...

, vitiligo
Vitiligo
Vitiligo is a condition that causes depigmentation of sections of skin. It occurs when melanocytes, the cells responsible for skin pigmentation, die or are unable to function. The cause of vitiligo is unknown, but research suggests that it may arise from autoimmune, genetic, oxidative stress,...

, eczema
Eczema
Eczema is a form of dermatitis, or inflammation of the epidermis . In England, an estimated 5.7 million or about one in every nine people have been diagnosed with the disease by a clinician at some point in their lives.The term eczema is broadly applied to a range of persistent skin conditions...

, and others. UVB phototherapy does not require additional medications or topical preparations for the therapeutic benefit; only the light exposure is needed. However, phototherapy can be effective when used in conjunction with certain topical treatments such as anthralin, coal tar, and Vitamin A and D derivatives, or systemic treatments such as methotrexate and soriatane.

Typical treatment regimes involve short exposure to UVB rays 3 to 5 times a week at a hospital or clinic, and repeated sessions may be required before results are noticeable. Almost all of the conditions that respond to UVB light are chronic problems, so continuous treatment is required to keep those problems in check. Home UVB systems are common solutions for those whose conditions respond to treatment. Home systems permit patients to treat themselves every other day (the ideal treatment regimen for most) without the frequent, costly trips to the office/clinic and back.

Side-effects may include itching and redness of the skin due to UVB exposure, and possibly sunburn, if patients do not minimize exposure to natural UV rays during treatment days. Cataracts can frequently develop if the eyes are not protected from UVB light exposure. There is no link between an increase in the patient's risk for skin cancer and the proper use of UVB phototherapy. "Proper use" is generally defined as reaching the "Sub-Erythemic Dose" (S.E.D.), the maximum amount of UVB your skin can receive without burning.

Certain fungal growths under the toenail can be treated using a specific wavelength of UV delivered from a high-power LED (light-emitting diode) and can be safer than traditional systemic drugs.

Photolithography


Ultraviolet radiation is used for very fine resolution photolithography
Photolithography
Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate...

, a procedure wherein a chemical called a photoresist is exposed to UV radiation that has passed through a mask. The light causes chemical reactions to occur in the photoresist, and, after development (a step that removes either the exposed or the unexposed photoresist), a pattern determined by the mask remains on the sample. Steps may then be taken to "etch" away areas of the sample where no photoresist remains.

UV radiation is used extensively in the electronics industry because photolithography is used in the manufacture of semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

s, integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

 components, and printed circuit board
Printed circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...

s.

Checking electrical insulation


An application of UV is to detect corona discharge
Corona discharge
In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor that is electrically energized...

 (often called "corona") on electrical apparatus. Degradation of insulation in electrical apparatus or pollution causes corona, wherein a strong electric field ionizes the air and excites nitrogen molecules, causing the emission of ultraviolet radiation. The corona degrades the insulation level of the apparatus. Corona produces ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...

 and to a lesser extent nitrogen oxide
Nitrogen oxide
Nitrogen oxide can refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds:* Nitric oxide, also known as nitrogen monoxide, , nitrogen oxide* Nitrogen dioxide , nitrogen oxide...

, which may subsequently react with water in the air to form nitrous acid
Nitrous acid
Nitrous acid is a weak and monobasic acid known only in solution and in the form of nitrite salts.Nitrous acid is used to make diazides from amines; this occurs by nucleophilic attack of the amine onto the nitrite, reprotonation by the surrounding solvent, and double-elimination of water...

 and nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...

 vapour in the surrounding air.

Sterilization


Ultraviolet lamps are used to sterilize
Sterilization (microbiology)
Sterilization is a term referring to any process that eliminates or kills all forms of microbial life, including transmissible agents present on a surface, contained in a fluid, in medication, or in a compound such as biological culture media...

 workspaces and tools used in biology laboratories and medical facilities. Commercially available low-pressure mercury-vapor lamps emit about 86% of their light at 254 nanometers (nm), which coincides very well with one of the two peaks of the germicidal effectiveness curve (i.e., effectiveness for UV absorption by DNA). One of these peaks is at about 265 nm and the other is at about 185 nm. Although 185 nm is better absorbed by DNA, the quartz glass used in commercially available lamps, as well as environmental media such as water, are more opaque to 185 nm than 254 nm (C. von Sonntag et al., 1992). UV light at these germicidal wavelengths causes adjacent thymine
Thymine
Thymine is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine is also known as 5-methyluracil, a pyrimidine nucleobase. As the name suggests, thymine may be derived by methylation of uracil at...

 molecules on DNA to dimerize; if enough of these defects accumulate on a microorganism's DNA, its replication is inhibited, thereby rendering it harmless (even though the organism may not be killed outright). However, since microorganisms can be shielded from ultraviolet light in small cracks and other shaded areas, these lamps are used only as a supplement to other sterilization techniques.

Disinfecting drinking water


UV radiation can be an effective viricide and bactericide. Disinfection using UV radiation is commonly used in wastewater treatment applications and is finding an increased usage in drinking water treatment. Many bottlers of spring water use UV disinfection equipment to sterilize their water. Solar water disinfection
Solar water disinfection
Solar water disinfection, also known as SODIS is a method of disinfecting water using only sunlight and plastic PET bottles. SODIS is a free and effective method for decentralized water treatment, usually applied at the household level and is recommended by the World Health Organization as a viable...

 is the process of using PET
Polyethylene terephthalate
Polyethylene terephthalate , commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination...

 bottles and sunlight to disinfect water.

New York City has approved the construction of a 2.2 billion US gallon per day (535,000 m3/hr) ultraviolet drinking water disinfection facility due to be online in 2012. There are also several facilities under construction and several in operation that treat waste water with several stages of filters, hydrogen peroxide, and UV light to bring the water up to drinking standards. One such facility exists in Orange County, California which is designed to treat wastewater and convert it into high-quality water for Indirect Potable Reuse. NASA has examined the use of this technology, using titanium dioxide as catalyst
Catalysis
Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....

, for breaking down harmful products in spacecraft waste water.

It used to be thought that UV disinfection was more effective for bacteria and viruses, which have more exposed genetic material, than for larger pathogens that have outer coatings or that form cyst states (e.g., Giardia
Giardia
Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada in the supergroup "Excavata" that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis, commonly known as Beaver fever...

) that shield their DNA from the UV light. However, it was recently discovered that ultraviolet radiation can be somewhat effective for treating the microorganism Cryptosporidium
Cryptosporidium
Cryptosporidium is a protozoan that can cause gastro-intestinal illness with diarrhea in humans.Cryptosporidium is the organism most commonly isolated in HIV positive patients presenting with diarrhea...

. The findings resulted in the use of UV radiation as a viable method to treat drinking
water. Giardia in turn has been shown to be very susceptible to UV-C when the tests were based on infectivity rather than excystation. It has been found that protists are able to survive high UV-C doses but are sterilized at low doses.

Solar water disinfection
Solar water disinfection
Solar water disinfection, also known as SODIS is a method of disinfecting water using only sunlight and plastic PET bottles. SODIS is a free and effective method for decentralized water treatment, usually applied at the household level and is recommended by the World Health Organization as a viable...

 (SODIS) has been extensively researched in Switzerland and has proven ideal to treat small quantities of water cheaply using natural sunlight. Contaminated water is poured into transparent plastic bottles and exposed to full sunlight for six hours. The sunlight treats the contaminated water through two synergetic mechanisms: UV-A irradiation and increased water temperature. If the water temperatures rises above 50 °C, the disinfection process is three times faster.

Food processing


As consumer demand for fresh and "fresh-like" food products increases, the demand for nonthermal methods of food processing
Food processing
Food processing is the set of methods and techniques used to transform raw ingredients into food or to transform food into other forms for consumption by humans or animals either in the home or by the food processing industry...

 is likewise on the rise. In addition, public awareness regarding the dangers of food poisoning is also raising demand for improved food processing methods. Ultraviolet radiation is used in several food processes to kill unwanted microorganisms. UV light can be used to pasteurize
Pasteurization
Pasteurization is a process of heating a food, usually liquid, to a specific temperature for a definite length of time, and then cooling it immediately. This process slows microbial growth in food...

 fruit juices by flowing the juice over a high-intensity ultraviolet light source. The effectiveness of such a process depends on the UV absorbance of the juice (see Beer's law).

Fire detection


Ultraviolet detectors generally use either a solid-state device, such as one based on silicon carbide
Silicon carbide
Silicon carbide , also known as carborundum, is a compound of silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...

 or aluminium nitride
Aluminium nitride
Aluminium nitride is a nitride of aluminium. Its wurtzite phase is a wide band gap semiconductor material, giving it potential application for deep ultraviolet optoelectronics.-History:...

, or a gas-filled tube as the sensing element. UV detectors that are sensitive to UV light in any part of the spectrum respond to irradiation by sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

 and artificial light. A burning hydrogen flame, for instance, radiates strongly in the 185- to 260-nanometer range and only very weakly in the IR
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 region, whereas a coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

 fire emits very weakly in the UV band yet very strongly at IR wavelengths; thus, a fire detector that operates using both UV and IR detectors is more reliable than one with a UV detector alone. Virtually all fires emit some radiation
Thermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....

 in the UVC band, whereas the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

's radiation at this band is absorbed by the Earth's atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

. The result is that the UV detector is "solar blind", meaning it will not cause an alarm in response to radiation from the Sun, so it can easily be used both indoors and outdoors.

UV detectors are sensitive to most fires, including hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

s, metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

s, sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

, hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

, hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...

, and ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

. Arc welding
Arc welding
Arc welding is a type of welding that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct or alternating current, and consumable or non-consumable electrodes...

, electrical arcs, lightning
Lightning
Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...

, X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

s used in nondestructive metal testing equipment (though this is highly unlikely), and radioactive materials can produce levels that will activate a UV detection system. The presence of UV-absorbing gases and vapors will attenuate the UV radiation from a fire, adversely affecting the ability of the detector to detect flames. Likewise, the presence of an oil mist in the air or an oil film on the detector window will have the same effect.

Herpetology


Reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s need long wave UV light for de novo synthesis of vitamin D. Vitamin D is needed to metabolize calcium for bone and egg production. Thus, in a typical reptile enclosure, a fluorescent UV lamp should be available for vitamin D synthesis. This should be combined with the provision of heat for basking, either in the same or by another lamp.

Curing of electronic potting resins


Electronic components that require clear transparency for light to exit or enter (photo voltaic panels and sensors) can be potted using acrylic resins that are cured using UV light energy. The advantages are low VOC emissions and rapid curing.

Curing of inks, adhesives, varnishes and coatings


Certain inks, coatings, and adhesives are formulated with photoinitiators and resins. When exposed to the correct energy and irradiance in the required band of UV light, polymerization occurs, and so the adhesives harden or cure. Usually, this reaction is very quick, a matter of a few seconds. Applications include glass and plastic bonding, optical fiber
Optical fiber
An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...

 coatings, the coating of flooring, UV Coating
UV Coating
"UV coating" refers to surface treatments which are either cured by ultraviolet radiation, or protect the underlying material from its harmful effects.-Ultra-violet coating of paper:...

 and paper finishes in offset printing
Printing
Printing is a process for reproducing text and image, typically with ink on paper using a printing press. It is often carried out as a large-scale industrial process, and is an essential part of publishing and transaction printing....

, and dental fillings. Curing of decorative finger nail "gels".

An industry has developed around the manufacture of UV sources for UV curing applications. This includes UV lamps, UV LED
LEd
LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....

s, and Excimer
Excimer
An excimer is a short-lived dimeric or heterodimeric molecule formed from two species, at least one of which is in an electronic excited state. Excimers are often diatomic and are composed of two atoms or molecules that would not bond if both were in the ground state. The lifetime of an excimer is...

 Flash lamps. Fast processes such as flexo or offset printing require high-intensity light focused via reflectors onto a moving substrate and medium; and high-pressure Hg
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 (mercury) or Fe
FE
Fe or FE may refer to:* Iron * Fe , the f-rune of the Younger Futhark* Fe * Fe * "Fe" , a song by Jorge González...

 (iron, doped)-based bulbs are used, which can be energized with electric arc or microwaves. Lower-power sources (fluorescent lamps, LED) can be used for static applications, and, in some cases, small high-pressure lamps can have light focused and transmitted to the work area via liquid-filled or fiber-optic light guides.

Sun tanning


Sun tanning
Sun tanning
Sun tanning or simply tanning is the process whereby skin color is darkened or tanned. The process is most often a result of exposure to ultraviolet radiation from the sun or from artificial sources, such as a tanning bed, but can also be a result of windburn or reflected light...

 describes a darkening of the skin in a natural physiological response stimulated by exposure to ultraviolet radiation from sunshine
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

 (or a sunbed
Sunbed
A sunbed , tanning bed or sun tanning bed is a device which emits ultraviolet radiation to produce a cosmetic tan. Regular tanning beds use several fluorescent lamps that have phosphor blends designed to emit UV in a spectrum that is somewhat similar to the sun...

). With excess exposure to the sun, a suntanned area can also develop sunburn. The increased production of melanin is triggered by the direct DNA damage
Direct DNA damage
Direct DNA damage can occur when DNA directly absorbs the UV-B-photon. UVB light causes thymine base pairs next to each other in genetic sequences to bond together into thymine dimers, a disruption in the strand, which reproductive enzymes cannot copy...

. This kind of damage is recognized by the body and as a defense against UV radiation the skin produces more melanin. Melanin dissipates the UV energy as harmless heat, and therefore it is an excellent photoprotectant
Photoprotection
Photoprotection is a group of mechanisms that nature has developed to minimize the damage that the human body suffers when exposed to UV radiation...

. Melanin protects against the direct DNA damage and against the indirect DNA damage
Indirect DNA damage
Indirect DNA damage occurs when a UV-photon is absorbed in the human skin by a chromophore that does not have the ability to convert the energy into harmless heat very quickly. Molecules that do not have this ability have a long lived excited state. This long lifetime leads to a high probability...

. Sunscreen protects only against the direct DNA damage, but increases the indirect DNA damage. Some studies suggest that this may be the cause of the higher incidence of melanoma found in sunscreen users compared to non-users.

Erasing EPROM modules


Some EPROM
EPROM
An EPROM , or erasable programmable read only memory, is a type of memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile. It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages...

 (erasable programmable read-only memory) modules are erased by exposure to UV radiation. These modules often have a transparent glass (quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

) window on the top of the chip that allows the UV radiation in. These have been largely superseded by EEPROM
EEPROM
EEPROM stands for Electrically Erasable Programmable Read-Only Memory and is a type of non-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed, e.g., calibration...

 and flash memory
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...

 chips in most devices.

Preparing low surface energy polymers


UV radiation is useful in preparing low surface energy polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

s for adhesives. Polymers exposed to UV light will oxidize, thus raising the surface energy
Surface energy
Surface energy quantifies the disruption of intermolecular bonds that occur when a surface is created. In the physics of solids, surfaces must be intrinsically less energetically favorable than the bulk of a material, otherwise there would be a driving force for surfaces to be created, removing...

 of the polymer. Once the surface energy of the polymer has been raised, the bond between the adhesive and the polymer is stronger.

Reading otherwise illegible papyruses and manuscripts


Using multi-spectral imaging it is possible to read illegible papyrus
Papyrus
Papyrus is a thick paper-like material produced from the pith of the papyrus plant, Cyperus papyrus, a wetland sedge that was once abundant in the Nile Delta of Egypt....

es, such as the burned papyruses of the Villa of the Papyri
Villa of the Papyri
The Villa of the Papyri is a private house in the ancient Roman city of Herculaneum . Situated north-west of the township, the residence sits halfway up the slope of the volcano Vesuvius without other buildings to obstruct the view. The villa suburbana was owned by Julius Caesar's father-in-law,...

 or of Oxyrhynchus
Oxyrhynchus
Oxyrhynchus is a city in Upper Egypt, located about 160 km south-southwest of Cairo, in the governorate of Al Minya. It is also an archaeological site, considered one of the most important ever discovered...

, or the Archimedes palimpsest
Archimedes Palimpsest
The Archimedes Palimpsest is a palimpsest on parchment in the form of a codex. It originally was a copy of an otherwise unknown work of the ancient mathematician, physicist, and engineer Archimedes of Syracuse and other authors, which was overwritten with a religious text.Archimedes lived in the...

. The technique involves taking pictures of the illegible papyruses using different filters in the infrared or ultraviolet range, finely tuned to capture certain wavelengths of light. Thus, the optimum spectral portion can be found for distinguishing ink from paper on the papyrus surface.
Simple NUV sources can be used to highlight faded iron-based ink
Ink
Ink is a liquid or paste that contains pigments and/or dyes and is used to color a surface to produce an image, text, or design. Ink is used for drawing and/or writing with a pen, brush, or quill...

 on vellum.

Lasers


Ultraviolet lasers have applications in industry (laser engraving
Laser engraving
Laser engraving, or laser marking, is the practice of using lasers to engrave or mark an object. The technique does not involve the use of inks, nor does it involve tool bits which contact the engraving surface and wear out...

), medicine (dermatology
Dermatology
Dermatology is the branch of medicine dealing with the skin and its diseases, a unique specialty with both medical and surgical aspects. A dermatologist takes care of diseases, in the widest sense, and some cosmetic problems of the skin, scalp, hair, and nails....

 and keratectomy), free air secure communications and computing (optical storage
Optical storage
Optical storage is a term from engineering referring to the storage of data on an optically readable medium. Data is recorded by making marks in a pattern that can be read back with the aid of light, usually a beam of laser light precisely focused on a spinning disc. An older example, that does...

). They can be made by applying frequency conversion
Frequency conversion
Frequency conversion may refer to different processes affecting frequency of physical phenomena:* A frequency changer is an electronic device that converts alternating current of one frequency to alternating current of another frequency....

 to lower-frequency lasers, or from Ce:LiSAF crystals (cerium
Cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight...

 doped
Dopant
A dopant, also called a doping agent, is a trace impurity element that is inserted into a substance in order to alter the electrical properties or the optical properties of the substance. In the case of crystalline substances, the atoms of the dopant very commonly take the place of elements that...

 with lithium strontium aluminum fluoride), a process developed in the 1990s at Lawrence Livermore National Laboratory
Lawrence Livermore National Laboratory
The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...

.

UV solar cells and UV degradation of solar cells


Japan's National Institute of Advanced Industrial Science and Technology
National Institute of Advanced Industrial Science and Technology
The , or AIST, is a Japanese research facility headquartered in Tokyo, and most of the workforce is located in Tsukuba Science City, Ibaraki, and in several cities throughout Japan. The institute is managed to integrate scientific and engineering knowledge to address socio-economic needs...

 (AIST) has succeeded in developing a transparent
Transparency and translucency
In the field of optics, transparency is the physical property of allowing light to pass through a material; translucency only allows light to pass through diffusely. The opposite property is opacity...

 solar cell that uses ultraviolet light to generate electricity but allows visible light to pass through it. Most conventional solar cells use visible and infrared light to generate electricity. In contrast, the innovative new solar cell uses ultraviolet radiation. Used to replace conventional window glass, the installation surface area could be large, leading to potential uses that take advantage of the combined functions of power generation, lighting and temperature control.

Also PEDOT
Pedot
Pedot is the eleventh album of the Finnish rock band CMX. "Pedot" means "Beasts" in Finnish.The opening track "Eteläisen tähtitaivaan kartoitus" breaks a CMX tradition of starting their albums with powerful rock songs. It is a minimalistic piano-based ballad with no drums...

-PSS
PSS
- Science :*Packet Switch Stream, a British packet-switched network*Perceived Stress Scale, a psychological instrument for measuring perceived stress in humans...

 solar cells is an ultraviolet (UV) light-selective and -sensitive photovoltaic cell easily fabricated.

On the other hand, a nanocrystalline
Nanocrystalline
A nanocrystalline material is a polycrystalline material with a crystallite size of only a few nanometers. These materials fill the gap between amorphous materials without any longe range order and crystalline materials with a clear three dimensional long range order.X-ray diffraction is commonly...

 layer of Cu2O in the construction of photovoltaic cells increases their ability to utilize UV radiations for photocurrent generation.

Nondestructive testing


UV light of a specified spectrum and intensity is used to stimulate fluorescent dyes so as to highlight defects in a broad range of materials. These dyes may be carried into surface-breaking defects by capillary action (liquid penetrant inspection) or they may be bound to ferrite particles caught in magnetic leakage fields in ferrous materials (magnetic particle inspection
Magnetic-particle inspection
Magnetic particle inspection is a non-destructive testing process for detecting surface and slightly subsurface discontinuities in ferroelectric materials such as iron, nickel, cobalt, and some of their alloys. The process puts a magnetic field into the part. The piece can be magnetized by direct...

).

Evolutionary significance


Evolution of early reproductive proteins and enzymes is attributed in modern models of evolutionary theory to ultraviolet light. UVB light causes thymine
Thymine
Thymine is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine is also known as 5-methyluracil, a pyrimidine nucleobase. As the name suggests, thymine may be derived by methylation of uracil at...

 base pairs next to each other in genetic sequences to bond together into thymine dimers, a disruption in the strand that reproductive enzymes cannot copy (see picture above). This leads to frameshifting during genetic replication and protein synthesis, usually killing the organism. As early prokaryotes began to approach the surface of the ancient oceans, before the protective ozone layer had formed, blocking out most wavelengths of UV light, they almost invariably died out. The few that survived had developed enzymes that verified the genetic material and broke up thymine dimer bonds, known as base excision repair
Base excision repair
In biochemistry and genetics, base excision repair is a cellular mechanism that repairs damaged DNA throughout the cell cycle. It is responsible primarily for removing small, non-helix-distorting base lesions from the genome. The related nucleotide excision repair pathway repairs bulky...

 enzymes. Many enzymes and proteins involved in modern mitosis
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...

 and meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....

 are similar to excision repair enzymes, and are believed to be evolved modifications of the enzymes originally used to overcome UV light.

See also

  • Black light
    Black light
    A black light, also referred to as a UV light, ultraviolet light, or Wood's lamp, is a lamp that emits ultraviolet radiation in the long-wave range, and little visible light...

  • High-energy visible light
  • Infrared light
  • Polymer degradation
    Polymer degradation
    Polymer degradation is a change in the properties—tensile strength, colour, shape, etc.—of a polymer or polymer-based product under the influence of one or more environmental factors such as heat, light or chemicals such as acids, alkalis and some salts...

  • Risks and benefits of sun exposure
    Risks and benefits of sun exposure
    The ultraviolet radiation in sunlight, though a principal source of vitamin D3 compared to diet, is mutagenic. Supplementing diet with vitamin D3 supplies vitamin D without this mutagenic effect, but bypasses natural mechanisms that would prevent overdoses of vitamin D generated internally from...

  • Sun tanning
    Sun tanning
    Sun tanning or simply tanning is the process whereby skin color is darkened or tanned. The process is most often a result of exposure to ultraviolet radiation from the sun or from artificial sources, such as a tanning bed, but can also be a result of windburn or reflected light...

  • Tanning lamp
    Tanning lamp
    Tanning lamps are the part of a tanning bed, booth or other tanning device which produces ultraviolet light responsible for tanning. While there are literally hundreds of different kinds of tanning lamps, they can usually be classified in two basic groups: low pressure and high pressure...

  • Titanium dioxide
    Titanium dioxide
    Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...

  • Ultraviolet blood irradiation
  • Ultraviolet light and cancer
    Ultraviolet light and cancer
    The article examines the connection between natural ultraviolet light radiation and the incidence of cancer in human beings.The connection between UV radiation and cancer is well known to scientists, and what is debated by public policy advocates is the role of ozone. Some researchers have claimed...

  • Ultraviolet photography
    Ultraviolet photography
    Ultraviolet photography is a photographic process of recording images by using light from the ultraviolet spectrum only.-Overview:Light which is visible to the human eye covers the spectral region from about 400 to 750 nanometers. This is the radiation spectrum used in normal photography...

  • UV degradation
    UV degradation
    Many natural and synthetic polymers are attacked by ultra-violet radiation and products made using these materials may crack or disintegrate . The problem is known as UV degradation, and is a common problem in products exposed to sunlight...

  • UV index
    UV index
    The ultraviolet index or UV Index is an international standard measurement of the strength of the ultraviolet radiation from the sun at a particular place on a particular day...

  • UV stabilizers in plastics
    UV Stabilizers in plastics
    UV light stabilizers are used frequently in plastics, including cosmetics and films. The primary function is to protect the substance from the long-term degradation effects from light, most frequently ultraviolet light...

  • UVGI
  • Weather testing of polymers
    Weather testing of polymers
    Weather testing of polymers is the controlled polymer degradation and polymer coating degradation under lab or natural conditions.Just like erosion of rocks, natural phenomena can cause degradation in polymer systems. The elements of most concern to polymers are Ultraviolet radiation, moisture and...

  • Wood's lamp

Further reading