Incandescent light bulb
Encyclopedia
Incandescence
Incandescence is the emission of light from a hot body as a result of its temperature. The term derives from the Latin verb incandescere, to glow white....
. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp
Halogen lamp
A halogen lamp, also known as a tungsten halogen lamp, is an incandescent lamp with a tungsten filament contained within an inert gas and a small amount of a halogen such as iodine or bromine. The chemical halogen cycle redeposits evaporated tungsten back on to the filament, extending the life of...
, a chemical process returns metal to the filament, extending its life. The light bulb is supplied with electrical current by feed-through terminals or wires embedded in the glass. Most bulbs are used in a socket which provides mechanical support and electrical connections.
Incandescent bulbs are produced in a wide range of sizes, light output, and voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
ratings, from 1.5 volts to about 300 volts. They require no external regulating equipment, have low manufacturing cost
Manufacturing cost
Manufacturing cost is the sum of costs of all resources consumed in the process of making a product. The manufacturing cost is classified into three categories: direct materials cost, direct labor cost and manufacturing overhead.- Direct materials cost :...
s, and work equally well on either alternating current or direct current. As a result, the incandescent lamp is widely used in household and commercial lighting, for portable lighting such as table lamps, car headlamp
Headlamp
A 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, and flashlight
Flashlight
A flashlight is a hand-held electric-powered light source. Usually the light source is a small incandescent lightbulb or light-emitting diode...
s, and for decorative and advertising lighting.
Some applications of the incandescent bulb use the heat generated by the filament, such as incubators, brooding boxes for poultry
Poultry
Poultry are domesticated birds kept by humans for the purpose of producing eggs, meat, and/or feathers. These most typically are members of the superorder Galloanserae , especially the order Galliformes and the family Anatidae , commonly known as "waterfowl"...
, heat lights for 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...
tanks, infrared heating
Infrared heater
An infrared heater is a body with a higher temperature which transfers energy to a body with a lower temperature through electromagnetic radiation. Depending on the temperature of the emitting body, the wavelength of the infrared radiation ranges from 780 nm to 1 mm. The relationship...
for industrial heating and drying processes, and the Easy-Bake Oven
Easy-Bake Oven
The Easy-Bake Oven is a working toy oven introduced by Kenner in 1963, and currently manufactured by Hasbro. The original toy used an ordinary incandescent light bulb as a heat source; current versions use a true heating element. By 1997, more than 16 million Easy-Bake Ovens had been sold.The...
toy. This waste heat increases the energy required by a building's air conditioning
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
system.
Incandescent light bulbs are gradually being replaced in many applications by other types of electric light
Electric light
Electric lights are a convenient and economic form of artificial lighting which provide increased comfort, safety and efficiency. Most electric lighting is powered by centrally-generated electric power, but lighting may also be powered by mobile or standby electric generators or battery systems...
s, such as 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, compact fluorescent lamp
Compact fluorescent lamp
A compact fluorescent lamp , also called compact fluorescent light, energy-saving light, and compact fluorescent tube, is a fluorescent lamp designed to replace an incandescent lamp; some types fit into light fixtures formerly used for incandescent lamps...
s (CFL), cold cathode fluorescent lamps (CCFL), high-intensity discharge lamp
High-intensity discharge lamp
High-intensity discharge lamps are a type of electrical lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. This tube is filled with both gas and metal salts. The gas facilitates the...
s, and light-emitting diode
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...
s (LEDs). These newer technologies improve the ratio of visible light to heat generation. Some jurisdictions, such as the European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...
, are in the process of phasing out the use of incandescent light bulbs in favor of more energy-efficient lighting.
History of the light bulb
Joseph Swan
Sir Joseph Wilson Swan was a British physicist and chemist, most famous for the invention of the incandescent light bulb for which he received the first patent in 1878...
and Thomas Edison
Thomas Edison
Thomas Alva Edison was an American inventor and businessman. He developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, practical electric light bulb. In addition, he created the world’s first industrial...
. They conclude that Edison's version was able to outstrip the others because of a combination of three factors: an effective incandescent material, a higher 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...
than others were able to achieve (by use of the Sprengel pump
Sprengel pump
The Sprengel pump is a vacuum pump invented by Hanover-born chemist Hermann Sprengel in 1865 while he was working in London. The pump created the highest vacuum achievable at that time....
) and a high resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
that made power distribution from a centralized source economically viable.
Another historian, Thomas Hughes, has attributed Edison's success to the fact that he developed an entire, integrated system of electric lighting.
The lamp was a small component in his system of electric lighting, and no more critical to its effective functioning than the Edison Jumbo generator
Electrical generatorIn electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow...
, the Edison main and feeder, and the parallel-distribution system. Other inventors with generators and incandescent lamps, and with comparable ingenuity and excellence, have long been forgotten because their creators did not preside over their introduction in a system of lightingLightingLighting or illumination is the deliberate application of light to achieve some practical or aesthetic effect. Lighting includes the use of both artificial light sources such as lamps and light fixtures, as well as natural illumination by capturing daylight...
.
Historian Thomas P. Hughes
| Early evolution of the light bulb | |
|---|---|
Early pre-commercial research
In 1802, Humphry DavyHumphry Davy
Sir Humphry Davy, 1st Baronet FRS MRIA was a British chemist and inventor. He is probably best remembered today for his discoveries of several alkali and alkaline earth metals, as well as contributions to the discoveries of the elemental nature of chlorine and iodine...
had what was then the most powerful electrical battery
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
in the world at the Royal Institution
Royal Institution
The Royal Institution of Great Britain is an organization devoted to scientific education and research, based in London.-Overview:...
of Great Britain. In that year, he created the first incandescent light by passing the current through a thin strip of platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
, chosen because the metal had an extremely high melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...
. It was not bright enough nor did it last long enough to be practical, but it was the precedent behind the efforts of scores of experimenters over the next 75 years. In 1809, Davy also created the first arc lamp
Arc lamp
"Arc lamp" or "arc light" is the general term for a class of lamps that produce light by an electric arc . The lamp consists of two electrodes, first made from carbon but typically made today of tungsten, which are separated by a gas...
with two carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
charcoal
Charcoal
Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...
rods connected to a 2000-cell battery; it was demonstrated to the Royal Institution in 1810.
Over the first three-quarters of the 19th century many experimenters worked with various combinations of platinum or iridium wires, carbon rods, and evacuated or semi-evacuated enclosures. Many of these devices were demonstrated and some were patented.
In 1835, James Bowman Lindsay
James Bowman Lindsay
James Bowman Lindsay was a Scottish inventor and author. He is credited with early developments in several fields, such as incandescent lighting and telegraphy.- Life and work :...
demonstrated a constant electric light at a public meeting in Dundee, Scotland. He stated that he could "read a book at a distance of one and a half feet". However, having perfected the device to his own satisfaction, he turned to the problem of wireless telegraphy
Wireless telegraphy
Wireless telegraphy is a historical term used today to apply to early radio telegraph communications techniques and practices, particularly those used during the first three decades of radio before the term radio came into use....
and did not develop the electric light any further. His claims are not well documented, although he is credited in Challoner etal. with being the inventor of the "Incandescent Light Bulb".
In 1840, British scientist Warren de la Rue
Warren de la Rue
Warren De la Rue was a British astronomer and chemist, most famous for his pioneering work in astronomical photography.-Biography:...
enclosed a coil
Coil
A coil is a series of loops. A coiled coil is a structure in which the coil itself is in turn also looping.-Electromagnetic coils:An electromagnetic coil is formed when a conductor is wound around a core or form to create an inductor or electromagnet...
ed platinum filament 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...
tube and passed an electric current through it. The design was based on the concept that the high melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...
of platinum would allow it to operate at high temperatures and that the evacuated chamber would contain fewer gas molecules to react with the platinum, improving its longevity. Although an efficient design, the cost of the platinum made it impractical for commercial use.
In 1841, Frederick de Moleyns of England was granted the first patent
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....
for an incandescent lamp, with a design using platinum wires contained within a vacuum bulb.
In 1845, American John W. Starr
John Wellington Starr
John Wellington Starr was an American inventor and pioneer in development of the incandescent light bulb. Starr was born in Cincinnati. In 1844, in association with John Milton Sanders , Starr filed a U. S. patent caveat for an incandescent lamp and generator.Starr appears never to have...
acquired a patent for his incandescent light bulb involving the use of carbon filaments.
He died shortly after obtaining the patent, and his invention was never produced commercially. Little else is known about him.
In 1851, Jean Eugène Robert-Houdin
Jean Eugène Robert-Houdin
Jean Eugène Robert-Houdin was a French magician. He is widely considered the father of the modern style of conjuring.-Early life and entrance into conjuring:...
publicly demonstrated incandescent light bulbs on his estate in Blois, France. His light bulbs are on permanent display in the museum of the Château de Blois
Château de Blois
The Royal Château de Blois is located in the Loir-et-Cher département in the Loire Valley, in France, in the center of the city of Blois. The residence of several French kings, it is also the place where Joan of Arc went in 1429 to be blessed by the Archbishop of Reims before departing with her...
.
In 1872, Russian Alexander Lodygin invented an incandescent light bulb and obtained a Russian patent in 1874. He used as a burner two carbon rods of diminished section in a glass receiver, hermetically sealed, and filled with nitrogen, electrically arranged so that the current could be passed to the second carbon when the first had been consumed.
Later he lived in the USA, changed his name to Alexander de Lodyguine and applied and obtained patents for incandescent lamps having chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
, iridium
Iridium
Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...
, rhodium
Rhodium
Rhodium is a chemical element that is a rare, silvery-white, hard and chemically inert transition metal and a member of the platinum group. It has the chemical symbol Rh and atomic number 45. It is composed of only one isotope, 103Rh. Naturally occurring rhodium is found as the free metal, alloyed...
, ruthenium
Ruthenium
Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element...
, osmium
Osmium
Osmium is a chemical element with the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-blacktransition metal in the platinum family, and is the densest natural element. Osmium is twice as dense as lead. The density of osmium is , slightly greater than that of iridium,...
, molybdenum
Molybdenum
Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...
and tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
filaments,, and a bulb using a molybdenum filament was demonstrated at the world fair
Exposition Universelle (1900)
The Exposition Universelle of 1900 was a world's fair held in Paris, France, from April 15 to November 12, 1900, to celebrate the achievements of the past century and to accelerate development into the next...
of 1900 in Paris
Paris
Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...
.
Heinrich Göbel
Heinrich Göbel
Heinrich Göbel, later Henry Goebel , born in Springe, Germany, was a precision mechanic. He emigrated in 1848 to New York City and lived there until his death. In 1865 he changed his nationality....
in 1893 claimed he had designed the first incandescent light bulb in 1854, with a thin carbonized bamboo
Bamboo
Bamboo is a group of perennial evergreens in the true grass family Poaceae, subfamily Bambusoideae, tribe Bambuseae. Giant bamboos are the largest members of the grass family....
filament of high resistance, platinum lead-in wires in an all-glass envelope, and a high vacuum. Judges of four courts raised doubts about the alleged Goebel anticipation, but there was never a decision in a final hearing due to the expiry date of Edison's patent. A research work published 2007 concluded that the story of the Goebel lamps in the 1850s is a legend.
On July 24, 1874, a Canadian
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
patent
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....
was filed by Henry Woodward
Henry Woodward (inventor)
Henry Woodward was a Canadian inventor and a major pioneer in the development of the incandescent lamp.-Work on the incandescent light bulb:On July 24, 1874, Woodward and his partner, Mathew Evans, a hotel keeper, patented an electric light bulb. Woodward was a medical student at the time. Their...
and Mathew Evans
Mathew Evans
Mathew Evans is one of two Canadians who developed and patented an incandescent light bulb, on July 24, 1874, five years before Thomas Alva Edison's U.S...
for a lamp consisting of carbon rods mounted in a nitrogen-filled glass cylinder. They were unsuccessful at commercializing their lamp, and sold rights to their patent to Thomas Edison in 1879.
Commercialization
Joseph Swan
Sir Joseph Wilson Swan was a British physicist and chemist, most famous for the invention of the incandescent light bulb for which he received the first patent in 1878...
(1828–1914) was a British physicist and chemist. In 1850, he began working with carbonized paper filaments in an evacuated glass bulb. By 1860, he was able to demonstrate a working device but the lack of a good vacuum and an adequate supply of electricity resulted in a short lifetime for the bulb and an inefficient source of light. By the mid-1870s better pumps became available, and Swan returned to his experiments.
With the help of Charles Stearn, an expert on vacuum pumps, in 1878, Swan developed a method of processing that avoided the early bulb blackening. This received British Patent No 8 in 1880. On 18 December 1878, a lamp using a slender carbon rod was shown at a meeting of the Newcastle Chemical Society, and Swan gave a working demonstration at their meeting on 17 January 1879. It was also shown to 700 who attended a meeting of the Literary and Philosophical Society of Newcastle upon Tyne on 3 February 1879. These lamps used a carbon rod from an arc lamp rather than a slender filament. Thus they had low resistance and required very large conductors to supply the necessary current, so they were not commercially practical, although they did furnish a demonstration of the possibilities of incandescent lighting with relatively high vacuum, a carbon conductor, and platinum lead-in wires. Besides requiring too much current for a central station electric system to be practical, they had a very short lifetime. Swan turned his attention to producing a better carbon filament and the means of attaching its ends. He devised a method of treating cotton to produce 'parchmentised thread' and obtained British Patent 4933 in 1880. From this year he began installing light bulbs in homes and landmarks in England. His house was the first in the world to be lit by a lightbulb and so the first house in the world to be lit by hydroelectric power. In the early 1880s he had started his company. In 1881, the Savoy Theatre
Savoy Theatre
The Savoy Theatre is a West End theatre located in the Strand in the City of Westminster, London, England. The theatre opened on 10 October 1881 and was built by Richard D'Oyly Carte on the site of the old Savoy Palace as a showcase for the popular series of comic operas of Gilbert and Sullivan,...
in the City of Westminster
City of Westminster
The City of Westminster is a London borough occupying much of the central area of London, England, including most of the West End. It is located to the west of and adjoining the ancient City of London, directly to the east of the Royal Borough of Kensington and Chelsea, and its southern boundary...
, London was lit by Swan incandescent lightbulbs, which was the first theatre, and the first public building in the world, to be lit entirely by electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
.
Thomas Edison
Thomas Edison
Thomas Alva Edison was an American inventor and businessman. He developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, practical electric light bulb. In addition, he created the world’s first industrial...
began serious research into developing a practical incandescent lamp in 1878. Edison filed his first patent application for "Improvement In Electric Lights" on October 14, 1878. After many experiments with platinum and other metal filaments, Edison returned to a carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
filament. The first successful test was on October 22, 1879, and lasted 13.5 hours. Edison continued to improve this design and by November 4, 1879, filed for a U.S. patent for an electric lamp using "a carbon filament or strip coiled and connected ... to platina contact wires." Although the patent described several ways of creating the carbon filament including using "cotton and linen thread, wood splints, papers coiled in various ways," it was not until several months after the patent was granted that Edison and his team discovered that a carbonized bamboo filament could last over 1200 hours.
Hiram S. Maxim started a lightbulb company in 1878 to exploit his patents and those of William Sawyer
William E. Sawyer
William Edward Sawyer was an American inventor whose contribution was primarily in the field of electric engineering and electric lighting.His primary inventions included:* Telegraph apparatus for cable use...
. His United States Electric Lighting Company was the second company, after Edison, to sell practical incandescent electric lamps. They made their first commercial installation of incandescent lamps at the Mercantile Safe Deposit Company in New York City
New York City
New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...
in the fall of 1880, about six months after the Edison incandescent lamps had been installed on the steamer Columbia. In October 1880, Maxim patented a method of coating carbon filaments with 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 to extend their life. Lewis Latimer, his employee at the time, developed an improved method of heat-treating them which reduced breakage and allowed them to be molded into novel shapes, such as the characteristic "M" shape of Maxim filaments. On January 17, 1882, Latimer received a patent for the "Process of Manufacturing Carbons," an improved method for the production of light bulb filaments, which was purchased by the United States Electric Light Company. Latimer patented other improvements such as a better way of attaching filaments to their wire supports.
In Britain
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, the Edison and Swan companies merged into the Edison and Swan United Electric Company (later known as Ediswan, that was ultimately incorporated into Thorn Lighting Ltd). Edison was initially against this combination, but after Swan sued him and won, Edison was eventually forced to cooperate, and the merger was made. Eventually, Edison acquired all of Swan's interest in the company. Swan sold his United States patent rights to the Brush Electric Company in June 1882.
Christmas tree
The Christmas tree is a decorated evergreen coniferous tree, real or artificial, and a tradition associated with the celebration of Christmas. The tradition of decorating an evergreen tree at Christmas started in Livonia and Germany in the 16th century...
was installed. These did not become common in homes for many years.
The United States Patent Office
United States Patent and Trademark Office
The United States Patent and Trademark Office is an agency in the United States Department of Commerce that issues patents to inventors and businesses for their inventions, and trademark registration for product and intellectual property identification.The USPTO is based in Alexandria, Virginia,...
gave a ruling October 8, 1883, that Edison's patents were based on the prior art of William Sawyer
William E. Sawyer
William Edward Sawyer was an American inventor whose contribution was primarily in the field of electric engineering and electric lighting.His primary inventions included:* Telegraph apparatus for cable use...
and were invalid. Litigation continued for a number of years. Eventually on October 6, 1889, a judge ruled that Edison's electric light improvement claim for "a filament of carbon of high resistance" was valid.
In the 1890s, the Austrian inventor Carl Auer von Welsbach
Carl Auer von Welsbach
Carl Auer Freiherr von Welsbach was an Austrian scientist and inventor who had a talent for not only discovering advances, but turning them into commercially successful products...
worked on metal-filament mantles, first with platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
wire, and then osmium
Osmium
Osmium is a chemical element with the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-blacktransition metal in the platinum family, and is the densest natural element. Osmium is twice as dense as lead. The density of osmium is , slightly greater than that of iridium,...
, and produced an operating version in 1898. In 1898, he patented the osmium lamp and started marketing it in 1902, the first commercial metal filament incandescent lamp.
In 1897, German physicist and chemist Walther Nernst
Walther Nernst
Walther Hermann Nernst FRS was a German physical chemist and physicist who is known for his theories behind the calculation of chemical affinity as embodied in the third law of thermodynamics, for which he won the 1920 Nobel Prize in chemistry...
developed the Nernst lamp
Nernst lamp
Nernst lamps were an early form of electrically powered incandescent lamps. Nernst lamps did not use a glowing tungsten filament. Instead, they used a ceramic rod that was heated to incandescence...
, a form of incandescent lamp that used a ceramic globar
Globar
A Globar is a silicon carbide rod of 5 to 10 mm width and 20 to 50 mm length which is electrically heated up to . When combined with a downstream variable interference filter, it emits radiation from 4 to 15 micrometres wavelength...
and did not require enclosure in a vacuum or inert gas. Twice as efficient as carbon filament lamps, Nernst lamps were briefly popular until overtaken by lamps using metal filaments.
In 1901, American businessman Frank A. Poor purchased the Merritt Manufacturing Company, the predecessor to North American light bulb makers Hygrade and Osram Sylvania
Osram Sylvania
Osram Sylvania Inc. is the North American operation of lighting manufacturer Osram GmbH, which is owned by Siemens AG. It was established in January 1993, with the acquisition of GTE’s Sylvania lighting division by Osram GmbH....
. Poor's firm in Middleton, Massachusetts
Middleton, Massachusetts
Middleton is a town in Essex County, Massachusetts, United States. The population was 8,987 at the 2010 census.- History :Middleton was first settled in 1659 and was officially incorporated in 1728. Prior to 1728 it was considered a part of Salem, and contains territory previously within the...
, specialized in refilling burned-out light bulbs until 1916.
In 1903, Willis Whitnew invented a metal-coated carbon filament that would not blacken the inside of a light bulb.
On December 13, 1904, Hungarian
Hungary
Hungary , officially the Republic of Hungary , is a landlocked country in Central Europe. It is situated in the Carpathian Basin and is bordered by Slovakia to the north, Ukraine and Romania to the east, Serbia and Croatia to the south, Slovenia to the southwest and Austria to the west. The...
Sándor Just and Croatian
Croats
Croats are a South Slavic ethnic group mostly living in Croatia, Bosnia and Herzegovina and nearby countries. There are around 4 million Croats living inside Croatia and up to 4.5 million throughout the rest of the world. Responding to political, social and economic pressure, many Croats have...
Franjo Hanaman were granted a Hungarian patent (No. 34541) for a tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
filament lamp, that lasted longer and gave a brighter light than the carbon filament. Tungsten filament lamps were first marketed by the Hungarian
Hungary
Hungary , officially the Republic of Hungary , is a landlocked country in Central Europe. It is situated in the Carpathian Basin and is bordered by Slovakia to the north, Ukraine and Romania to the east, Serbia and Croatia to the south, Slovenia to the southwest and Austria to the west. The...
company Tungsram
Tungsram
Tungsram is a Hungarian manufacturer of light bulbs and vacuum tubes since 1896. General Electric, in 1990, acquired majority share in one of Hungary's largest, oldest, and internationally most prestigious firms, the light-source manufacturer Tungsram. Over the past six years GE has invested $600...
in 1904, so this type is often called Tungsram-bulbs in many European countries. Their experiments also showed that the luminosity of bulbs that were filled up with an inert gas
Inert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...
was higher. The tungsten filament outlasted all other types.
In 1906, the General Electric Company
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
patented a method of making filaments from sintered tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
and in 1911, used ductile tungsten wire for incandescent light bulbs.
In 1913, Irving Langmuir
Irving Langmuir
Irving Langmuir was an American chemist and physicist. His most noted publication was the famous 1919 article "The Arrangement of Electrons in Atoms and Molecules" in which, building on Gilbert N. Lewis's cubical atom theory and Walther Kossel's chemical bonding theory, he outlined his...
found that filling a lamp with inert gas
Inert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...
instead of a vacuum resulted in twice the luminous efficacy and reduction of bulb blackening. In 1924, Marvin Pipkin
Marvin Pipkin
Marvin Pipkin , American chemist and inventor of two processes for inside frosting of incandescent lamp bulbs.Born near Lakeland, Florida, Pipkin attended Alabama Polytechnic Institute and received a Batchelor of Science degree in Chemical Engineering in 1913 and a Master's in 1915. In 1917 Pipkin...
, an American chemist, patented a process for frost
Frosting (decorative arts)
A decorative art technique based on the climatatogical nature of frost is the technique of Frosting.-Examples of ancient Egyptian steles:Eventually Ancient Egyptian steles became more than just statements about a topic or events, and became a means of decoration. Later period steles were made in...
ing the inside of lamp bulbs without weakening them, and in 1947, he patented a process for coating the inside of lamps with silica.
In 1930, Hungarian
Hungary
Hungary , officially the Republic of Hungary , is a landlocked country in Central Europe. It is situated in the Carpathian Basin and is bordered by Slovakia to the north, Ukraine and Romania to the east, Serbia and Croatia to the south, Slovenia to the southwest and Austria to the west. The...
Imre Bródy
Imre Bródy
Imre Bródy , a Hungarian physicist, who invented in 1930 the krypton-filled fluorescent lamps ,...
filled lamps with krypton gas rather than argon, and designed a process to obtain krypton from air. Production of krypton filled lamps based on his invention started at Ajka
Ajka
Ajka is a city in Hungary with about 35,000 inhabitants. It is situated in the hills of Bakony.-History:Around 1000 BCE the area was inhabited by Celts. By the 2nd century CE the territory was conquered by the Romans...
in 1937, in a factory co-designed by Polányi and Hungarian-born physicist Egon Orowan
Egon Orowan
Egon Orowan was a Hungarian/British/U.S. physicist and metallurgist.-Life:Orowan was born in the Óbuda district of Budapest. His father, Berthold, was a mechanical engineer and factory manager, and his mother, Josze Spitzer Ságvári was the daughter of an impoverished land owner...
.
By 1964, improvements in efficiency and production of incandescent lamps had reduced the cost of providing a given quantity of light by a factor of thirty, compared with the cost at introduction of Edison's lighting system
Consumption of incandescent light bulbs grew rapidly in the United States. In 1885, an estimated 300,000 general lighting service lamps were sold, all with carbon filaments. When tungsten filament were introduced, there were about 50 million lamp sockets in the United States. In 1914, 88.5 million lamps were used, (only 15% with carbon filaments), and by 1945, annual sales of lamps were 795 million (more than 5 lamps per person per year).
Cartels
Between 1924 and 1939, the international market for incandescent light bulbs was controlled by the Phoebus cartel, which dictated wholesale prices and whose members controlled most of the world market for lamps.Efficiency and environmental impact
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
, rather than as visible light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
.
Luminous efficacy
Luminous efficacy
Luminous efficacy is a measure of how well a light source produces visible light. It is the ratio of luminous flux to power. Depending on context, the power can be either the radiant flux of the source's output, or it can be the total electric power consumed by the source.Which sense of the term is...
of a light source is a ratio of the visible light energy emitted (the luminous flux) to the total power input to the lamp. Visible light is measured in lumens
Lumen (unit)
The lumen is the SI derived unit of luminous flux, a measure of the total "amount" of visible light emitted by a source. Luminous flux differs from power in that luminous flux measurements reflect the varying sensitivity of the human eye to different wavelengths of light, while radiant flux...
, a unit which is defined in part by the differing sensitivity of the human eye to different wavelengths of light. Not all wavelengths of visible electromagnetic energy are equally effective at stimulating the human eye; the luminous efficacy of radiant energy is a measure of how well the distribution of energy matches the perception of the eye. The maximum efficacy possible is 683 lm/W for monochromatic green light at 555 nanometres wavelength, the peak sensitivity of the human eye. For white light, the maximum luminous efficacy is around 240 lumens per watt, but the exact value is not unique because the human eye can perceive many different mixtures of visible light as "white".
The chart below lists values of overall luminous efficacy and efficiency for several types of general service, 120-volt, 1000-hour lifespan incandescent bulb, and several idealized light sources. A similar chart in the article on luminous efficacy compares a broader array of light sources to one another.
| Type | Overall luminous efficiency | Overall luminous efficacy (lm/W) |
|---|---|---|
| 40 W tungsten incandescent | 1.9% | 12.6 |
| 60 W tungsten incandescent | 2.1% | 14.5 |
| 100 W tungsten incandescent | 2.6% | 17.5 |
| glass halogen | 2.3% | 16 |
| quartz halogen | 3.5% | 24 |
| high-temperature incandescent | 5.1% | 35 |
| ideal black-body radiator at 4000 K (or a class Stellar classification In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure... K star like Arcturus) |
7.0% | 47.5 |
| ideal black-body radiator at 7000 K (or a class Stellar classification In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure... F star like Procyon Procyon Procyon is the brightest star in the constellation Canis Minor. To the naked eye, it appears to be a single star, the seventh brightest in the night sky with a visual apparent magnitude of 0.34... ) |
14% | 95 |
| ideal monochromatic 555 nm (green) source | 100% | 683 |
Unfortunately, the spectrum emitted by a blackbody radiator does not match the sensitivity characteristics of the human eye. Tungsten filaments radiate mostly infrared radiation at temperatures where they remain solid (below 3683 kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
s / 3410 °C / 6,170 °F). Donald L. Klipstein explains it this way: "An ideal thermal radiator produces visible light most efficiently at temperatures around 6300 °C (6600 K or 11,500 °F). Even at this high temperature, a lot of the radiation is either infrared or ultraviolet, and the theoretical luminous efficiency is 95 lumens per watt." No known material can be used as a filament at this ideal temperature, which is hotter than the sun's surface. An upper limit for incandescent lamp luminous efficacy is around 52 lumens per watt, the theoretical value emitted by tungsten at its melting point.
For a given quantity of light, an incandescent light bulb produces more heat (and consumes more power) than a 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...
. In buildings where air conditioning
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
is used, incandescent lamps' heat output increases load on the air conditioning system. Heat from lights will displace heat required from a building's heating system; generally space heating energy is of lower cost than electricity.
High-quality halogen incandescent lamps
Halogen lamp
A halogen lamp, also known as a tungsten halogen lamp, is an incandescent lamp with a tungsten filament contained within an inert gas and a small amount of a halogen such as iodine or bromine. The chemical halogen cycle redeposits evaporated tungsten back on to the filament, extending the life of...
have higher efficacy, which will allow a 60-watt bulb to provide nearly as much light as a non-halogen 100-watt bulb. Also, a lower-wattage halogen lamp can be designed to produce the same amount of light as a 60-watt non-halogen lamp, but with much longer life.
Many light sources, such as the 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...
, high-intensity discharge lamp
High-intensity discharge lamp
High-intensity discharge lamps are a type of electrical lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. This tube is filled with both gas and metal salts. The gas facilitates the...
s and LED lamps offer higher efficiency, and some have been designed to be retrofitted in existing fixtures. These devices produce light by luminescence
Luminescence
Luminescence is emission of light by a substance not resulting from heat; it is thus a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light emitted by a...
, instead of heating a filament to incandescence. These mechanisms produce discrete 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 :...
s and so don't have the broad "tail" of wasted invisible infrared emissions produced by incandescent emitters. By careful selection of which electron energy level transitions are used, the spectrum emitted can be tuned to mimic the appearance of incandescent sources, or other different color temperature
Color temperature
Color temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, manufacturing, astrophysics, and other fields. The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of...
s of white light.
Cost of lighting
The initial cost of an incandescent bulb is small compared to the cost of the energy it uses over its lifetime. A comparison of incandescent lamp operating cost with other light sources must consider the luminous efficacy produced by each lamp. The comparison must include illumination requirements, capital cost of the lamp, labor cost to replace lamps, various depreciation factors for light output as the lamp ages, effect of lamp operation on heating and air conditioning systems, and energy consumption as well.Measures to ban its use
Due to the higher energy usage of incandescent light bulbs in comparison to more energy efficient alternatives, such as CFLCompact fluorescent lamp
A compact fluorescent lamp , also called compact fluorescent light, energy-saving light, and compact fluorescent tube, is a fluorescent lamp designed to replace an incandescent lamp; some types fit into light fixtures formerly used for incandescent lamps...
s and LED lamp
LED lamp
An LED lamp is a solid-state lamp that uses light-emitting diodes as the source of light. The LEDs involved may be conventional semiconductor light-emitting diodes, organic LEDs , or polymer light-emitting diodes devices, although PLED technologies are not currently commercially available.Since...
s, many governments have introduced measures to ban their use, by setting minimum efficacy standards higher than can be achieved by general service lamps.
In the United States, federal law has scheduled the most common incandescent light bulbs to be phased out by 2014, to be replaced with more energy-efficient light bulbs. Traditional incandescent light bulbs were phased out in Australia in November 2009.
There has been consumer resistance to phasing out of incandescent lamps, preferring the quality of light produced from incandescents to the principle of free markets, the instant availability of light, and concerns about mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
contamination
Contamination
Contamination is the presence of a minor and unwanted constituent in material, physical body, natural environment, at a workplace, etc.-Specifics:"Contamination" also has more specific meanings in science:...
with CFLs. Varying and unpredictable quality of current CFLs and LED lamps adds to the resistance.
Efforts to improve efficiency
Some research has been carried out to improve the efficacy of commercial incandescent lamps. In 2007, the consumer lighting division of General ElectricGeneral Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
announced a "high efficiency incandescent" (HEI) lamp project, which they claimed would ultimately be as much as four times more efficient than current incandescents, although their initial production goal was to be approximately two times more efficient. The HEI program was quietly terminated in 2008 due to slow progress.
U.S. Department of Energy research at Sandia National Laboratories
Sandia National Laboratories
The Sandia National Laboratories, managed and operated by the Sandia Corporation , are two major United States Department of Energy research and development national laboratories....
initially indicated the potential for dramatically improved efficiency from a photonic lattice filament. However, later work indicated that initially promising results were in error.
Prompted by U.S. legislation mandating increased bulb efficiency by 2012, new "hybrid" incandescent bulbs have been introduced by Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....
. The "Halogena Energy Saver" incandescent is 30 percent more efficient than traditional designs, using a special chamber to reflect formerly wasted heat back to the filament to provide additional lighting power.
Construction
Incandescent light bulbs consist of a glassGlass
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...
enclosure (the envelope, or bulb) with a filament of tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
wire inside the bulb, through which an electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
is passed. Contact wires and a base with two (or more) conductors provide electrical connections to the filament. Incandescent light bulbs usually contain a stem or glass mount anchored to the bulb's base that allows the electrical contacts to run through the envelope without gas/air leaks. Small wires embedded in the stem in turn support the filament and/or its lead wires. The bulb is filled with an inert gas
Inert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...
such as 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...
to reduce evaporation
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
and prevent oxidation of the filament.
An electric current heats the filament to typically 2000 to 3300 K (3,140.3 to 5,480.3 F)), well below tungsten's melting point of 3695 kelvins (6,191.3 °F). Filament temperatures depend on the filament type, shape, size, and amount of current drawn. The heated filament emits light that approximates a continuous spectrum
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...
. The useful part of the emitted energy is visible light, but most energy is given off as heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
in the near-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...
wavelengths.
Three-way light bulbs have two filaments and three conducting contacts in their bases. The filaments share a common ground, and can be lit separately or together. Common wattages include 30–70–100, 50–100–150, and 100–200–300, with the first two numbers referring to the individual filaments, and the third giving the combined wattage.
While most light bulbs have clear or frosted glass, other kinds are also produced, including the various colors used for Christmas tree
Christmas tree
The Christmas tree is a decorated evergreen coniferous tree, real or artificial, and a tradition associated with the celebration of Christmas. The tradition of decorating an evergreen tree at Christmas started in Livonia and Germany in the 16th century...
lights and other decorative lighting. Neodymium
Neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite...
-containing glass is sometimes used to provide a more natural-appearing light.
 |
|
Many arrangements of electrical contacts are used. Large lamps may have a screw base (one or more contacts at the tip, one at the shell) or a bayonet base (one or more contacts on the base, shell used as a contact or used only as a mechanical support). Some tubular lamps have an electrical contact at either end. Miniature lamps may have a wedge base and wire contacts, and some automotive and special purpose lamps have screw terminals for connection to wires. Contacts in the lamp socket allow the electric current to pass through the base to the filament. Power ratings for incandescent light bulbs range from about 0.1 watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
to about 10,000 watts.
The glass bulb of a general service lamp can reach temperatures between 200 and 260 °C (392 and 500 F). Lamps intended for high power operation or used for heating purposes will have envelopes made of hard glass or fused 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,...
.
Manufacturing
Early lamps were laboriously hand-assembled; however, after automatic machinery was developed the cost of lamps fell.In manufacturing the glass bulb, a type of "ribbon machine" is used. A continuous ribbon of glass is passed along a conveyor belt, heated in a furnace, and then blown by precisely aligned air nozzles through holes in the conveyor belt into molds. Thus the glass bulbs are created. After the bulbs are blown, and cooled, they are cut off of the ribbon machine. A typical machine of this sort produces 50,000 bulbs per hour. The filament and its supports are assembled on a glass stem, which is fused to the bulb. The air is pumped out of the bulb, and the evacuation tube in the stem press is sealed by a flame. The bulb is then inserted into the lamp base, and the whole assembly tested.
Filament
The first successful light bulb filaments were made of carbonCarbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
(from carbonized paper or bamboo
Bamboo
Bamboo is a group of perennial evergreens in the true grass family Poaceae, subfamily Bambusoideae, tribe Bambuseae. Giant bamboos are the largest members of the grass family....
). Early carbon filaments had a negative temperature coefficient of resistance -- as they got hotter, their electrical resistance decreased. This made the lamp sensitive to fluctuations in the power supply, since a small increase of voltage would cause the filament to heat up, reducing its resistance and causing it to draw even more power and heat even further. In the "flashing" process, carbon filaments were heated by current passing through them, while in an evacuated vessel containing hydrocarbon (gasoline) vapor. The carbon deposited by this treatment improved the uniformity and strength of filaments, and their efficiency. A metallized or graphitized filament was first heated in a high-temperature oven before flashing and lamp assembly; this transformed the carbon into graphite, which further strengthened and smoothed the filament, and as a byproduct had the advantage of changing the lamp to a positive temperature coefficient like a metallic conductor. This helped stabilize power consumption, temperature and light output against minor variations in supply voltage.
In 1902, the Siemens
Siemens
Siemens may refer toSiemens, a German family name carried by generations of telecommunications industrialists, including:* Werner von Siemens , inventor, founder of Siemens AG...
company developed a tantalum
Tantalum
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as tantalium, the name comes from Tantalus, a character in Greek mythology. Tantalum is a rare, hard, blue-gray, lustrous transition metal that is highly corrosion resistant. It is part of the refractory...
lamp filament. These lamps were more efficient than even graphitized carbon filaments and could operate at higher temperatures. Since the metal had a lower resistivity than carbon, the tantalum lamp filament was quite long and required multiple internal supports. The metal filament had the property of gradually shortening in use; the filaments were installed with large loops that tightened in use. This made lamps in use for several hundred hours quite fragile. Metal filaments had the property of breaking and re-welding, though this would usually decrease resistance and shorten the life of the filament. General Electric bought the rights to use tantalum filaments and produced them in the United States until 1913.
From 1898 to around 1905, osmium
Osmium
Osmium is a chemical element with the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-blacktransition metal in the platinum family, and is the densest natural element. Osmium is twice as dense as lead. The density of osmium is , slightly greater than that of iridium,...
was also used as a lamp filament in Europe, but the metal was so expensive that used broken lamps could be returned for part credit. It could not be made for 110 V or 220 V so several lamps were wired in series for use on standard voltage circuits.
In 1906, the tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
filament was introduced. Tungsten metal was initially not available in a form that allowed it to be drawn into fine wires. Filaments made from sintered tungsten powder were quite fragile. By 1910, a process was developed by William D. Coolidge at General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
for production of a ductile form of tungsten. The process required pressing chemically produced tungsten powder into bars, then several steps of sintering, swaging, and then wire drawing. It was found that very pure tungsten formed filaments that sagged in use, and that a very small "doping" treatment with potassium, silicon, and aluminum oxides at the level of a few hundred parts per million greatly improved the life and durability of the tungsten filaments.
To improve the efficiency of the lamp, the filament usually consists of coils of coiled fine wire, also known as a 'coiled coil.' For a 60-watt 120-volt lamp, the uncoiled length of the tungsten filament is usually 22.8 inches (57.9 cm), and the filament diameter is 0.0018 inch (0.004572 cm). The advantage of the coiled coil is that evaporation of the tungsten filament is at the rate of a tungsten cylinder having a diameter equal to that of the coiled coil. The coiled-coil filament evaporates more slowly than a straight filament of the same surface area and light-emitting power. If the filament is then run hotter to bring back evaporation to the same rate, the resulting filament is a more efficient light source.
There are several different shapes of filament used in lamps, with differing characteristics. Manufacturers designate the types with codes such as C-6, CC-6, C-2V, CC-2V, C-8, CC-88, C-2F, CC-2F, C-Bar, C-Bar-6, C-8I, C-2R, CC-2R, and Axial.
Hot cathode
In vacuum tubes, a hot cathode is a cathode electrode which emits electrons due to thermionic emission. In the accelerator community, these are referred to as thermionic cathodes. The heating element is usually an electrical filament...
s of 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 and vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
s as a source of electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s or in vacuum tubes to heat an electron-emitting electrode.
Reducing filament evaporation
One of the problems of the standard electric light bulb is evaporation of the filament. Small variations in resistivity along the filament cause "hot spots" to form at points of higher resistivity; a variation of diameter of only 1% will cause a 25% reduction in service life. The hot spots evaporate faster than the rest of the filament, increasing resistance at that point—a positive feedbackPositive feedback
Positive feedback is a process in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system that responds to a perturbation in a way that reduces its effect is...
that ends in the familiar tiny gap in an otherwise healthy-looking filament. Irving Langmuir
Irving Langmuir
Irving Langmuir was an American chemist and physicist. His most noted publication was the famous 1919 article "The Arrangement of Electrons in Atoms and Molecules" in which, building on Gilbert N. Lewis's cubical atom theory and Walther Kossel's chemical bonding theory, he outlined his...
found that an inert gas, instead of vacuum, would retard evaporation. General service incandescent light bulbs over about 25 watts in rating are now filled with a mixture of mostly 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 some nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, or sometimes krypton
Krypton
Krypton is a chemical element with the symbol Kr and atomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other...
. Xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
gas, much more expensive, is used occasionally in small bulbs, such as those for flashlights. Since a filament breaking in a gas-filled bulb can form an electric arc
Electric arc
An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on...
, which may spread between the terminals and draw very heavy current, intentionally thin lead-in wires or more elaborate protection devices are therefore often used as fuses
Fuse (electrical)
In electronics and electrical engineering, a fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit...
built into the light bulb.
More nitrogen is used in higher-voltage lamps to reduce the possibility of arcing.
While inert gas reduces filament evaporation, it also conducts heat from the filament, thereby cooling the filament and reducing efficiency. At constant pressure and temperature, the thermal conductivity of a gas depends upon the molecular weight of the gas and the cross sectional area of the gas molecules. Higher molecular weight gasses have lower thermal conductivity, because both the molecular weight is higher and also the cross sectional area is higher.
Xenon gas improves efficiency because of its high molecular weight,
but is also more expensive,
so its use is limited to smaller lamps.
During ordinary operation, the tungsten of the filament evaporates; hotter, more-efficient filaments evaporate faster. Because of this, the lifetime of a filament lamp is a trade-off between efficiency and longevity. The trade-off is typically set to provide a lifetime of several hundred to 2,000 hours for lamps used for general illumination. Theatrical, photographic, and projection lamps may have a useful life of only a few hours, trading life expectancy for high output in a compact form. Long-life general service lamps have lower efficiency but are used where the cost of changing the lamp is high compared to the value of energy used.
Filament notching describes another phenomenon that limits the life of lamps. Lamps operated on direct current develop random stair-step irregularities on the filament surface, reducing the cross section and further increasing heat and evaporation of tungsten at these points. In small lamps operated on direct current, lifespan may be cut in half compared to AC operation. Different alloys of tungsten and rhenium
Rhenium
Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-white, heavy, third-row transition metal in group 7 of the periodic table. With an average concentration of 1 part per billion , rhenium is one of the rarest elements in the Earth's crust. The free element has...
can be used to counteract the effect.
If a light bulb envelope leaks, the hot tungsten filament reacts with air, yielding an aerosol of brown tungsten nitride
Tungsten nitride
Tungsten nitride is an inorganic compound, a nitride of tungsten. It is a hard, solid, brown-colored ceramic material that is electrically conductive and decomposes in water....
, brown tungsten dioxide, violet-blue tungsten pentoxide
Tungsten pentoxide
Tungsten pentoxide was reported in early literature but proved to have the stoichiometry W18O49. Sometimes called mineral blue it is a blue solid formed by the reaction of tungsten trioxide, W2O3, and tungsten metal at 700 °C. There are a number of these unusual intermediate oxides formed from...
, and yellow tungsten trioxide
Tungsten trioxide
Tungsten oxide, also known as tungsten trioxide or tungstic anhydride, WO3, is a chemical compound containing oxygen and the transition metal tungsten. It is obtained as an intermediate in the recovery of tungsten from its minerals. Tungsten ores are treated with alkalis to produce WO3...
that then deposits on the nearby surfaces or the bulb interior.
Bulb blackening
In a conventional lamp, the evaporated tungsten eventually condenses on the inner surface of the glass envelope, darkening it. For bulbs that contain a vacuum, the darkening is uniform across the entire surface of the envelope. When a filling of inert gas is used, the evaporated tungsten is carried in the thermal convection currents of the gas, depositing preferentially on the uppermost part of the envelope and blackening just that portion of the envelope. An incandescent lamp that gives 93% or less of its initial light output at 75% of its rated life is regarded as unsatisfactory, when tested according to IEC Publication 60064. Light loss is due to filament evaporation and bulb blackening. Study of the problem of bulb blackening led to the discovery of the Edison effect, thermionic emissionThermionic emission
Thermionic emission is the heat-induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the binding potential, also known as work function of the metal. The charge carriers can be electrons or ions, and...
and invention of the vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
.
A very small amount of water vapor inside a light bulb can significantly affect lamp darkening. Water vapor dissociates into hydrogen and oxygen at the hot filament. The oxygen attacks the tungsten metal, and the resulting tungsten oxide particles travel to cooler parts of the lamp. Hydrogen from water vapor reduces the oxide, reforming water vapor and continuing this water cycle. The equivalent of a drop of water distributed over 500,000 lamps will significantly increase darkening. Small amounts of substances such as zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
are placed within the lamp as a getter
Getter
A getter is a deposit of reactive material that is deliberately placed inside a vacuum system, for the purpose of completing and maintaining the vacuum. When gas molecules strike the getter material, they combine with it chemically or by adsorption...
to react with any oxygen that may bake out of the lamp components during operation.
Some old, high-powered lamps used in theater, projection, searchlight, and lighthouse service with heavy, sturdy filaments contained loose tungsten powder within the envelope. From time to time, the operator would remove the bulb and shake it, allowing the tungsten powder to scrub off most of the tungsten that had condensed on the interior of the envelope, removing the blackening and brightening the lamp again.
Halogen lamps
Halogen lamp
A halogen lamp, also known as a tungsten halogen lamp, is an incandescent lamp with a tungsten filament contained within an inert gas and a small amount of a halogen such as iodine or bromine. The chemical halogen cycle redeposits evaporated tungsten back on to the filament, extending the life of...
reduces uneven evaporation of the filament and darkening of the envelope by filling the lamp with a halogen
Halogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...
gas at low pressure, rather than an inert gas. The halogen cycle increases the lifetime of the bulb and prevents its darkening by redepositing tungsten from the inside of the bulb back onto the filament. The halogen lamp can operate its filament at a higher temperature than a standard gas filled lamp of similar power without loss of operating life.
Incandescent arc lamps
A variation of the incandescent lamp did not use a hot wire filament, but instead used an arc struck on a spherical bead electrode to produce heat. The electrode then became incandescent, with the arc contributing little to the light produced. Such lamps were used for projection or illumination for scientific instruments such as microscopeMicroscope
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...
s. These arc lamps ran on relatively low voltages and incorporated tungsten filaments to start ionization within the envelope. They provided the intense concentrated light of an arc lamp
Arc lamp
"Arc lamp" or "arc light" is the general term for a class of lamps that produce light by an electric arc . The lamp consists of two electrodes, first made from carbon but typically made today of tungsten, which are separated by a gas...
but were easier to operate. Developed around 1915, these lamps were displaced by mercury and xenon arc lamp
Xenon arc lamp
A xenon arc lamp is a specialized type of gas discharge lamp, an electric light that produces light by passing electricity through ionized xenon gas at high pressure to produce a bright white light that closely mimics natural sunlight...
s.
Power
Incandescent lamps are nearly pure resistive loads with a power factorPower factor
The power factor of an AC electric power system is defined as the ratio of the real power flowing to the load over the apparent power in the circuit, and is a dimensionless number between 0 and 1 . Real power is the capacity of the circuit for performing work in a particular time...
of 1. This means the actual power consumed (in watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s) and the apparent power (in volt-ampere
Volt-ampere
A volt-ampere is the unit used for the apparent power in an electrical circuit, equal to the product of root-mean-square voltage and RMS current. In direct current circuits, this product is equal to the real power in watts...
s) are equal. Incandescent light bulbs are usually marketed
Marketing
Marketing is the process used to determine what products or services may be of interest to customers, and the strategy to use in sales, communications and business development. It generates the strategy that underlies sales techniques, business communication, and business developments...
according to the electrical power
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...
consumed. This is measured in watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s and depends mainly on the resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
of the filament, which in turn depends mainly on the filament's length, thickness, and material. For two bulbs of the same voltage, type, color, and clarity, the higher-powered bulb gives more light.
The table shows the approximate typical output, in lumens
Lumen (unit)
The lumen is the SI derived unit of luminous flux, a measure of the total "amount" of visible light emitted by a source. Luminous flux differs from power in that luminous flux measurements reflect the varying sensitivity of the human eye to different wavelengths of light, while radiant flux...
, of standard incandescent light bulbs at various powers. Note that the lumen values for "soft white" bulbs will generally be slightly lower than for standard bulbs at the same power, while clear bulbs will usually emit a slightly brighter light than correspondingly powered standard bulbs.
Current and resistance
The actual resistance of the filament is temperature-dependent. The cold resistance of tungsten-filament lamps is about 1/15 the hot-filament resistance when the lamp is operating. For example, a 100-watt, 120-volt lamp has a resistance of 144 ohmOhm
The ohm is the SI unit of electrical resistance, named after German physicist Georg Simon Ohm.- Definition :The ohm is defined as a resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere,...
s when lit, but the cold resistance is much lower (about 9.5 ohms). Since incandescent lamps are resistive loads, simple phase-control triac
Thyristor
A thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as bistable switches, conducting when their gate receives a current trigger, and continue to conduct while they are forward biased .Some sources define silicon controlled rectifiers and...
dimmers can be used to control brightness. Electrical contacts may carry a "T" rating symbol indicating that they are designed to control circuits with the high inrush current characteristic of tungsten lamps. For a 100-watt, 120-volt general-service lamp, the current stabilizes in about 0.10 seconds, and the lamp reaches 90% of its full brightness after about 0.13 seconds.
| Power (W Watt The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:... ) |
Output (lm Lumen (unit) The lumen is the SI derived unit of luminous flux, a measure of the total "amount" of visible light emitted by a source. Luminous flux differs from power in that luminous flux measurements reflect the varying sensitivity of the human eye to different wavelengths of light, while radiant flux... ) |
Efficacy (lm/W) |
|---|---|---|
| 5 | 25 | 5 |
| 15 | 110 | 7.3 |
| 25 | 200 | 8.0 |
| 35 | 350 | 10.0 |
| 40 | 500 | 12.5 |
| 50 | 700 | 14.0 |
| 55 | 800 | 14.5 |
| 60 | 850 | 14.2 |
| 65 | 1,000 | 15.4 |
| 70 | 1,100 | 15.7 |
| 75 | 1,200 | 16.0 |
| 90 | 1,450 | 16.1 |
| 95 | 1,600 | 16.8 |
| 100 | 1,700 | 17.0 |
| 135 | 2,350 | 17.4 |
| 150 | 2,850 | 19.0 |
| 200 | 3,900 | 19.5 |
| 300 | 6,200 | 20.7 |
Bulb shapes
Incandescent light bulbs come in a range of shapes and sizes. The names of the shapes may be slightly different in some regions. Many of these shapes have a designation consisting of one or more letters followed by one or more numbers, e.g. A55 or PAR38. The letters represent the shape of the bulb. The numbers represent the maximum diameter, either in of an inch, or in millimetres, depending on the shape and the region. For example, 63 mm reflectors are designated R63, but in the U.S. they are known as R20 (2.5 in). However, in both regions, a PAR38 reflector is known as PAR38. In Australia an R80 is 1 in in diameter.Common shapes:
General Service
- Light emitted in (nearly) all directions. Available either clear or frosted.
- Types: General (A), Mushroom
High Wattage General Service
- Lamps greater than 200 watts.
- Types: Pear-shaped (PS)
Decorative
- lamps used in chandeliers, etc.
- Types: candle (B), twisted candle, bent-tip candle (CA & BA), flame (F), fancy round (P), globe (G)
Reflector (R): Reflective coating inside the bulb directs light forward. Flood types (FL) spread light. Spot types (SP) concentrate the light. Reflector (R) bulbs put approximately double the amount of light (foot-candles) on the front central area as General Service (A) of same wattage.
- Types: Standard reflector (R), elliptical reflector (ER), crown-silvered
Parabolic aluminized reflector (PAR)
- Parabolic aluminized reflectorParabolic aluminized reflector lightA parabolic aluminized reflector lamp is a type of electric lamp that is widely used in commercial, residential, and transportation illumination. Usage includes locomotive headlamps, aircraft landing lights, and residential and commercial recessed lights...
(PAR) bulbs control light more precisely. They produce about four times the concentrated light intensity of general service (A), and are used in recessed and track lighting. Weatherproof casings are available for outdoor spot and flood fixtures. - 120 V sizes: PAR 16, 20, 30, 38, 56 and 64
- 230 V sizes: Par 38, 56 and 64
- Available in numerous spot and flood beam spreads. Like all light bulbs, the number represents the diameter of the bulb in of an inch. Therefore, a PAR 16 is 2 in in diameter, a PAR 20 is 2.5 in in diameter, PAR 30 is 3.75 in and a PAR 38 is 4.75 in in diameter.
Multifaceted reflector (MR)
HIR: "HIR" is a GE
Gê
Gê are the people who spoke Ge languages of the northern South American Caribbean coast and Brazil. In Brazil the Gê were found in Rio de Janeiro, Minas Gerais, Bahia, Piaui, Mato Grosso, Goias, Tocantins, Maranhão, and as far south as Paraguay....
designation for a lamp with an infrared reflective coating. Since less heat escapes, the filament burns hotter and more efficiently. The Osram
Osram
Osram, founded 1919, is part of the industry sector of Siemens AG and one of the two leading lighting manufacturers in the world. The name is derived from osmium and Wolfram , as both these elements were commonly used for lighting filaments at the time the company was founded...
designation for a similar coating is "IRC".
Lamp bases
Very small lamps may have the filament support wires extended through the base of the lamp, and can be directly soldered to a printed circuit board for connections. Some reflector-type lamps include screw terminals for connection of wires. Most lamps have metal bases that fit in a socket to support the lamp and conduct current to the filament wires. In the late 19th century, manufacturers introduced a multitude of incompatible lamp bases. General ElectricGeneral Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
introduced standard base sizes for tungsten incandescent lamps under the Mazda
Mazda (light bulb)
Mazda was a trademarked name created by the Shelby Electric Company for incandescent light bulbs. The name was used from 1909 through 1945 in the United States by Shelby and later General Electric; Mazda brand light bulbs were made for decades after 1945 outside the USA...
trademark in 1909. This standard was soon adopted across the United States, and the Mazda name was used by many manufacturers under license through 1945. Today most incandescent lamps for general lighting service use an Edison screw
Edison screw
The Edison screw fitting is a system of connectors used for light bulbs, developed by Thomas Edison and licensed starting in 1909 under the Mazda trademark. Most have a right-hand threading, so that it goes in when turned clockwise and comes out when turned counterclockwise, like a hardware screw...
in candelabra, intermediate, or standard or mogul sizes, or double contact bayonet
Bayonet mount
A bayonet mount or bayonet connector is a fastening mechanism consisting of a male side with one or more pins, and a female receptor with matching L slots and spring to keep the two parts locked together....
base. Bayonet base lamps are frequently used in automotive lamps
Automotive lamp types
A modern vehicle uses different kinds of lamps for multiple purposes: illumination for the driver to be able to drive in dark conditions, illumination to be seen and lights for information displays. Types of these lamps vary depending on the purpose and different car manufacturers and models use...
to resist loosening due to vibration. A bipin
Bipin
A bipin or bi-pin, , is a standard from the IEC for lamp fittings. These are used on many small incandescent light bulbs , and on most fluorescent lights as well, where the filaments are involved in starting the tube when it is turned on.Some lamps have pins placed closer together, preventing...
base is often used for halogen or reflector lamps.
Lamp bases may be secured to the bulb with a cement, or by mechanical crimping to indentations molded into the glass bulb.
Wedge base
A wedge base is a type of electrical connector used as a fitting for small light bulbs. It is similar to the bi-pin connector, except that the two "pins" are the same wires that extend into the bulb , and the wires are bent up onto the sides of the base, where they make contact with the socket...
s that have a partial plastic or even completely glass base. In this case, the wires wrap around to the outside of the bulb, where they press against the contacts in the socket. Miniature Christmas bulbs use a plastic wedge base as well.
Lamps intended for use in optical systems (such as film projectors, microscope illuminators, or stage lighting instruments have bases with alignment features so that the filament is positioned accurately within the optical system. A screw-base lamp may have a random orientation of the filament when the lamp is installed in the socket.
Light output and lifetime
Incandescent lamps are very sensitive to changes in the supply voltage. These characteristics are of great practical and economic importance.For a supply voltage V near the rated voltage of the lamp:
- Light output is approximately proportional to V 3.4
- Power consumption is approximately proportional to V 1.6
- Lifetime is approximately proportional to V −16
- Color temperature is approximately proportional to V 0.42
This means that a 5% reduction in operating voltage will more than double the life of the bulb, at the expense of reducing its light output by about 20%. This may be a very acceptable trade off for a light bulb that is in a difficult-to-access location (for example, traffic lights or fixtures hung from high ceilings). Long-life bulbs take advantage of this trade-off. Since the value of the electric power they consume is much more than the value of the lamp, general service lamps emphasize efficiency over long operating life. The objective is to minimize the cost of light, not the cost of lamps.
The relationships above are valid for only a few percent change of voltage around rated conditions, but they do indicate that a lamp operated at much lower than rated voltage could last for hundreds of times longer than at rated conditions, albeit with greatly reduced light output. The Centennial Light
Centennial Light
The Centennial Light is the world's longest-lasting light bulb. It is at 4550 East Avenue, Livermore, California, and maintained by the Livermore-Pleasanton Fire Department. The fire department says that the bulb is at least 110 years old and has been turned off only a handful of times...
is a light bulb that is accepted by the Guinness Book of World Records as having been burning almost continuously at a fire station
Fire station
A fire station is a structure or other area set aside for storage of firefighting apparatus , personal protective equipment, fire hose, fire extinguishers, and other fire extinguishing equipment...
in Livermore, California
Livermore, California
Livermore is a city in Alameda County. The population as of 2010 was 80,968. Livermore is located on the eastern edge of California's San Francisco Bay Area....
, since 1901. However, the bulb is powered by only four watts. A similar story can be told of a 40-watt bulb in Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
that has been illuminated since September 21, 1908. It once resided in an opera house
Opera house
An opera house is a theatre building used for opera performances that consists of a stage, an orchestra pit, audience seating, and backstage facilities for costumes and set building...
where notable celebrities stopped to take in its glow, but is now in an area museum
Museum
A museum is an institution that cares for a collection of artifacts and other objects of scientific, artistic, cultural, or historical importance and makes them available for public viewing through exhibits that may be permanent or temporary. Most large museums are located in major cities...
.
In flood lamps used for photographic
Photography
Photography 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...
lighting, the tradeoff is made in the other direction. Compared to general-service bulbs, for the same power, these bulbs produce far more light, and (more importantly) light at a higher color temperature, at the expense of greatly reduced life (which may be as short as two hours for a type P1 lamp). The upper temperature limit for the filament is the melting point of the metal. Tungsten is the metal with the highest melting point, 3695 kelvins (6,191.3 °F). A 50-hour-life projection bulb, for instance, is designed to operate only 50 °C (122 °F) below that melting point. Such a lamp may achieve up to 22 lumens per watt, compared with 17.5 for a 750-hour general service lamp.
Lamps designed for different voltages have different luminous efficacy. For example, a 100-watt, 120-volt lamp will produce about 17.1 lumens per watt. A lamp with the same rated lifetime but designed for 230 V would produce only around 12.8 lumens per watt, and a similar lamp designed for 30 volts (train lighting) would produce as much as 19.8 lumens per watt. Lower voltage lamps have a thicker filament, for the same power rating. They can run hotter for the same lifetime before the filament evaporates.
The wires used to support the filament make it mechanically stronger, but remove heat, creating another tradeoff between efficiency and long life. Many general-service 120-volt lamps use no additional support wires, but lamps designed for "rough service" or "vibration service" may have as many as five. Low-voltage lamps have filaments made of heavier wire and do not require additional support wires.
Very low voltages are inefficient since the lead wires would conduct too much heat away from the filament, so the practical lower limit for incandescent lamps is 1.5 volts. Very long filaments for high voltages are fragile, and lamp bases become more difficult to insulate, so lamps for illumination are not made with rated voltages over 300 volts. Some infrared heating elements are made for higher voltages, but these use tubular bulbs with widely separated terminals.
Health issues
Although some sources claim fluorescent lighting causes more health problems than incandescent lighting (see Light sensitivityLight sensitivity
Light sensitivity or photosensitivity is an increase in the reactivity of the skin to sunlight. Apart from vision, human beings have many physiological and psychological responses to light. In rare individuals an atypical response may result in serious discomfort, disease, or injury. Some drugs...
and Over-illumination for discussion), more research needs to be done in this field. According to the European Commission Scientific Committee on Emerging and Newly Identified Health Risks
Scientific Committee on Emerging and Newly Identified Health Risks
The Scientific Committee on Emerging and Newly Identified Health Risks is one of the independent scientific committees managed by the Directorate-General for Health and Consumer Protection of the European Commission, which provide scientific advice to the Commission on issues related to consumer...
(SCENIHR) in 2008, the only property of compact fluorescent lamps that could pose an added health risk is the ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
and blue light emitted by such devices. The worst that can happen is that this radiation could aggravate symptoms in people who already suffer rare skin conditions that make them exceptionally sensitive to light. They also stated that more research is needed to establish whether compact fluorescent lamps constitute any higher risk than incandescent lamps.
Radio interference
Incandescent bulbs do not produce significant radio frequency interference, a concern with many other light sources, such as most LED and fluorescent lamps.External links
- Museum of Electric Lamp Technology
- Howstuffworks - "How Light Bulbs Work"
- Light Source Spectra 60 W-100 W Incandescent light bulb spectra
- Halogen Light Bulbs – Base Identification
- Light Bulbs - Lamps and Tubes - Lamp Bases Explained
- The Perfection of the Electric Light Bulb – background and experiment
- Incandescent Light Bulb's Bulb and Base Types Explained
- Examples of how color temperature of light bulbs affect our surroundings
- An brief article explaing the light bulb - "The Composition of the Light Bulb"
- The history of the light bulb
- BanTheBulb.Org energy efficiency campaign
- Great light bulbs gallery