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An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire
filament The word filament, which is descended from Latin ''filum'' meaning " thread", is used in English for a variety of thread-like structures, including: Astronomy * Galaxy filament, the largest known cosmic structures in the universe * Solar filament ...
heated until it glows. The filament is enclosed in a glass bulb with a vacuum or inert gas to protect the filament from oxidation. Current is supplied to the filament by terminals or wires embedded in the glass. A bulb socket provides mechanical support and electrical connections. Incandescent bulbs are manufactured in a wide range of sizes, light output, and voltage ratings, from 1.5 volts to about 300 volts. They require no external regulating equipment, have low
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. It is a factor in ...
s, and work equally well on either
alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in which ...
or direct current. As a result, the incandescent bulb became widely used in household and commercial lighting, for portable lighting such as table lamps, car headlamps, and
flashlight A flashlight ( US, Canada) or torch ( UK, Australia) is a portable hand-held electric lamp. Formerly, the light source typically was a miniature incandescent light bulb, but these have been displaced by light-emitting diodes (LEDs) since the ...
s, and for decorative and advertising lighting. Incandescent bulbs are much less efficient than other types of electric lighting, converting less than 5% of the energy into visible light. The remaining energy is lost as heat. The luminous efficacy of a typical incandescent bulb for 120 V operation is 16 lumens per watt, compared with 60 lm/W for a
compact fluorescent A compact fluorescent lamp (CFL), also called compact fluorescent light, energy-saving light and compact fluorescent tube, is a fluorescent lamp designed to replace an incandescent light bulb; some types fit into light fixtures designed for inca ...
bulb or 150 lm/W for some white
LED lamp An LED lamp or LED light bulb is an electric light that produces light using light-emitting diodes (LEDs). LED lamps are significantly more energy-efficient than equivalent incandescent lamps and can be significantly more efficient than mo ...
s. The heat produced by filaments is used in some applications, such as heat lamps in
incubator An incubator is anything that performs or facilitates various forms of incubation, and may refer to: Biology and medicine * Incubator (culture), a device used to grow and maintain microbiological cultures or cell cultures * Incubator (egg), a de ...
s,
lava lamp A lava lamp is a decorative lamp, invented in 1963 by British entrepreneur Edward Craven Walker, the founder of the lighting company Mathmos. It consists of a bolus of a special coloured wax mixture inside a glass vessel, the remainder of whi ...
s, and the Easy-Bake Oven toy. Quartz envelope halogen
infrared heater An infrared heater or heat lamp 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 peak of the i ...
s are used for industrial processes such as paint curing and space heating. Incandescent bulbs typically have short lifetimes compared with other types of lighting; around 1,000 hours for home light bulbs versus typically 10,000 hours for compact fluorescents and 20,000–30,000 hours for lighting LEDs. Most incandescent bulbs can be replaced by
fluorescent lamp A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet lig ...
s, high-intensity discharge lamps, and light-emitting diode lamps (LED). Some administrations have begun a
phase-out of incandescent light bulbs Various governments have passed regulations to phase out manufacturing or importation of incandescent light bulbs for general lighting in favor of more energy- efficient alternatives. The regulations are generally based on efficiency, rather ...
to reduce energy consumption.


History

Historians Robert Friedel and Paul Israel list inventors of incandescent lamps prior to
Joseph Swan Sir Joseph Wilson Swan FRS (31 October 1828 – 27 May 1914) was an English physicist, chemist, and inventor. He is known as an independent early developer of a successful incandescent light bulb, and is the person responsible for develop ...
and Thomas Edison. They conclude that Edison's version was able to outstrip the others because of a combination of three factors: an effective
incandescent Incandescence is the emission of electromagnetic radiation (including visible light) from a hot body as a result of its high temperature. The term derives from the Latin verb ''incandescere,'' to glow white. A common use of incandescence i ...
material, a higher vacuum than others were able to achieve (by use of the Sprengel pump) and a high resistance that made power distribution from a centralized source economically viable. Historian Thomas Hughes has attributed Edison's success to his development of an entire, integrated system of electric lighting.


Early pre-commercial research

In 1761,
Ebenezer Kinnersley Ebenezer Kinnersley (30 November 1711 – 4 July 1778]) was an English scientist, inventor and lecturer, specializing in the investigation of electricity. Life and Scientific Studies Ebenezer Kinnersley was a son of Rev. William Kinnersley, a ...
demonstrated heating a wire to incandescence. In 1802,
Humphry Davy Sir Humphry Davy, 1st Baronet, (17 December 177829 May 1829) was a British chemist and inventor who invented the Davy lamp and a very early form of arc lamp. He is also remembered for isolating, by using electricity, several elements for the ...
used what he described as "a battery of immense size", consisting of 2,000 cells housed in the basement of the Royal Institution of Great Britain, to create an incandescent light by passing the current through a thin strip of
platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Platin ...
, chosen because the metal had an extremely high melting point. 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.Davis, L.J. "Fleet Fire." Arcade Publishing, New York, 2003. 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 (8 September 1799 – 29 June 1862) was a Scottish inventor and author. He is credited with early developments in several fields, such as incandescent lighting and telegraphy. Life and work James Bowman Lindsay was bo ...
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 he did not develop the electric light any further. In 1838, Belgian lithographer
Marcellin Jobard Jean-Baptiste-Ambroise-Marcellin Jobard (17 May 1792 – 27 October 1861) was a Belgian lithographer, photographer and inventor of French origin. Founder of the first significant Belgian lithographic establishment, first photographer in Belgium ...
invented an incandescent light bulb with a vacuum atmosphere using a carbon filament. In 1840, British scientist Warren De la Rue enclosed a coiled platinum filament in a vacuum tube and passed an electric current through it. The design was based on the concept that the high melting point 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 a workable design, the cost of the platinum made it impractical for commercial use. In 1841, Frederick de Moleyns of England was granted the first patent for an incandescent lamp, with a design using platinum wires contained within a vacuum bulb. He also used carbon. In 1845, American John W. Starr patented an incandescent light bulb using carbon filaments. His invention was never produced commercially. In 1851,
Jean Eugène Robert-Houdin Jean may refer to: People * Jean (female given name) * Jean (male given name) * Jean (surname) Fictional characters * Jean Grey, a Marvel Comics character * Jean Valjean, fictional character in novel ''Les Misérables'' and its adaptations * Je ...
publicly demonstrated incandescent light bulbs on his estate in Blois, France. His light bulbs are on display in the museum of the
Château de Blois A château (; plural: châteaux) is a manor house or residence of the lord of the manor, or a fine country house of nobility or gentry, with or without fortifications, originally, and still most frequently, in French-speaking regions. Nowaday ...
. In 1859,
Moses G. Farmer Moses Gerrish Farmer (February 9, 1820 – May 25, 1893) was an electrical engineer and inventor. Farmer was a member to the AIEE, later known as the IEEE. Biography Farmer was born at Boscawen, New Hampshire. He received his schooling at Phill ...
built an electric incandescent light bulb using a platinum filament. Thomas Edison later saw one of these bulbs in a shop in Boston, and asked Farmer for advice on the electric light business. In 1872, Russian
Alexander Lodygin Alexander Nikolayevich Lodygin, known after immigration to US as Alexandre de Lodyguine (russian: Александр Николаевич Лодыгин; 18 October 1847 – 16 March 1923) was a Russian electrical engineer and inventor, one of ...
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 US, changed his name to Alexander de Lodyguine and applied for and obtained patents for incandescent lamps having
chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...
, iridium, rhodium,
ruthenium Ruthenium is a chemical element with the 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 other chemicals ...
, osmium, molybdenum and tungsten filaments, and a bulb using a molybdenum filament was demonstrated at the
world fair A world's fair, also known as a universal exhibition or an expo, is a large international exhibition designed to showcase the achievements of nations. These exhibitions vary in character and are held in different parts of the world at a specif ...
of 1900 in Paris. On 24 July 1874, a Canadian patent was filed by Henry Woodward and
Mathew Evans Matthew 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. patent on the device. Evans, from Toronto, Ontario Ontario ( ; ) is one of the thirte ...
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. (Edison needed ownership of the novel claim of lamps connected in a parallel circuit). On 4 March 1880, just five months after Edison's light bulb,
Alessandro Cruto Alessandro Cruto was an Italian inventor, born in the town of Piossasco, near Turin, who created an early incandescent light bulb. Son of a construction foreman, he attended the school of architecture at the University of Turin, while also atte ...
created his first incandescent lamp. Cruto produced a filament by deposition of graphite on thin platinum filaments, by heating it with an electric current in the presence of gaseous ethyl alcohol. Heating this platinum at high temperatures leaves behind thin filaments of platinum coated with pure graphite. By September 1881 he had achieved a successful version of this the first synthetic filament. The light bulb invented by Cruto lasted five hundred hours as opposed to the forty of Edison's original version. In 1882 Munich Electrical Exhibition in Bavaria, Germany Cruto's lamp was more efficient than the Edison's one and produced a better, white light. In 1893,
Heinrich Göbel Heinrich Göbel, or Henry Goebel (April 20, 1818 – December 4, 1893) was a German-born American precision mechanic and inventor. In 1848 he emigrated to New York City, where he resided until his death. He received American citizenship in 1865. ...
claimed he had designed the first incandescent light bulb in 1854, with a thin carbonized
bamboo Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, but ...
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 Göbel
anticipation Anticipation is an emotion involving pleasure or anxiety in considering or awaiting an expected event. Anticipatory emotions include fear, anxiety, hope and trust. When the anticipated event fails to occur, it results in disappointment (if posi ...
, but there was never a decision in a final hearing due to the expiration of Edison's patent. A research work published 2007 concluded that the story of the Göbel lamps in the 1850s is fictitious.


Commercialization


Carbon filament and vacuum

Joseph Swan Sir Joseph Wilson Swan FRS (31 October 1828 – 27 May 1914) was an English physicist, chemist, and inventor. He is known as an independent early developer of a successful incandescent light bulb, and is the person responsible for develop ...
(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 had become 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 a British Patent 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. This bulb lasted about 40 hours. Swan then 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' in the early 1880s and obtained British Patent 4933 that same year. From this year he began installing light bulbs in homes and landmarks in England. His house, Underhill, Low Fell, Gateshead, was the first in the world to be lit by a lightbulb. In the early 1880s he had started his company. In 1881, the
Savoy Theatre The Savoy Theatre is a West End theatre in the Strand in the City of Westminster, London, England. The theatre was designed by C. J. Phipps for Richard D'Oyly Carte and opened on 10 October 1881 on a site previously occupied by the Savoy P ...
in the
City of Westminster The City of Westminster is a city and borough in Inner London. It is the site of the United Kingdom's Houses of Parliament and much of the British government. It occupies a large area of central Greater London, including most of the West En ...
, 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."The Savoy Theatre", '' The Times'', 3 October 1881 The first street in the world to be lit by an incandescent lightbulb was Mosley Street,
Newcastle upon Tyne Newcastle upon Tyne (Received Pronunciation, RP: , ), or simply Newcastle, is a City status in the United Kingdom, city and metropolitan borough in Tyne and Wear, England. The city is located on the River Tyne's northern bank and forms the la ...
, United Kingdom. It was lit by Joseph Swan's incandescent lamp on 3 February 1879. Thomas Edison began serious research into developing a practical incandescent lamp in 1878. Edison filed his first patent application for "Improvement in Electric Lights" on 14 October 1878. After many experiments, first with carbon in the early 1880s and then with
platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Platin ...
and other metals, in the end Edison returned to a carbon filament. The first successful test was on 22 October 1879, and lasted 13.5 hours. Edison continued to improve this design and by 4 November 1879, filed for a US patent for an electric lamp using "a carbon filament or strip coiled and connected ... to platina contact wires." granted 27 January 1880 Although the patent described several ways of creating the carbon filament including using "cotton and linen thread, wood splints, papers coiled in various ways," Edison and his team later discovered that a carbonized bamboo filament could last more than 1200 hours. In 1880, the Oregon Railroad and Navigation Company steamer, ''Columbia'', became the first application for Edison's incandescent electric lamps (it was also the first ship to use a
dynamo "Dynamo Electric Machine" (end view, partly section, ) A dynamo is an electrical generator that creates direct current using a commutator. Dynamos were the first electrical generators capable of delivering power for industry, and the foundat ...
).
Albon Man Albon Man (June 29, 1826 – February 18, 1905) was an American lawyer, scientist, and inventor who was associated with the early technology of the incandescent light bulb. He worked with William Edward Sawyer to develop inventions. He was a sc ...
, a New York lawyer, started Electro-Dynamic Light Company in 1878 to exploit his patents and those of William Sawyer. Weeks later the United States Electric Lighting Company was organized. This company didn't make their first commercial installation of incandescent lamps until the fall of 1880 at the Mercantile Safe Deposit Company in New York City, about six months after the Edison incandescent lamps had been installed on the ''Columbia''.
Hiram S. Maxim Sir Hiram Stevens Maxim (5 February 1840 – 24 November 1916) was an American-British inventor best known as the creator of the first automatic machine gun, the Maxim gun. Maxim held patents on numerous mechanical devices such as hair-cur ...
was the chief engineer at the United States Electric Lighting Company. After the great success in the United States, the incandescent light bulb patented by Edison also began to gain widespread popularity in Europe as well; among other places, the first Edison light bulbs in the Nordic countries were installed at the weaving hall of the Finlayson's textile factory in
Tampere, Finland Tampere ( , , ; sv, Tammerfors, ) is a city in the Pirkanmaa region, located in the western part of Finland. Tampere is the most populous inland city in the Nordic countries. It has a population of 244,029; the urban area has a population o ...
in March 1882.
Lewis Latimer Lewis Howard Latimer (September 4, 1848 – December 11, 1928) was an African-American inventor and patent draftsman. His inventions included an evaporative air conditioner, an improved process for manufacturing carbon filaments for light bulbs, ...
, employed at the time by Edison, developed an improved method of heat-treating carbon filaments which reduced breakage and allowed them to be molded into novel shapes, such as the characteristic "M" shape of Maxim filaments. On 17 January 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.Fouché, Rayvon, ''Black Inventors in the Age of Segregation: Granville T. Woods, Lewis H. Latimer, and Shelby J. Davidson.'') (Johns Hopkins University Press, Baltimore & London, 2003, pp. 115–116. In Britain, the Edison and Swan companies merged into the Edison and Swan United Electric Company (later known as Ediswan, and ultimately incorporated into Thorn Lighting Ltd). Edison was initially against this combination, but after Swan
sued - A lawsuit is a proceeding by a party or parties against another in the civil court of law. The archaic term "suit in law" is found in only a small number of laws still in effect today. The term "lawsuit" is used in reference to a civil acti ...
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 US patent rights to the
Brush Electric Company Brush Electrical Machines is a manufacturer of electrical generators typically for gas turbine and steam turbine driven applications. The main office is based at Loughborough in Leicestershire, UK. History Charles Francis Brush, born in Euclid ...
in June 1882. The
United States Patent Office The United States Patent and Trademark Office (USPTO) is an agency in the U.S. Department of Commerce that serves as the national patent office and trademark registration authority for the United States. The USPTO's headquarters are in Alex ...
gave a ruling 8 October 1883, that Edison's patents were based on the prior art of William Sawyer and were invalid. Litigation continued for a number of years. Eventually on 6 October 1889, a judge ruled that Edison's electric light improvement claim for "a filament of carbon of high resistance" was valid. The main difficulty with vacuumizing the lamps was moisture adsorbing to the glass inside the bulb, which, if not removed,
split Split(s) or The Split may refer to: Places * Split, Croatia, the largest coastal city in Croatia * Split Island, Canada, an island in the Hudson Bay * Split Island, Falkland Islands * Split Island, Fiji, better known as Hạfliua Arts, enterta ...
when the lamp was lit, with resulting oxygen attacking the filament. In the 1880s,
phosphoric anhydride Phosphorus pentoxide is a chemical compound with molecular formula P4 O10 (with its common name derived from its empirical formula, P2O5). This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant and dehydra ...
was used in combination with expensive mercury vacuum pumps. However, about 1893, Italian inventor (1865–1939), who lacked these pumps, discovered that introduction of phosphorus vapours did the job of chemically bounding the remaining amounts of water and oxygen. In 1896 he patented a process of introducing red phosphorus as the so-called getter (a much later term) inside the bulb (now mostly replaced by triphosphorus pentanitride), which allowed obtaining economic bulbs lasting 800 hours; his patent was acquired by Edison in 1898. In 1897, German physicist and chemist Walther Nernst developed the
Nernst lamp The Nernst lamp was an early form of incandescent lamp. Construction Nernst lamps did not use a glowing tungsten filament. Instead, they used a ceramic rod that was heated to incandescence. Because the rod (unlike tungsten wire) would not ...
, a form of incandescent lamp that used a ceramic
globar A Globar is used as thermal light source for infrared spectroscopy. The preffered material for making Globar is silicon carbide that is shaped as rods or arches of various sizes. When inserted into a circuit that provides it with electric current, ...
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.


Metal filament, inert gas

US575002A patent on 01.Dec.1897 to Alexander Lodyguine (Lodygin, Russia) describes filament made of rare metals, amongst them was tungsten. Lodygin invented a process where rare metals such as tungsten can be chemically treated and heat-vaporized onto an electrically heated thread-like wire (platinum, carbon, gold) acting as a temporary base or skeletal form. (US patent 575,002). Lodygin later sold the patent rights to GE. In 1902, Siemens developed a tantalum lamp filament that was more efficient than even graphitized carbon filaments since they could operate at higher temperature. Since tantalum metal has a lower resistivity than carbon, the tantalum lamp filament was quite long and required multiple internal supports. The metal filament gradually shortened in use; the filaments were installed with large slack loops. Lamps used for several hundred hours became 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 US until 1913. From 1898 to around 1905, osmium was also used as a lamp filament in Europe. The metal was so expensive that used broken lamps could be returned for partial 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.


Tungsten filament

On 13 December 1904, Hungarian Sándor Just and Croatian
Franjo Hanaman Franjo Hanaman (June 30, 1878 – January 23, 1941) was a Croatian inventor, engineer, and chemist, who gained world recognition for inventing the world's first applied electric light-bulb with a metal filament (tungsten) with his assistant Alex ...
were granted a Hungarian patent (No. 34541) for a tungsten filament lamp that lasted longer and gave brighter light than the carbon filament. Tungsten filament lamps were first marketed by the Hungarian company
Tungsram Tungsram was a manufacturing company located in Hungary and known for their light bulbs and electronics. Established in Újpest (today part of Budapest, Hungary) in 1896, it initially produced telephones, wires and switchboards. The name "Tungsra ...
in 1904. This type is often called Tungsram-bulbs in many European countries. Filling a bulb with an inert gas such as
argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
or nitrogen slows down the evaporation of the tungsten filament compared to operating it in a vacuum. This allows for greater temperatures and therefore greater efficacy with less reduction in filament life. In 1906, William D. Coolidge developed a method of making "ductile tungsten" from
sintered Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing ...
tungsten which could be made into filaments while working for
General Electric Company The General Electric Company (GEC) was a major British industrial conglomerate involved in consumer and defence electronics, communications, and engineering. The company was founded in 1886, was Britain's largest private employer with over 250 ...
. By 1911 General Electric had begun selling incandescent light bulbs with ductile tungsten wire. In 1913, Irving Langmuir found that filling a lamp with inert gas instead of a vacuum resulted in twice the luminous efficacy and reduced bulb blackening. In 1917, Burnie Lee Benbow was granted a patent for the ''coiled coil filament'', in which a coiled filament is then itself wrapped into a coil by use of a mandrel. In 1921, Junichi Miura created the first double-coil bulb using a coiled coil tungsten filament while working for Hakunetsusha (a predecessor of Toshiba). At the time, machinery to mass-produce coiled coil filaments did not exist. Hakunetsusha developed a method to mass-produce coiled coil filaments by 1936. Between 1924 and the outbreak of the Second World War, the
Phoebus cartel The Phoebus cartel was an oligopoly that controlled the manufacture and sale of incandescent light bulbs. They appropriated market territories and lowered the useful life of such bulbs. Corporations based in Europe and the United States founded t ...
attempted to fix prices and sales quotas for bulb manufacturers outside of North America. In 1925,
Marvin Pipkin Marvin Pipkin (November 18, 1889 – January 7, 1977) was an American chemist, engineer, and scientist. During his time in the United States Army, he worked on gas mask innovations. These masks were used by soldiers as well as the public during ...
, an American chemist, patented a process for
frost Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above- freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor (a ga ...
ing the inside of lamp bulbs without weakening them. In 1947, he patented a process for coating the inside of lamps with silica. In 1930, Hungarian
Imre Bródy Imre Bródy (1891, Gyula, HungaryAntal Papp: Magyarország (Hungary), Panoráma, Budapest, 1982, , p. 860, pp. 453-456–1944, Mühldorf) was a Hungarian physicist who invented in 1930 the krypton-filled fluorescent lamps (also known as the k ...
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 () 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 second century CE, the territory was conquered by the Romans. The Hungarians occu ...
in 1937, in a factory co-designed by Polányi and Hungarian-born physicist
Egon Orowan Egon Orowan FRS ( hu, Orován Egon) (August 2, 1902 – August 3, 1989) was a Hungarian-British physicist and metallurgist. According to György Marx, he was one of The Martians. Life Orowan was born in the Óbuda district of Budapest. H ...
. 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.''Incandescent Lamps, Publication Number TP-110'', General Electric Company, Nela Park, Cleveland, OH (1964) pg. 3 Consumption of incandescent light bulbs grew rapidly in the US. In 1885, an estimated 300,000 general lighting service lamps were sold, all with carbon filaments. When tungsten filaments were introduced, about 50 million lamp sockets existed in the US. 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).Raymond Kane, Heinz Sell ''Revolution in lamps: a chronicle of 50 years of progress (2nd ed.)'', The Fairmont Press, Inc. 2001 page 37, table 2-1


Efficacy and efficiency

More than 95% of the power consumed by a typical incandescent light bulb is converted into heat rather than visible light. Other electrical light sources are more effective. For a given quantity of light, an incandescent light bulb consumes more power and emits more heat than a
fluorescent lamp A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet lig ...
. In buildings where
air conditioning Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
is used, incandescent lamps' heat output increases load on the air conditioning system. While heat from lights will reduce the need to run a building's heating system, the latter can usually produce the same amount of heat at lower cost than incandescent lights. Compared to other incandescent (non-halogen) light types, incandescent halogen lamps will emit the same amount of light using less power, and a more constant output over time, with little dimming. Luminous ''efficacy'' of a light source is the ratio of the visible light to the total power input to the source, such as a lamp. Visible light is measured in lumens, a unit which is defined in part by the differing sensitivity of the human eye to different wavelengths of light (see luminosity function). Not all wavelengths are equally effective at stimulating the human eye. The units of luminous efficacy are ''lumens per watt'' (lm/W). By definition, the maximum efficacy is 683 lm/W for monochromatic green light. A white light source with all visible wavelengths present has a lower efficacy, around 250 lumens per watt. The luminous ''efficiency'' is defined as the ratio of the luminous efficacy to the theoretical maximum luminous efficacy of 683 lm/W for green light. The chart below lists values of luminous efficacy and efficiency for some general service, 120-volt, 1000-hour lifespan incandescent bulb, and several idealized light sources. A longer chart in luminous efficacy compares a broader array of light sources. The spectrum emitted by a
blackbody A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The name "black body" is given because it absorbs all colors of light. A black body ...
radiator at temperatures of incandescent bulbs does not match the characteristics of the human eye, with most of the radiation in the range that the eye can't see. An upper limit for incandescent lamp luminous efficacy is around 52 lumens per watt, the theoretical value emitted by tungsten at its melting point.


Color rendering

The spectrum of light produced by an incandescent lamp closely approximates that of a black body radiator at the same temperature. The basis for light sources used as the standard for color perception is a tungsten incandescent lamp operating at a defined temperature. Light sources such as fluorescent lamps, high-intensity discharge lamps and
LED lamp An LED lamp or LED light bulb is an electric light that produces light using light-emitting diodes (LEDs). LED lamps are significantly more energy-efficient than equivalent incandescent lamps and can be significantly more efficient than mo ...
s have higher luminous efficiency. These devices produce light by
luminescence Luminescence is spontaneous emission of light by a substance not resulting from heat; or "cold light". 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 ...
. Their light has bands of characteristic wavelengths, without the "tail" of invisible infrared emissions, instead of the continuous spectrum produced by a thermal source. By careful selection of fluorescent phosphor coatings or filters which modify the spectral distribution, the spectrum emitted can be tuned to mimic the appearance of incandescent sources, or other different
color temperature Color temperature is the color of light emitted by an idealized opaque, non-reflective body at a particular temperature measured in kelvins. The color temperature scale is used to categorize the color of light emitted by other light sources ...
s of white light. When used for tasks sensitive to color, such as motion picture lighting, these sources may require particular techniques to duplicate the appearance of incandescent lighting. Metamerism describes the effect of different light spectrum distributions on the perception of color.


Cost of lighting

The initial cost of an incandescent bulb is small compared to the cost of the energy it uses over its lifetime. Incandescent bulbs have a shorter life than most other lighting, an important factor if replacement is inconvenient or expensive. Some types of lamp, including incandescent and fluorescent, emit less light as they age; this may be an inconvenience, or may reduce effective lifetime due to lamp replacement before total failure. A comparison of incandescent lamp operating cost with other light sources must include illumination requirements, cost of the lamp and labor cost to replace lamps (taking into account effective lamp lifetime), cost of electricity used, effect of lamp operation on heating and air conditioning systems. When used for lighting in houses and commercial buildings, the energy lost to heat can significantly increase the energy required by a building's
air conditioning Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
system. During the heating season heat produced by the bulbs is not wasted, although in most cases it is more cost effective to obtain heat from the heating system. Regardless, over the course of a year a more efficient lighting system saves energy in nearly all climates.


Measures to ban use

Since incandescent light bulbs use more energy than alternatives such as
CFL The Canadian Football League (CFL; french: Ligue canadienne de football—LCF) is a professional sports league in Canada. The CFL is the highest level of competition in Canadian football. The league consists of nine teams, each located in a ci ...
s and
LED lamp An LED lamp or LED light bulb is an electric light that produces light using light-emitting diodes (LEDs). LED lamps are significantly more energy-efficient than equivalent incandescent lamps and can be significantly more efficient than mo ...
s, many governments have introduced measures to ban their use, by setting minimum efficacy standards higher than can be achieved by incandescent lamps. Measures to ban light bulbs have been implemented in the European Union, the United States, Russia, Brazil, Argentina, Canada and Australia, among others. The European Commission has calculated that the ban contributes 5 to 10 billion euros to the economy and saves 40 TWh of electricity every year, translating in CO2 emission reductions of 15 million tonnes. Objections to banning the use of incandescent light bulbs include the higher initial cost of alternatives and lower quality of light of fluorescent lamps. Some people have concerns about the health effects of fluorescent lamps.


Efforts to improve efficacy

Some research has been carried out to improve the efficacy of commercial incandescent lamps. In 2007, General Electric 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 twice as efficient. The HEI program was terminated in 2008 due to slow progress. US Department of Energy research at Sandia 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 legislation in various countries mandating increased bulb efficiency, ''hybrid'' incandescent bulbs have been introduced by Philips. The ''Halogena Energy Saver'' incandescents can produce about 23 lm/W; about 30 percent more efficient than traditional incandescents, by using a reflective capsule to reflect formerly wasted infrared radiation back to the filament from which some is re-emitted as visible light. This concept was pioneered by Duro-Test in 1980 with a commercial product that produced 29.8 lm/W. More advanced reflectors based on
interference filter An interference filter or dichroic filter is an optical filter that reflects one or more spectral bands or lines and transmits others, while maintaining a nearly zero coefficient of absorption for all wavelengths of interest. An interference filter ...
s or photonic crystals can theoretically result in higher efficiency, up to a limit of about 270 lm/W (40% of the maximum efficacy possible). Laboratory proof-of-concept experiments have produced as much as 45 lm/W, approaching the efficacy of compact fluorescent bulbs.


Construction

Incandescent light bulbs consist of an air-tight glass enclosure (the envelope, or bulb) with a filament of tungsten wire inside the bulb, through which an electric current 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 air or gas leaks. Small wires embedded in the stem in turn support the filament and its lead wires. An electric current heats the filament to typically , well below tungsten's melting point of . Filament temperatures depend on the filament type, shape, size, and amount of current drawn. The heated filament emits light that approximates a
continuous spectrum In physics, a continuous spectrum usually means a set of attainable values for some physical quantity (such as energy or wavelength) that is best described as an interval of real numbers, as opposed to a discrete spectrum, a set of attainable ...
. The useful part of the emitted energy is visible light, but most energy is given off as heat in the near- infrared wavelengths.


Bulbs

Most light bulbs have either clear or coated glass. Coated glass bulbs have
kaolin Kaolinite ( ) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is an important industrial mineral. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral s ...
clay blown in and electrostatically deposited on the interior of the bulb. The powder layer diffuses the light from the filament. Pigments may be added to the clay to adjust the color of the light emitted. Kaolin diffused bulbs are used extensively in interior lighting because of their comparatively gentle light. Other kinds of colored bulbs are also made, including the various colors used for "party bulbs",
Christmas tree A Christmas tree is a decorated tree, usually an evergreen conifer, such as a spruce, pine or fir, or an artificial tree of similar appearance, associated with the celebration of Christmas. The custom was further developed in early modern G ...
lights and other decorative lighting. These are created by coloring the glass with a dopant; which is often a metal like
cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, pro ...
(blue) or
chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...
(green). Neodymium-containing glass is sometimes used to provide a more natural-appearing light. The glass bulb of a general service lamp can reach temperatures between . Lamps intended for high power operation or used for heating purposes will have envelopes made of hard glass or
fused quartz Fused quartz, fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non-crystalline) form. This differs from all other commercial glasses in which other ingredients are added which chang ...
. If a light bulb envelope leaks, the hot tungsten filament reacts with air, yielding an aerosol of brown
tungsten nitride Tungsten nitride (W2N, WN, WN2) 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. It is used in microelectronics as a contact material, f ...
, brown
tungsten dioxide Tungsten(IV) oxide is the chemical compound with the formula W O2. The bronze-colored solid crystallizes in a monoclinic cell. The rutile-like structure features distorted octahedral WO6 centers with alternate short W–W bonds (248 pm). E ...
, violet-blue
tungsten pentoxide Tungsten pentoxide () was reported in early literature but proved to have the stoichiometry W18O49.Wells A.F. (1984) ''Structural Inorganic Chemistry'' 5th edition Oxford Science Publications Sometimes called mineral blue, it is a blue solid form ...
, and yellow tungsten trioxide that then gets deposited on the nearby surfaces or the bulb interior.


Gas fill

Most modern bulbs are filled with an inert gas to reduce evaporation of the filament and prevent its oxidation. The gas is at a pressure of about . The gas reduces evaporation of the filament, but the fill must be chosen carefully to avoid introducing significant heat losses. For these properties, chemical inertness and high atomic or
molecular weight A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
is desirable. The presence of gas molecules knocks the liberated tungsten atoms back to the filament, reducing its evaporation and allowing it to be operated at higher temperature without reducing its life (or, for operating at the same temperature, prolongs the filament life). On the other hand, the presence of the gas leads to heat loss from the filament—and therefore efficiency loss due to reduced incandescence—by heat conduction and
heat convection Convection (or convective heat transfer) is the transfer of heat from one place to another due to the movement of fluid. Although often discussed as a distinct method of heat transfer, convective heat transfer involves the combined processes o ...
. Early lamps used only a vacuum to protect the filament from oxygen. The vacuum increases evaporation of the filament but eliminates two modes of heat loss. Some small modern lamps use vacuum as well. The most commonly used fills are: * Vacuum, used in small lamps. Provides best thermal insulation of the filament but does not protect against its evaporation. Used also in larger lamps where the outer bulb surface temperature has to be limited. *
Argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
(93%) and nitrogen (7%), where argon is used for its inertness, low thermal conductivity and low cost, and the nitrogen is added to increase the breakdown voltage and prevent arcing between parts of the filament * Nitrogen, used in some higher-power lamps, e.g. projection lamps, and where higher breakdown voltage is needed due to proximity of filament parts or lead-in wires * Krypton, which is more advantageous than argon due to its higher atomic weight and lower thermal conductivity (which also allows use of smaller bulbs), but its use is hindered by much higher cost, confining it mostly to smaller-size bulbs. * Krypton mixed with xenon, where xenon improves the gas properties further due to its higher atomic weight. Its use is however limited by its very high cost. The improvements by using xenon are modest in comparison to its cost. * Hydrogen, in special flashing lamps where rapid filament cooling is required; its high thermal conductivity is exploited here. * Halogen, a small amount mixed with inert gas. This is used in halogen lamps, which are a distinct type of incandescent lamp. The gas fill must be free of traces of water, which greatly accelerates bulb blackening (see below). The gas layer close to the filament (called the Langmuir layer) is stagnant, with heat transfer occurring only by conduction. Only at some distance does convection occur to carry heat to the bulb's envelope. The orientation of the filament influences efficiency. Gas flow parallel to the filament, e.g., a vertically oriented bulb with vertical (or axial) filament, reduces convective losses. The efficiency of the lamp increases with a larger filament diameter. Thin-filament, low-power bulbs benefit less from a fill gas, so are often only evacuated. Early light bulbs with carbon filaments also used
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...
, nitrogen, or mercury vapor. However, carbon filaments operate at lower temperatures than tungsten ones, so the effect of the fill gas was not significant as the heat losses offset any benefits.


Manufacturing

Early bulbs were laboriously assembled by hand. After automatic machinery was developed, the cost of bulbs fell. Until 1910, when Libbey's Westlake machine went into production, bulbs were generally produced by a team of three workers (two gatherers and a master gaffer) blowing the bulbs into wooden or cast-iron molds, coated with a paste. Around 150 bulbs per hour were produced by the hand-blowing process in the 1880s at Corning Glass Works. The Westlake machine, developed by Libbey Glass, was based on an adaptation of the Owens-Libbey bottle-blowing machine.
Corning Glass Works Corning Incorporated is an American multinational technology company that specializes in specialty glass, ceramics, and related materials and technologies including advanced optics, primarily for industrial and scientific applications. The c ...
soon began developing competing automated bulb-blowing machines, the first of which to be used in production was the E-Machine.


Ribbon machine

Corning continued developing automated bulb-production machines, installing the Ribbon Machine in 1926 in its Wellsboro, Pennsylvania, factory. The Ribbon Machine surpassed any previous attempts to automate bulb production and was used to produce incandescent bulbs into the 21st century. The inventor, William Woods, along with his colleague at Corning Glass Works, David E. Gray, had created a machine that by 1939 was turning out 1,000 bulbs per minute. The Ribbon Machine works by passing a continuous ribbon of glass along a
conveyor belt A conveyor belt is the carrying medium of a belt conveyor system (often shortened to belt conveyor). A belt conveyor system is one of many types of conveyor systems. A belt conveyor system consists of two or more pulleys (sometimes referred to ...
, heated in a furnace, and then blown by precisely aligned air nozzles through holes in the conveyor belt into molds. Thus the glass bulbs or envelopes are created. A typical machine of this sort can produce anywhere from 50,000 to 120,000 bulbs per hour, depending on the size of the bulb. By the 1970s, 15 ribbon machines installed in factories around the world produced the entire supply of incandescent bulbs. The filament and its supports are assembled on a glass stem, which is then 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. The 2016 closing of Osram-Sylvania's Wellsboro, Pennsylvania plant meant that one of the last remaining ribbon machines in the United States was shut down.


Filament

The first commercially successful light bulb filaments were made from carbonized paper or
bamboo Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, but ...
. Carbon filaments have a negative temperature coefficient of resistance—as they get hotter, their electrical resistance decreases. 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. Carbon filaments were "flashed" by heating in a hydrocarbon vapor (usually gasoline), to improve their strength and uniformity. Metallized or "graphitized" filaments were first heated to high temperature to transform them into graphite, which further strengthened and smoothed the filament. These filaments have a positive temperature coefficient, like a metallic conductor, which stabilized the lamps operating properties against minor variations in supply voltage. Metal filaments displaced carbon starting around 1904. Tungsten has the highest available melting point. By 1910, a process was developed by William D. Coolidge at General Electric for production of a ductile form of tungsten. The process required pressing 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 aluminium oxides at the level of a few hundred parts per million greatly improved the life and durability of the tungsten filaments.Chapter 2 ''The Potassium Secret Behind Tungsten Wire Production''


Coiled coil filament

To improve the efficiency of the lamp, the filament usually consists of multiple coils of coiled fine wire, also known as a ''coiled coil''. Light bulbs using coiled coil filaments are sometimes referred to as 'double-coil bulbs'. For a 60-watt 120-volt lamp, the uncoiled length of the tungsten filament is usually , and the filament diameter is . 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. As a result, the filament can then run hotter, which results in a more efficient light source while lasting longer than a straight filament at the same temperature. Manufacturers designate different forms of lamp filament with an alphanumeric code. Electrical filaments are also used in
hot cathode In vacuum tubes and gas-filled tubes, a hot cathode or thermionic cathode is a cathode electrode which is heated to make it emit electrons due to thermionic emission. This is in contrast to a cold cathode, which does not have a heating element. ...
s of
fluorescent lamp A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet lig ...
s and vacuum tubes as a source of electrons or in vacuum tubes to heat an electron-emitting electrode. When used as a source of electrons, they may have a special coating that increases electron production.


Reducing filament evaporation

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 1,000 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 prior to the development of incandescent and LED lamps they were useful in applications where the bulb was difficult to change. Irving Langmuir 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 is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
and some nitrogen,John Kaufman (ed.), ''IES Lighting Handbook 1981 Reference Volume'', Illuminating Engineering Society of North America, New York, 1981 page 8-6 or sometimes krypton. 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 gases have lower thermal conductivity, because both the molecular weight and cross sectional area are higher. Xenon gas improves efficiency because of its high molecular weight, but is also more expensive, so its use is limited to smaller lamps. ''Filament notching'' is due to uneven evaporation of the filament. Small variations in
resistivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
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. Since filament resistance is highly temperature-dependent, spots with higher temperature will have higher resistance, causing them to dissipate more energy, making them hotter – a positive feedback loop. These hot spots evaporate faster than the rest of the filament, permanently increasing the resistance at that point. The process ends in the familiar tiny gap in an otherwise healthy-looking filament. Lamps operated on direct current develop random stairstep irregularities on the filament surface which may cut lifespan in half compared to AC operation; different alloys of tungsten and
rhenium Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one ...
can be used to counteract the effect. Since a filament breaking in a gas-filled bulb can form an electric arc, 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 built into the light bulb. More nitrogen is used in higher-voltage lamps to reduce the possibility of arcing.


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, and is deposited preferentially on the uppermost part of the envelope, 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 emission and invention of the vacuum tube. A very small amount of water vapor inside a light bulb can significantly increase 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 is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'', ...
are placed within the lamp as a getter 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

The halogen lamp reduces uneven evaporation of the filament and eliminates darkening of the envelope by filling the lamp with a halogen gas at low pressure, along with an inert gas. The
halogen cycle A halogen lamp (also called tungsten halogen, quartz-halogen, and quartz iodine lamp) is an incandescent lamp consisting of a tungsten filament sealed in a compact transparent envelope that is filled with a mixture of an inert gas and a small ...
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. Such bulbs are much smaller than normal incandescent bulbs, and are widely used where intense illumination is needed in a limited space. Fiber-optic lamps for optical microscopy is one typical application.


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 microscopes. These arc lamps ran on relatively low voltages and incorporated tungsten filaments to start
ionization Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule ...
within the envelope. They provided the intense concentrated light of an arc lamp but were easier to operate. Developed around 1915, these lamps were displaced by mercury and xenon arc lamps.


Electrical characteristics


Power

Incandescent lamps are nearly pure resistive loads with a power factor of 1. Unlike discharge lamps or LED lamps, the power consumed is equal to the
apparent power Apparent may refer to: *Apparent magnitude, a measure of brightness of a celestial body as seen by an observer on Earth * Apparent places, the actual coordinates of stars as seen from Earth *Heir apparent, a person who is first in line of successi ...
in the circuit. Incandescent light bulbs are usually marketed according to the electrical power consumed. This depends mainly on the operating resistance of the filament. For two bulbs of the same voltage, and type, the higher-powered bulb gives more light. The table shows the approximate typical output, in lumens, of standard 120 volt incandescent light bulbs at various powers. Light output of similar 230 V bulbs is slightly less. The lower current (higher voltage) filament is thinner and has to be operated at a slightly lower temperature for the same life expectancy, which reduces energy efficiency. The lumen values for "soft white" bulbs will generally be slightly lower than for clear bulbs at the same power.


Current and resistance

The resistance of the filament is temperature dependent. The cold resistance of tungsten-filament lamps is about 1/15 the resistance when operating. For example, a 100-watt, 120-volt lamp has a resistance of 144
ohm Ohm (symbol Ω) is a unit of electrical resistance named after Georg Ohm. Ohm or OHM may also refer to: People * Georg Ohm (1789–1854), German physicist and namesake of the term ''ohm'' * Germán Ohm (born 1936), Mexican boxer * Jörg Ohm (bor ...
s when lit, but the cold resistance is much lower (about 9.5 ohms). Since incandescent lamps are resistive loads, simple phase-control
TRIAC A TRIAC (triode for alternating current; also bidirectional triode thyristor or bilateral triode thyristor) is a three terminal electronic component that conducts current in either direction when triggered. The term TRIAC is a genericised trad ...
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.


Physical characteristics


Safety

The filament in a tungsten light bulb is not easy to break when the bulb is cold, but filaments are more vulnerable when they are hot because the incandescent metal is less rigid. An impact on the outside of the bulb may cause the filament to break or experience a surge in electric current that causes part of it to melt or vaporize. In most modern incandescent bulbs, part of the wire inside the bulb acts like a
fuse Fuse or FUSE may refer to: Devices * Fuse (electrical), a device used in electrical systems to protect against excessive current ** Fuse (automotive), a class of fuses for vehicles * Fuse (hydraulic), a device used in hydraulic systems to protect ...
: if a broken filament produces an
electrical short A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit. ...
inside the bulb, the fusible section of wire will melt and cut the current off to prevent damage to the supply lines. A hot glass bulb may fracture on contact with cold objects. When the glass envelope breaks, the bulb implodes, exposing the filament to ambient air. The air then usually destroys the hot filament through oxidation.


Bulb shapes

Bulb shape and size designations are given in national standards. Some designations are one or more letters followed by one or more numbers, e.g. A55 or PAR38, where the letters identify the shape and the numbers some characteristic size. National standards such as
ANSI The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...
C79.1-2002, IS 14897:2000 and JIS C 7710:1988 cover a common terminology for bulb shapes.


Common shape codes

;General Service :Light emitted in (nearly) all directions. Available either clear or frosted. :Types: General (A), Mushroom, elliptical (E), sign (S), tubular (T) :120 V sizes: A17, 19 and 21 :230 V sizes: A55 and 60 ;High Wattage General Service :Lamps greater than 200 watts. :Types: Pear-shaped (PS) ;Decorative :lamps used in chandeliers, etc. Smaller candle-sized bulbs may use a smaller socket. :Types: candle (B), twisted candle, bent-tip candle (CA & BA), flame (F), globe (G), lantern chimney (H), fancy round (P) :230 V sizes: P45, G95 ;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), bulged reflector (BR), elliptical reflector (ER), crown-silvered :120 V sizes: R16, 20, 25 and 30 :230 V sizes: R50, 63, 80 and 95 ;Parabolic aluminized reflector (PAR) :
Parabolic aluminized reflector A parabolic aluminized reflector lamp (PAR lamp or simply PAR) is a type of electric lamp that is widely used in commercial, residential, and transportation illumination. It produces a highly directional beam. Usage includes theatrical lighti ...
(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 16, 20, 30, 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 in diameter, a PAR 20 is in diameter, PAR 30 is and a PAR 38 is in diameter. ;Multifaceted reflector (MR) :
Multifaceted reflector A multifaceted reflector (often abbreviated MR) light bulb is a reflector housing format for halogen as well as some LED and fluorescent lamps. MR lamps were originally designed for use in slide projectors, but see use in residential lighting a ...
bulbs are usually smaller in size and run at a lower voltage, often 12 V. ;HIR/IRC: "HIR" is a GE designation for a lamp with an infrared reflective coating. Since less heat escapes, the filament burns hotter and more efficiently. The Osram designation for a similar coating is "IRC".


Lamp bases

Large lamps may have a screw base or a bayonet base, with one or more contacts on the base. The shell may serve as an electrical contact or only as a mechanical support. Bayonet base lamps are frequently used in automotive lamps to resist loosening by vibration. Some tubular lamps have an electrical contact at either end. Miniature lamps may have a
wedge base upright , W2.1x9.5d base, a common 5-watt bulb in landscape lighting and some interior automotive applications such as the dome light A wedge base is a type of electrical connector used as a fitting for small light bulbs. It is similar to the ...
and wire contacts, and some automotive and special purpose lamps have screw terminals for connection to wires. Very small lamps may have the filament support wires extended through the base of the lamp for connections. A
bipin A bipin or bi-pin (sometimes referred to as two-pin, bipin cap or bipin socket) is a type of lamp fitting. They are included in the IEC standard "IEC 60061 Lamp caps and holders together with gauges for the control of interchangeability and saf ...
base is often used for halogen or reflector lamps. In the late 19th century, manufacturers introduced a multitude of incompatible lamp bases. General Electric's "
Mazda , commonly referred to as simply Mazda, is a Japanese multinational automotive manufacturer headquartered in Fuchū, Hiroshima, Japan. In 2015, Mazda produced 1.5 million vehicles for global sales, the majority of which (nearly one mi ...
" standard base sizes were soon adopted across the US. Lamp bases may be secured to the bulb with a cement, or by mechanical crimping to indentations molded into the glass bulb. Lamps intended for use in optical systems 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. Contacts in the
lightbulb socket A lightbulb socket, lightbulb holder, light socket, lamp socket or lamp holder is a device which mechanically supports and provides electrical connections for a compatible electric lamp base. Sockets allow lamps to be safely and conveniently r ...
allow the electric current to pass through the base to the filament. The socket provides electrical connections and mechanical support, and allows changing the lamp when it burns out.


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
Donald G. Fink Donald Glen Fink (November 8, 1911 – May 3, 1996) was an American electrical engineer, a pioneer in the development of radio navigation systems and television standards, vice president for research of Philco, president of the Institute of Rad ...
and H. Wayne Beaty, ''Standard Handbook for Electrical Engineers, Eleventh Edition'', McGraw-Hill, New York, 1978, , pg 22–8
A 5% reduction in voltage will double the life of the bulb, but reduce its light output by about 16%. Long-life bulbs take advantage of this trade-off in applications such as traffic signal lamps. Since electric energy they use costs more than the cost of the bulb, general service lamps emphasize efficiency over long operating life. The objective is to minimize the cost of light, not the cost of lamps. Early bulbs had a life of up to 2500 hours, but in 1924 the
Phoebus cartel The Phoebus cartel was an oligopoly that controlled the manufacture and sale of incandescent light bulbs. They appropriated market territories and lowered the useful life of such bulbs. Corporations based in Europe and the United States founded t ...
agreed to limit life to 1000 hours. When this was exposed in 1953, General Electric and other leading American manufacturers were banned from limiting the life. The relationships above are valid for only a few percent change of voltage around standard rated conditions, but they indicate that a lamp operated at low voltage could last much longer than at rated voltage, albeit with greatly reduced light output. The "
Centennial Light The Centennial Light is the world's longest-lasting light bulb, burning since 1901, and almost never turned off. It is located at 4550 East Avenue, Livermore, California, and maintained by the Livermore-Pleasanton Fire Department. Due to its lo ...
" is a light bulb that is accepted by the ''
Guinness Book of World Records ''Guinness World Records'', known from its inception in 1955 until 1999 as ''The Guinness Book of Records'' and in previous United States editions as ''The Guinness Book of World Records'', is a reference book published annually, listing world ...
'' as having been burning almost continuously at a fire station in
Livermore, California Livermore (formerly Livermorès, Livermore Ranch, and Nottingham) is a city in Alameda County, California. With a 2020 population of 87,955, Livermore is the most populous city in the Tri-Valley. It is located on the eastern edge of Californi ...
, since 1901. However, the bulb emits the equivalent light of a four watt bulb. A similar story can be told of a 40-watt bulb in Texas that has been illuminated since 21 September 1908. It once resided in an opera house where notable celebrities stopped to take in its glow, and was moved to an area museum in 1977. Photoflood lamps used for photographic lighting favor light output over life, with some lasting only two hours. The upper temperature limit for the filament is the melting point of the metal. Tungsten is the metal with the highest melting point, . A 50-hour-life projection bulb, for instance, is designed to operate only 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 of the same power rating but designed for different voltages have different luminous efficacy. For example, a 100-watt, 1000 hour, 120-volt lamp will produce about 17.1 lumens per watt. A similar lamp designed for 230 V would produce only around 12.8 lumens per watt, and one 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. File:Livermore Centennial Light Bulb.jpg, The
Centennial Light The Centennial Light is the world's longest-lasting light bulb, burning since 1901, and almost never turned off. It is located at 4550 East Avenue, Livermore, California, and maintained by the Livermore-Pleasanton Fire Department. Due to its lo ...
is the longest-lasting light bulb in the world. File:Various lighting spectrums - Flurescent incandescent diode and candle.jpg, Various lighting spectra as viewed in a diffraction grating. Upper left: fluorescent lamp, upper right: incandescent bulb, lower left: white LED, lower right: candle flame.


See also

* 3-way lamp * Flash (photography) * Lampshade * Light tube *
Lightbulb joke A lightbulb joke is a joke cycle that asks how many people of a certain group are needed to change, replace, or screw in a light bulb. Generally, the punch line answer highlights a stereotype of the target group. There are numerous versions of th ...
s *
List of light sources This is a list of sources of light, the visible part of the electromagnetic spectrum. Light sources produce photons from another energy source, such as heat, chemical reactions, or conversion of mass or a different frequency of electromagnetic ener ...
*
Longest-lasting light bulbs This is a list of the longest-lasting incandescent light bulbs. Longest-lasting light bulb The world's longest-lasting light bulb is the Centennial Light located at 4550 East Avenue, Livermore, California. It is maintained by the Livermore-Plea ...
*
Over-illumination Overillumination is the presence of lighting intensity higher than that which is appropriate for a specific activity. Overillumination was commonly ignored between 1950 and 1995, especially in office and retail environments.M.D. Simpson, ''A fl ...
* Photometry (optics) *
Resistance wire Resistance wire is wire intended for making electrical resistors (which are used to control the amount of current in a circuit). It is better if the alloy used has a high resistivity, since a shorter wire can then be used. In many situations, the ...
* Spectrometer


Explanatory notes


References


External links


Light Source Spectra
60 W-100 W Incandescent light bulb spectra, from Cornell University Program of Computer Graphics
Slow-motion video of an incandescent lightbulb filament

Ribbon machine in operation at Osram-Sylvania in 2016
{{Authority control 1878 introductions 19th-century inventions Articles containing video clips Discovery and invention controversies English inventions Thomas Edison