A
Fresnel lens is a type of
lensA lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
originally developed by
FrenchThe French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
physicistPhysics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
Augustin-Jean FresnelAugustin-Jean Fresnel , was a French engineer who contributed significantly to the establishment of the theory of wave optics. Fresnel studied the behaviour of light both theoretically and experimentally....
for
lighthouseA lighthouse is a tower, building, or other type of structure designed to emit light from a system of lamps and lenses or, in older times, from a fire, and used as an aid to navigation for maritime pilots at sea or on inland waterways....
s.
The design allows the construction of lenses of large
apertureIn optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...
and short
focal lengthThe focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus...
without the mass and volume of material that would be required by a lens of conventional design. Compared to conventional bulky lenses, the Fresnel lens is much thinner, larger, and flatter, and captures more oblique light from a light source, thus allowing lighthouses to be visible over much greater distances.
History
The idea of creating a thinner, lighter lens by making it with separate sections mounted in a frame is often attributed to
Georges-Louis Leclerc, Comte de BuffonGeorges-Louis Leclerc, Comte de Buffon was a French naturalist, mathematician, cosmologist, and encyclopedic author.His works influenced the next two generations of naturalists, including Jean-Baptiste Lamarck and Georges Cuvier...
. The
marquis de CondorcetMarie Jean Antoine Nicolas de Caritat, marquis de Condorcet , known as Nicolas de Condorcet, was a French philosopher, mathematician, and early political scientist whose Condorcet method in voting tally selects the candidate who would beat each of the other candidates in a run-off election...
(1743–1794) proposed grinding such a lens from a single thin piece of glass.
French physicist and engineer
Augustin-Jean FresnelAugustin-Jean Fresnel , was a French engineer who contributed significantly to the establishment of the theory of wave optics. Fresnel studied the behaviour of light both theoretically and experimentally....
is most often given credit for the development of the multi-part lens for use in lighthouses. According to
SmithsonianSmithsonian is the official journal published by the Smithsonian Institution in Washington, D.C. The first issue was published in 1970.-History:...
magazine, the first Fresnel lens was used in 1823 in the
Cordouan lighthouseCordouan lighthouse is an active lighthouse located 7 km at sea, near the mouth of the Gironde estuary in France. At a height of it is the tenth tallest "traditional lighthouse" in the world....
at the mouth of the
Gironde estuaryThe Gironde is a navigable estuary , in southwest France and is formed from the meeting of the rivers Dordogne and Garonne just below the centre of Bordeaux...
; its light could be seen from more than 20 miles (32.2 km) out. Scottish physicist Sir
David BrewsterSir David Brewster KH PRSE FRS FSA FSSA MICE was a Scottish physicist, mathematician, astronomer, inventor, writer and university principal.-Early life:...
is credited with convincing the United Kingdom to adopt these lenses in their lighthouses.
Description
The Fresnel lens reduces the amount of material required compared to a conventional spherical lens by dividing the lens into a set of concentric annular sections known as "
Fresnel zoneIn optics and radio communications , a Fresnel zone , named for physicist Augustin-Jean Fresnel, is one of a number of concentric ellipsoids which define volumes in the radiation pattern of a circular aperture...
s". In theory there are infinitely many such zones.
In the first (and largest) variations of the lens, each zone was actually a separate prism. Though a Fresnel lens might appear like a single piece of glass, closer examination reveals that it is many small pieces. 'Single-piece' Fresnel lenses were later produced, being used for automobile headlamps, brake, parking, and turn signal lenses, and so on. In modern times, computer-controlled milling equipment (CNC) might be used to manufacture more complex lenses.
In each of these zones, the overall thickness of the lens is decreased, effectively dividing the continuous surface of a standard lens into a set of surfaces of the same curvature, with stepwise discontinuities between them. A Fresnel lens can be regarded as an array of prisms arranged in a circular fashion, with steeper prisms on the edges and a nearly flat convex center.
Fresnel lens design allows a substantial reduction in thickness (and thus mass and volume of material), at the expense of reducing the imaging quality of the lens, which is why precise imaging applications such as photography still use conventional bulky (non-Fresnel) lenses.
Fresnel lenses are usually made of glass or plastic; their size varies from large (old historical lighthouses, meter size) to medium (book-reading aids, OHP viewgraph projectors) to small (
TLRA twin-lens reflex camera is a type of camera with two objective lenses of the same focal length. One of the lenses is the photographic objective or "taking lens" , while the other is used for the viewfinder system, which is usually viewed from above at waist level...
/
SLRA single-lens reflex camera is a camera that typically uses a semi-automatic moving mirror system that permits the photographer to see exactly what will be captured by the film or digital imaging system, as opposed to pre-SLR cameras where the view through the viewfinder could be significantly...
camera screens, micro-optics). In many cases they are very thin and flat, almost flexible, with thicknesses in the 1 to 5 millimetre range.
Sizes of lighthouse lenses
Fresnel's lighthouse lenses ordinarily fell into six
orders based on their focal length. The order of a Fresnel lens is approximately the
dioptreA dioptre, or diopter, is a unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in metres . It is thus a unit of reciprocal length. For example, a 3-dioptre lens brings parallel rays of light to focus at metre...
or optical power of the lens. The dioptre (also spelled diopter) is the reciprocal of the focal length of the lens in meters. A Fresnel lens with a focal length of 50 cm or 0.5 m would be classified as a second-order lens.
However, there are a few
hyperradiant Fresnel lensHyper-radial or hyperradiant Fresnel lenses are Fresnel lenses larger than "first order" lenses. They have a focal length of 1330 mm. The idea was mentioned by Thomas Stevenson in 1869 and first proposed by John Richardson Wigham in 1872, and again proposed by Thomas Stevenson in 1885.The...
es—the largest ever made—'off the chart' of sixth through first order. One such lens was on hand when it was decided to build and outfit the
Makapuu Point LightThe Makapuu Point Light on the island of Oahu has the largest lens of any lighthouse in the United States. It was listed on the National Register of Historic Places in 1977.-History:...
. Rather than order a new lens, the huge optic construction—twelve feet tall and with over a thousand prisms—was used there.
The largest (first-order) lens has a focal length of 920 mm (36 in) and an optical area 2590 mm (8.5 ft) high. The complete assembly is about 3.7 m (12 ft) tall and 1.8 m (6 ft) wide. The smallest (sixth-order) has a focal length of 150 mm (5.9 in) and an optical area 433 mm (17 in) high.
Subsequent development extended this to seventh and eighth orders, an intermediate three-and-one-half order, and two orders even larger than first:
mesoradial and
hyperradialHyper-radial or hyperradiant Fresnel lenses are Fresnel lenses larger than "first order" lenses. They have a focal length of 1330 mm. The idea was mentioned by Thomas Stevenson in 1869 and first proposed by John Richardson Wigham in 1872, and again proposed by Thomas Stevenson in 1885.The...
.
Examples and uses
The use of a Fresnel lens for image projection reduces image quality, so they tend to be used only where quality is not critical or where the bulk of a solid lens would be prohibitive. Cheap Fresnel lenses can be stamped or molded of transparent plastic and are used in
overhead projectorAn overhead projector is a variant of slide projector that is used to display images to an audience.-Mechanism:An overhead projector typically consists of a large box containing a very bright lamp and a fan to cool it. On top of the box is a large fresnel lens that collimates the light...
s, projection
televisionTelevision is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
s, and hand-held sheet
magnifying glassA magnifying glass is a convex lens that is used to produce a magnified image of an object. The lens is usually mounted in a frame with a handle ....
es. Fresnel lenses have been used to increase the visual size of
CRTThe cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
displays in pocket
televisionTelevision is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
s, notably the Sinclair
TV80The Sinclair TV80, also known as the Flat Screen Pocket TV or FTV1, was a pocket television launched by Sinclair Research in 1984. Unlike Sinclair's earlier attempts at a portable television, the TV80 used a flat CRT with a side-mounted electron gun instead of a conventional CRT; the picture was...
. They are also used in
traffic lightTraffic lights, which may also be known as stoplights, traffic lamps, traffic signals, signal lights, robots or semaphore, are signalling devices positioned at road intersections, pedestrian crossings and other locations to control competing flows of traffic...
s. Fresnel lenses are also used to correct several visual disorders, including several ocular-motility disorders such as
strabismusStrabismus is a condition in which the eyes are not properly aligned with each other. It typically involves a lack of coordination between the extraocular muscles, which prevents bringing the gaze of each eye to the same point in space and preventing proper binocular vision, which may adversely...
.
Since plastic Fresnel lenses can be made larger than glass lenses, as well as being much cheaper and lighter, they are used to concentrate sunlight for heating in
solar cookerA solar cooker, or solar oven, is a device which uses the energy of sunlight to heat food or drink to cook it or sterilize it. High-tech versions, for example electric ovens powered by solar cells, are possible, and have some advantages such as being able to work in diffuse light. However at...
s, in solar forges, and in solar collectors used to heat water for domestic use.
Perhaps the most widespread use of Fresnel lenses, for a time, was in
automobileAn automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
headlampA headlamp is a lamp, usually attached to the front of a vehicle such as a car or a motorcycle, with the purpose of illuminating the road ahead during periods of low visibility, such as darkness or precipitation. Headlamp performance has steadily improved throughout the automobile age, spurred by...
s, where they allow the roughly parallel beam from the parabolic reflector to be shaped to meet requirements for dipped and main beam patterns, often both in the same headlamp unit (such as the European H4 design). For reasons of cost, weight, and impact resistance, newer cars have dispensed with glass Fresnel lenses, using multifaceted reflectors with plain
polycarbonatePolycarbonatePhysical 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%...
lenses. However, Fresnel lenses continue to be widely used in automobile tail, marker, and backup lights.
Fresnel lenses are also used in left-hand-drive European
lorries-Transport:* Lorry or truck, a large motor vehicle* Lorry, or a Mine car in USA: an open gondola with a tipping trough* Lorry , a horse-drawn low-loading trolley-In fiction:...
entering the UK and Republic of Ireland (and vice versa, right-hand-drive Irish and British trucks entering mainland Europe) to overcome the blind spots caused by the driver operating the lorry while sitting on the "wrong" side of the cab and driving on the "wrong" side of the road. They are applied to the passenger-side window.
High-quality glass Fresnel lenses were used in lighthouses, where they were considered state of the art in the late 19th and through the middle of the 20th centuries; most are now retired from service. Lighthouse Fresnel lens systems typically include extra annular
prismaticIn optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use...
elements, arrayed in faceted domes above and below the central planar Fresnel, in order to catch all light emitted from the light source. The light path through these elements can include an internal reflection, rather than the simple
refractionRefraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The phenomenon is mainly in governance to the law of conservation of energy. The proper explanation would be that due to change of medium, the phase velocity of the wave is changed...
in the planar Fresnel element. These lenses conferred many practical benefits upon the designers, builders, and users of lighthouses and their illumination. Among other things, smaller lenses could fit into more compact spaces. Greater light transmission over longer distances, and varied patterns, made it possible to triangulate a position.
Glass Fresnel lenses also are used in lighting instruments for
theatreTheatre is a collaborative form of fine art that uses live performers to present the experience of a real or imagined event before a live audience in a specific place. The performers may communicate this experience to the audience through combinations of gesture, speech, song, music or dance...
and motion pictures (see
Fresnel lanternA Fresnel lantern is a common lantern used in theatre, which employs a Fresnel lens to wash light over an area of the stage. The lens produces a wider, soft-edged beam of light, which is commonly used for back light and top light....
); such instruments are often called simply
Fresnels. The entire instrument consists of a metal housing, a reflector, a lamp assembly, and a Fresnel lens. Many Fresnel instruments allow the lamp to be moved relative to the lens'
focal pointIn geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by...
, to increase or decrease the size of the light beam.. As a result, they are very flexible, and can often produce a beam as narrow as 7° or as wide as 70°. The Fresnel lens produces a very soft-edged beam, so is often used as a wash light. A holder in front of the lens can hold a colored plastic film (
gel) to tint the light or wire screens or frosted plastic to diffuse it. The Fresnel lens is useful in the making of motion pictures not only because of its ability to focus the beam brighter than a typical lens, but also because the light is a relatively consistent intensity across the entire width of the beam of light.
Aircraft carrierAn aircraft carrier is a warship designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase. Aircraft carriers thus allow a naval force to project air power worldwide without having to depend on local bases for staging aircraft operations...
s and naval air stations typically use Fresnel lenses in their
optical landing systemAn optical landing system is used to give glidepath information to pilots in the terminal phase of landing on an aircraft carrier...
s. The "meatball" light aids the pilot in maintaining proper glide slope for the landing. In the center are amber and red lights composed of Fresnel lenses. Although the lights are always on, the angle of the lens from the pilot's point of view determines the color and position of the visible light. If the lights appear above the green horizontal bar, the pilot is too high. If it is below, the pilot is too low, and if the lights are red, the pilot is very low.
New applications have appeared in solar energy, where Fresnel lenses are used to concentrate sunlight (with a ratio of almost 500:1) onto
solar cellA solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....
s. Thus the active solar cell surface can be reduced to a fraction compared to conventional solar modules. This offers a considerable cost-saving potential by low material consumption, and it is possible to use high-quality and expensive solar cells, which achieve a very high efficiency under concentration due to thermodynamic effects.
Fresnel
reflectors are also currently being incorporated into next-generation solar thermal-energy systems. See
solar powerSolar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...
for more information.
In
photographyPhotography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
, Canon developed a diffractive optics (DO) version of its
EF 70-300mm lensThe EF 70-300mm lens is a telephoto zoom lens made by Canon Inc.The lens has an EF mount to work with the EOS line of cameras.Three Canon EF telephoto zoom lenses carry the 70-300mm designation. These are the EF 70-300mm 4.5-5.6 DO IS USM, EF 70-300mm 4-5.6L IS USM and the EF 70-300mm 4-5.6 IS USM...
using Fresnel lenses. Also, the
Polaroid SX-70The SX-70 is a folding single lens reflex Land Camera which was produced by the Polaroid Corporation from 1972-1981.- History :Though Polaroid had considered a Henry Dreyfus-designed SLR for its Colorpack film, the SX-70 was the first instant SLR and the first camera to use Polaroid's new SX-70...
camera used a Fresnel reflector as part of its viewing system.
Multi-focal Fresnel lenses are also used as a part of
retina identificationA retinal scan is a biometric technique that uses the unique patterns on a person's retina to identify them. It is not to be confused with another ocular-based technology, iris recognition.-Introduction:...
cameras, where they provide multiple in- and out-of-focus images of a fixation target inside the camera. For virtually all users, at least one of the images will be in focus, thus allowing correct eye alignment.
The Fresnel lens has seen applications for enhancing passenger reading lights on Airbus aircraft: in a dark cabin, the focused beam of light does not dazzle neighbouring passengers.
Fresnel lenses have also been used in the field of popular entertainment. The British rock artist
Peter GabrielPeter Brian Gabriel is an English singer, musician, and songwriter who rose to fame as the lead vocalist and flautist of the progressive rock group Genesis. After leaving Genesis, Gabriel went on to a successful solo career...
made use of them in his early solo live performances to magnify the size of his head, in contrast to the rest of his body, for dramatic and comic effect. In the
Terry GilliamTerrence Vance "Terry" Gilliam is an American-born British screenwriter, film director, animator, actor and member of the Monty Python comedy troupe. Gilliam is also known for directing several films, including Brazil , The Adventures of Baron Munchausen , The Fisher King , and 12 Monkeys...
film
BrazilBrazil is a 1985 British science fiction fantasy/black comedy film directed by Terry Gilliam. It was written by Gilliam, Charles McKeown, and Tom Stoppard and stars Jonathan Pryce. The film also features Robert De Niro, Kim Greist, Michael Palin, Katherine Helmond, Bob Hoskins, and Ian Holm...
, plastic Fresnel screens appear ostensibly as magnifiers for the small CRT monitors used throughout the offices of the Ministry of Information. However, they occasionally appear between the actors and the camera, distorting the scale and composition of the scene to humorous effect.
Projection uses
Fresnel lenses of different focal lengths (one
collimatorA collimator is a device that narrows a beam of particles or waves. To "narrow" can mean either to cause the directions of motion to become more aligned in a specific direction or to cause the spatial cross section of the beam to become smaller.- Optical collimators :In optics, a collimator may...
, and one collector) are used in commercial and DIY projection. The collimator lens has the lower focal length and is placed closer to the light source, and the collector lens, which focuses the light into the triplet lens, is placed after the projection image (an active matrix LCD panel in
LCD projectorAn LCD projector is a type of video projector for displaying video, images or computer data on a screen or other flat surface. It is a modern equivalent of the slide projector or overhead projector...
s). Fresnel lenses are also used as collimators in
overhead projectorAn overhead projector is a variant of slide projector that is used to display images to an audience.-Mechanism:An overhead projector typically consists of a large box containing a very bright lamp and a fan to cool it. On top of the box is a large fresnel lens that collimates the light...
s.
Generating solar power
More recently Fresnel reflectors are used in concentrating solar power (CSP) plants to concentrate solar energy.
Interstellar Travel
Fresnel lenses, hundreds of kilometers in diameter and placed in the outer solar system, have been suggested as a method of concentrating the energy from a giant solar-powered
maserA maser is a device that produces coherent electromagnetic waves through amplification by stimulated emission. Historically, “maser” derives from the original, upper-case acronym MASER, which stands for "Microwave Amplification by Stimulated Emission of Radiation"...
or
laserA 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...
onto a distant
solar sailSolar sails are a form of spacecraft propulsion using the radiation pressure of light from a star or laser to push enormous ultra-thin mirrors to high speeds....
, pushing it to distances of up to forty light years.
Further reading
- "The Fresnel Lens." The Keeper's Log (Winter 1985), pp. 12–14.
- Lighthouses, Illuminants, Lenses Engineering and Augustin Fresnel, An Historical Bibliography, United States Coast Guard.
- United States Coast Guard
The United States Coast Guard is a branch of the United States Armed Forces and one of the seven U.S. uniformed services. The Coast Guard is a maritime, military, multi-mission service unique among the military branches for having a maritime law enforcement mission and a federal regulatory agency...
, Aids to Navigation, (Washington, DC: U. S. Government Printing Office, 1945).
- United States Coast Guard, Fresnel Lenses Still in Operation.
External links