View source for Incandescent light bulb

{{Short description|Electric light bulb with a resistively heated wire filament}}
{{Use dmy dates|date=July 2022}}
{{Use American English|date=July 2018}}
[[File:Gluehlampe 01 KMJ.png|thumb|upright|A 230-volt incandescent light bulb with a medium-sized [[Edison screw|E27]] (Edison 27&nbsp;mm) [[Gender of connectors and fasteners|male screw]] base. The filament is visible as the mostly horizontal line between the vertical supply wires.]]
[[File:Tungsten filament.JPG|thumb|A [[scanning electron microscope]] image of the [[tungsten]] filament of an incandescent light bulb]]
[[File:Light in linger.jpg|thumb|Elaborate light in Denver, Colorado]] 

An '''incandescent light bulb''', also known as an '''incandescent lamp''' or '''incandescent light globe''', is an [[electric light]] that produces illumination by [[Joule heating]] a [[#Filament|filament]] until it [[incandescence|glows]]. The filament is enclosed in a glass bulb that is either [[vacuum|evacuated]] or filled with [[inert gas]] to protect the filament from [[oxidation]]. Electric 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 [[Regulator (automatic control)|regulating equipment]], have low [[manufacturing cost]]s, and work equally well on either [[alternating current]] 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 [[headlamp]]s, and [[flashlight]]s, and for decorative and advertising lighting.

Incandescent bulbs are much less efficient than other types of electric lighting. Less than 5% of the energy they consume is converted into visible light; the rest is released as heat.<ref name="incandescent">{{cite web |title=The Nature of Light |last=Keefe |first=T.J. |year=2007 |url=http://www.ccri.edu/physics/keefe/light.htm |access-date=5 November 2007 |archive-url=https://web.archive.org/web/20120423123823/http://www.ccri.edu/physics/keefe/light.htm |archive-date=23 April 2012}}</ref><ref>{{cite web |title=High Efficiency Incandescent Lighting {{!}} MIT Technology Licensing Office |url=https://tlo.mit.edu/technologies/high-efficiency-incandescent-lighting |website=tlo.mit.edu |access-date=19 August 2022}}</ref> The [[luminous efficacy]] of a typical incandescent bulb 16 [[Lumen (unit)|lumen]]s per watt (lm/W) for a 120&nbsp;V bulb or 13 lm/W for a 230&nbsp;V bulb, compared with 60&nbsp;lm/W for a [[Compact fluorescent lamp|compact fluorescent]] bulb or 100&nbsp;lm/W for typical white [[LED lamp]]s.<ref>[[Vincenzo Balzani]], Giacomo Bergamini, Paola Ceroni, ''Light: A Very Peculiar Reactant and Product''. In: ''[[Angewandte Chemie|Angewandte Chemie International Edition]]'' 54, Issue 39, (2015), 11320–11337, {{doi|10.1002/anie.201502325}}.</ref>

The heat produced by filaments is used in some applications, such as [[heat lamp]]s in [[incubator (egg)|incubator]]s, [[lava lamp]]s, [[Edison effect]] bulbs, and the [[Easy-Bake Oven]] toy. Quartz envelope halogen [[infrared heater]]s are used for industrial processes such as paint curing and space heating.

Incandescent bulbs typically have shorter lifetimes compared to 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]]s, [[high-intensity discharge lamp]]s, and [[LED lamp|light-emitting diode lamp]]s (LED). Some governments have begun a [[phase-out of incandescent light bulbs]] to reduce energy consumption.

==History==
Historians Robert Friedel and [[Paul Israel (historian)|Paul Israel]] list inventors of incandescent lamps prior to [[Joseph Swan]] and [[Thomas Edison]] of [[General Electric]].{{sfnp|Friedel |Israel |2010 |p=[https://books.google.com/books?id=8U-Naf4DuzMC&pg=PA91 91–93]}} They conclude that [[Edison light bulb|Edison's version]] was the first practical implementation, able to outstrip the others because of a combination of four factors: an effective [[incandescent]] material; a [[vacuum]] higher than other implementations which was achieved through the use of a [[Sprengel pump]]; a high [[Electrical resistance|resistance]] that made power distribution from a centralized source economically viable, and the development of the associated components required for a large-scale lighting system.  However, Joseph Swan's incandescent light bulb pre-dated Edison's and was sufficiently practical that it was actually installed and in daily use in London in 1881.

Historian [[Thomas P. Hughes (historian)|Thomas Hughes]] has attributed Edison's business success to his development of an entire, integrated system of electric lighting.
{{blockquote
|text=The lamp was a small component in his system of electric lighting, and no more critical to its effective functioning than the Edison Jumbo [[electrical generator|generator]], 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 [[lighting]].
|sign=Thomas P. Hughes
|source=in ''Technology at the Turning Point'', edited by W. B. Pickett<ref>{{cite book|last=Hughes|first=Thomas P.|year=1977|chapter=Edison's method|title=''Technology at the Turning Point''|editor-first=W. B.|editor-last=Pickett|place=San Francisco|publisher=San Francisco Press|pages=5–22}}</ref><ref>{{cite book|last=Hughes|first=Thomas P.|year=2004|title=American Genesis: A Century of Invention and Technological Enthusiasm|edition=2nd|place=Chicago|publisher=University of Chicago Press|isbn=978-0-22635-927-4}}</ref>}}

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! Timeline of the early evolution of the light bulb<ref>{{cite book|last=Josephson|first=Matthew|title=Edison: a biography|url=https://archive.org/details/edisonbiography00jose|url-access=registration|publisher=McGraw Hill|year=1959|isbn=0-471-54806-5}}</ref>
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{{Early evolution of the light bulb}}
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===Early pre-commercial research===
[[File:Edison Carbon Bulb.jpg|thumb|upright|Original carbon-filament bulb from [[Thomas Edison]]'s shop in Menlo Park]]
In 1761, [[Ebenezer Kinnersley]] demonstrated heating a wire to [[incandescence]].<ref>{{cite book |last=Blake-Coleman |first=B. C. (Barrie Charles) |year=1992 |title=Copper Wire and Electrical Conductors – The Shaping of a Technology |url=https://books.google.com/books?id=xMvY_v4kMMQC&pg=PA127 |publisher=Harwood Academic Publishers |page=127 |isbn=3-7186-5200-5 |url-status=live |archive-url=https://web.archive.org/web/20171206142310/https://books.google.com/books?id=xMvY_v4kMMQC&pg=PA127 |archive-date=6 December 2017}}</ref> However such wires tended to melt or oxidize very rapidly (burn) in the presence of air.{{sfnp|Friedel |Israel |2010 |p= [https://books.google.com/books?id=8U-Naf4DuzMC&pg=PA6 6–7]}} [[Limelight]] became a popular form of [[stage lighting]] in the early 19th century, by heating a piece of [[calcium oxide]] to incandescence with an [[oxyhydrogen torch]].<ref>{{Cite web|url=https://www.aps.org/apsnews/2018/11/1825-public-demonstration-of-the-limelight|title=November 9, 1825: Public Demonstration of the Limelight|website=www.aps.org}}</ref>

In 1802, [[Humphry Davy]] used what he described as "a [[Battery (electricity)|battery]] of immense size",<ref>{{cite book|last1=Jones|first1=Bence|title=The Royal Institution: Its Founder and Its First Professors|date=2011|publisher=[[Cambridge University Press]]|isbn=978-1108037709|page=278}}</ref> consisting of 2,000 cells housed in the basement of the [[Royal Institution]] of Great Britain,<ref>{{cite web|title=Popular Science Monthly (Mar-Apr 1879)|url=https://en.wikisource.org/wiki/Popular_Science_Monthly/Volume_14|website=Wiki Source|access-date=1 November 2015|url-status=live|archive-url=https://web.archive.org/web/20150910091549/https://en.wikisource.org/wiki/Popular_Science_Monthly/Volume_14|archive-date=10 September 2015}}</ref> to create an incandescent light by passing the current through a thin strip of [[platinum]], 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.<ref name=Davis>Davis, L.J. "Fleet Fire." Arcade Publishing, New York, 2003. {{ISBN|1-55970-655-4}}</ref> Davy also demonstrated the [[electric arc]], by passing high current between two pieces of charcoal.

For the next 40 years much research was given to turning the [[carbon arc lamp]] into a practical means of lighting.{{sfnp|Friedel |Israel |2010 |p= [https://books.google.com/books?id=8U-Naf4DuzMC&pg=PA6 6–7]}} The carbon arc itself was dim and violet in color, emitting most of its energy in the [[ultraviolet]], but the positive electrode was heated to just below the melting point of carbon and glowed very brightly with incandescence very close to that of sunlight.<ref>''Clinical Medicine and Surgery Volume 35'' by Herman Goodman - American Journal of Clinical Medicine, 1928, Page 159-161</ref> Arc lamps burned up their carbon rods very rapidly, expelled dangerous [[carbon monoxide]], and tended to produce outputs in the tens of kilowatts. Therefore, they were only practical for lighting large areas, so researchers continued to search for a way to make lamps suitable for home use.{{sfnp|Friedel |Israel |2010 |p= [https://books.google.com/books?id=8U-Naf4DuzMC&pg=PA6 6–7]}}

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.<ref name=HoustonCh2/>

In 1835, [[James Bowman Lindsay]] 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.<ref name=Challoner>{{cite book|last=Challoner|first=Jack|title=1001 Inventions That Changed The World|publisher=Barrons Educational Series|location=Hauppauge NY|year=2009|page=305|display-authors=etal|isbn=978-1844036110}}</ref>

In 1838, Belgian lithographer [[Marcellin Jobard]] invented an incandescent light bulb with a vacuum atmosphere using a carbon filament.{{sfnp|Friedel |Israel |2010 |p=[https://books.google.com/books?id=8U-Naf4DuzMC&pg=PA91 91]}}

In 1840, British scientist [[Warren De la Rue]] enclosed a coiled platinum filament in a [[vacuum]] tube and passed an electric current through it.<ref name="peke22">{{cite web |title=Who invented the lightbulb? |first1=Elizabeth |last1=Peterson |first2=Callum |last2=McKelvie |date=2022-11-03 |website=Live Science |url=https://www.livescience.com/43424-who-invented-the-light-bulb.html |access-date=2024-11-16 }}</ref> 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.{{sfnp|Houston |Kennely |1896 |p=[https://archive.org/details/electricincande00kenngoog/page/n35/mode/2up 24]}}{{sfnp|Friedel |Israel |2010 |p=[https://books.google.com/books?id=8U-Naf4DuzMC&pg=PA7 7]}}

In 1845, American [[John Wellington Starr|John W. Starr]] patented an incandescent light bulb using carbon filaments.<ref>[[Charles D. Wrege]] ''J.W. Starr: Cincinnati's Forgotten Genius'', Cincinnati Historical Society Bulletin 34 (Summer 1976): 102–120. Retrieved 16 February 2010.</ref><ref>{{cite book|last1=Derry|first1=T.K.|last2=Williams|first2=Trevor|title=A Short History of Technology|year=1960|publisher=Oxford University Press|isbn=0-486-27472-1}}</ref> His invention was never produced commercially.<ref>[https://web.archive.org/web/20030713033647/http://home.frognet.net/~ejcov/starr.html "John Wellington Starr"]. Retrieved 16 February 2010.</ref>{{Better source needed|date=November 2024}}

In 1851, [[Jean Eugène Robert-Houdin]] 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]].{{efn|1=Many of the above lamps are illustrated and described in the 1896 book ''Electric Incandescent Lighting''<ref name=HoustonCh2>{{cite book |first1=Edwin J. |last1=Houston |first2=A. E. |last2=Kennely |name-list-style=amp |title=Electric Incandescent Lighting |publisher=The W. J. Johnston Company |location=New York |year=1896 |pages=[https://archive.org/details/electricincande00kenngoog/page/n29 18–42] |via=Internet Archive}}</ref>}}

In 1859, [[Moses G. Farmer]] built an electric incandescent light bulb using a platinum filament.<ref>{{cite book |title=A Streak of Luck |first=Robert |last=Conot |publisher=Seaview Books |location=New York |year=1979 |isbn=0-87223-521-1 |pages=120–121 |url=https://archive.org/details/streakofluckcono00cono/page/120 }}</ref> Thomas Edison later saw one of these bulbs in a shop in Boston, and asked Farmer for advice on the electric light business.

[[File:Stamp of USSR 1634g.jpg|thumb|right|upright|[[Alexander Lodygin]] on 1951 Soviet postal stamp]]
In 1872, Russian [[Alexander Nikolayevich Lodygin|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.<ref>''Edison Electric Light Co. vs. United States Electric Lighting Co.'', Federal Reporter, F1, Vol. 47, 1891, p. 457.</ref> Later he lived in the US, changed his name to Alexander de Lodyguine and applied for and obtained patents for incandescent lamps having [[chromium]], [[iridium]], [[rhodium]], [[ruthenium]], [[osmium]], [[molybdenum]] and [[tungsten]] filaments.<ref>{{US patent|575002|U.S. Patent 575,002 ''Illuminant for Incandescent Lamps'' by A. de Lodyguine. Application on 4 January 1893}}</ref>

On 24 July 1874, a Canadian patent was filed by [[Henry Woodward (inventor)|Henry Woodward]] and [[Mathew Evans]] 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<ref>{{US patent|181,613}}</ref> to Thomas Edison in 1879. (Edison needed ownership of the novel claim of lamps connected in a parallel circuit.)<ref>{{cite web|title=Patent no. 3738. Filing year 1874: Electric Light|url=http://www.collectionscanada.gc.ca/innovations/023020-2710-e.html|publisher=[[Library and Archives Canada]]|access-date=17 June 2013|url-status=dead|archive-url=https://web.archive.org/web/20130619071150/http://www.collectionscanada.gc.ca/innovations/023020-2710-e.html|archive-date=19 June 2013}}</ref><ref>{{cite web|url=http://home.frognet.net/~ejcov/evans.html|archive-url=https://web.archive.org/web/20050219182908/http://home.frognet.net/~ejcov/evans.html|url-status=dead|archive-date=19 February 2005|title=Henry Woodward and Mathew Evans Lamp retrieved 2010 February 16|work=frognet.net}}</ref> The government of Canada maintains that it is Woodward and Evans who invented the lightbulb.<ref>{{Cite book |last=Immigration, Refugees and Citizenship Canada |author-link=Immigration, Refugees and Citizenship Canada |date=2021 |title=Discover Canada: The Rights and Responsibilities of Citizenship |publisher=Immigration, Refugees and Citizenship Canada = Immigration, réfugiés et citoyenneté Canada |url=https://www.canada.ca/content/dam/ircc/migration/ircc/english/pdf/pub/discover.pdf |access-date=2024-08-15 |isbn=978-0-660-39273-8}}</ref>
<!--Anything after 1877 belongs in a later section.-->

===Commercialization===

====Carbon filament and vacuum====
[[File:carbonfilament.jpg|thumb|left|Carbon filament lamps, showing darkening of bulb]]
[[File:Joseph Wilson Swan.jpg|thumb|upright|[[Sir Joseph Wilson Swan]]]]
[[Joseph Swan]] (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.<ref name="guarnieri 7-1">{{Cite journal|last=Guarnieri|first=M.|year=2015|title=Switching the Light: From Chemical to Electrical|journal=IEEE Industrial Electronics Magazine|volume=9|issue=3|pages=44–47|doi=10.1109/MIE.2015.2454038|bibcode=2015IIEM....9c..44G |hdl=11577/3164116|s2cid=2986686|url=https://www.research.unipd.it/bitstream/11577/3164116/5/21%20LightElectric.pdf|hdl-access=free|access-date=2 September 2019|archive-date=14 February 2022|archive-url=https://web.archive.org/web/20220214220606/https://www.research.unipd.it/retrieve/handle/11577/3164116/225053/21%20LightElectric.pdf|url-status=live | issn=1932-4529 }}</ref>

[[File:Sir Joseph Swan blue plaque.jpg|thumb|Historical plaque at [[Underhill, Low Fell, Gateshead|Underhill]], the first house to be lit by electric lights]]
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.<ref name="Incandescent Electric Lamp 21-25">{{cite book |last=Swan |first=K R |title=Sir Joseph Swan and the Invention of the Incandescent Electric Lamp |year=1946 |publisher=Longmans, Green and Co. |pages=21–25}}</ref> 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.<ref name=RSoC>{{Cite web |website=Royal society of chemistry |title=Reward offered for oldest working light bulb in a British home |date=30 January 2009 |url=https://www.rsc.org/news-events/articles/2009/01-january/light-bulb/ |access-date=9 March 2025}}</ref> It was also shown to 700 who attended a meeting of the [[Literary and Philosophical Society of Newcastle upon Tyne]] on 3 February 1879.<ref name=WIRED>{{cite magazine |title=Dec. 18, 1878: Let There Be Light — Electric Light |url=https://www.wired.com/2009/12/1218joseph-swan-electric-bulb/ |date=18 December 2009 |magazine=WIRED |url-status=live |archive-url=https://web.archive.org/web/20161021003405/https://www.wired.com/2009/12/1218joseph-swan-electric-bulb/ |archive-date=21 October 2016}}</ref><ref name=RSoC/> The society's building was the first public building to be lit by electricity. The lamps Swan demonstrated 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.<ref name=WIRED/>

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.<ref name="Incandescent Electric Lamp 21-25"/> 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.<ref>R.C. Chirnside. Sir Joseph Wilson Swan FRS – The Literary and Philosophical Society of Newcastle upon Tyne 1979.</ref> In 1881, the [[Savoy Theatre]] in the [[City of Westminster]], 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.<ref name=Times>"The Savoy Theatre", ''[[The Times]]'', 3 October 1881</ref> The first street in the world to be lit by an incandescent lamps was Mosley Street, [[Newcastle upon Tyne]], [[United Kingdom]] in 1880.<ref>{{cite web |url=http://www.ncl.ac.uk/library/special-collections/exhibitions/current-and-past-exhibitions/very_truly_yours/science/swan/electric_light/ |title=Electric lighting |publisher=Newcastle University Library |date=23 October 2013|url-status=dead |archive-url=https://web.archive.org/web/20140606212620/http://www.ncl.ac.uk/library/special-collections/exhibitions/current-and-past-exhibitions/very_truly_yours/science/swan/electric_light/ |archive-date=6 June 2014}}</ref><ref>[[:commons:File:Sir Joseph William Swan FRS (RSC National Chemical Landmark).jpg|Sir Joseph William Swan FRS (RSC National Chemical Landmark)]]{{Circular reference|date=September 2021}}</ref>
[[File:Edison, Maxim, and Swan bulbs.svg|thumb|Comparison of Edison, Maxim, and Swan bulbs, 1885]]
[[File:Edison incandescent lights.jpg|thumb|left|Edison carbon filament lamps, early 1880s]]
[[File:Thomas edison glühbirne Getty 450854582.jpg|thumb|upright|[[Thomas Alva Edison]]]]
[[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.<ref>{{US patent|0214636}}.</ref> After many experiments, first with [[carbon]] in the early 1880s and then with [[platinum]] and other metals, in the end Edison returned to a carbon filament.<ref>{{Cite book |title=The story of great inventions |last=Burns |first=Elmer Ellsworth |url=https://archive.org/details/storygreatinven01burngoog |page=[https://archive.org/details/storygreatinven01burngoog/page/n146 123] |year=1910 |publisher=[[Harper & Brothers]]}}</ref> The first successful test was on 22 October 1879,<ref>{{cite book |first=Paul |last=Israel |title=Edison: a Life of Invention |url=https://archive.org/details/edisonlifeofinve0000isra |url-access=registration |publisher=Wiley |year=1998 |page=[https://archive.org/details/edisonlifeofinve0000isra/page/186 186]}}</ref><ref>{{cite web|title=Thomas Edison: Original Letters and Primary Sources |url=http://www.shapell.org/btl.aspx?2718806 |publisher=Shapell Manuscript Foundation |url-status=live |archive-url=https://web.archive.org/web/20120119173416/http://www.shapell.org/btl.aspx?2718806 |archive-date=19 January 2012}}</ref> 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."<ref name=Patent898>{{US patent|0223898}} granted 27 January 1880</ref> Although the patent described several ways of creating the carbon filament including using "cotton and linen thread, wood splints, papers coiled in various ways,"<ref name="Patent898"/> Edison and his team later discovered that a carbonized bamboo filament could last more than 1200 hours.<ref>{{cite book |last=Levy |first=Joel |title=Really useful: the origins of everyday things |year=2002 |publisher=Firefly Books |location=New York |isbn=9781552976227 |page=[https://archive.org/details/reallyusefulorig00levy/page/124 124] |url=https://archive.org/details/reallyusefulorig00levy|url-access=registration |quote=bamboo filament edison patent 1200. }}</ref> In 1880, the [[Oregon Railroad and Navigation Company]] steamer, [[SS Columbia (1880)|''Columbia'']], became the first application for Edison's incandescent electric lamps (it was also the first ship to use a [[dynamo]]).<ref>{{cite book |last=Belyk |first=Robert C. |title=Great Shipwrecks of the Pacific Coast |location=New York |publisher=Wiley |year=2001 |isbn=0-471-38420-8}}</ref><ref>{{cite book |last=Jehl |first=Francis |url=https://books.google.com/books?id=FSNVAAAAMAAJ&q=ss+columbia |title=Menlo Park reminiscences, Volume 2 |publisher=Edison's institute |year=1936 |page=564 |access-date=18 October 2020 |archive-date=3 January 2021 |archive-url=https://web.archive.org/web/20210103065132/https://books.google.com/books?id=FSNVAAAAMAAJ&q=ss+columbia |url-status=live }}</ref><ref name="Dalton">{{cite book |last=Dalton |first=Anthony |url=https://books.google.com/books?id=LOQ67VeU3WwC&pg=PA63 |title=A Long, Dangerous Coastline: Shipwreck Tales from Alaska to California |publisher=Heritage House Publishing Company |year=2011 |page=63 |isbn=9781926936116 |access-date=18 October 2016 |archive-date=22 May 2020 |archive-url=https://web.archive.org/web/20200522055052/https://books.google.com/books?id=LOQ67VeU3WwC&pg=PA63 |url-status=live }}</ref>

Albon Man, a New York lawyer, started [[Electro-Dynamic Light Company]] in 1878 to exploit his patents and those of [[William E. Sawyer|William Sawyer]].<ref name=EE1890>{{cite book |title=Electrical Engineer, Volume 10 |chapter=Reports of Companies |chapter-url=https://books.google.com/books?id=GbNNAQAAMAAJ&pg=PA72 |date=16 July 1890 |publisher=Electrical Engineer |quote=The Consolidated Company was the successor of the Electro-Dynamic Light Company of New York, the first company organized in the United States for the manufacture and sale of electric incandescent lamps, and the owner of a large number of patents of date prior to those upon which rival companies were depending. ... The United States Electric Lighting Company was organized in 1878, a few weeks after the Electro-Dynamic Company |page=72 |access-date=18 October 2016 |archive-date=26 January 2017 |archive-url=https://web.archive.org/web/20170126140751/https://books.google.com/books?id=GbNNAQAAMAAJ&pg=PA72 |url-status=live }}</ref><ref name=ER1890>{{cite book |title=Electrical Review, Volume 16 |chapter=Electric Light News |chapter-url=https://books.google.com/books?id=wdVFAQAAMAAJ&pg=RA3-PA9 |date=19 July 1890 |publisher=Delano |quote=The United States Electric Lighting Company was organized in 1878, a few weeks after the Electro-Dynamic Light Company |page=9 |access-date=18 October 2016 |archive-date=27 January 2017 |archive-url=https://web.archive.org/web/20170127181438/https://books.google.com/books?id=wdVFAQAAMAAJ&pg=RA3-PA9 |url-status=live }}</ref> Weeks later the [[United States Electric Lighting Company]] was organized.<ref name=EE1890/><ref name=ER1890/><ref name=WE1890>{{cite book |title=Western Electrician |chapter=The Westinghouse Electric Company |chapter-url=https://books.google.com/books?id=m3oxAQAAMAAJ&pg=RA1-PA36 |date=19 July 1890 |publisher=Electrician Publishing Company |quote=The United States Electric Lighting Company was organized in 1878 a few weeks after the Electro-Dynamic company, and was the successor of the oldest company in the United States for the manufacture of electric power apparatus |page=36 |access-date=18 October 2016 |archive-date=27 January 2017 |archive-url=https://web.archive.org/web/20170127060947/https://books.google.com/books?id=m3oxAQAAMAAJ&pg=RA1-PA36 |url-status=live }}</ref> This company did not 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]] was the chief engineer at the US Electric Lighting Co.<ref>The National Cyclopedia of American Biography, Vol VI 1896, p. 34</ref> 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 (company)|Finlayson]]'s textile factory in [[Tampere, Finland]] in March 1882.<ref>{{cite web|url=http://innovationcapital.fi/innovation-story/a-history-of-continuous-change-and-innovation|title=A history of continuous change and innovation|first=Mika|last=Kautonen|work=Smart Tampere Ecosystem|date=18 November 2015|access-date=9 December 2021|archive-date=9 December 2021|archive-url=https://web.archive.org/web/20211209035220/http://innovationcapital.fi/innovation-story/a-history-of-continuous-change-and-innovation|url-status=live}}</ref>

On 4 March 1880, just five months after Edison's light bulb, [[Alessandro Cruto]] developed a process to create thin carbon filaments by heating thin platinum filaments in the presence of gaseous [[ethyl alcohol]] to coat them with pure graphite, and then [[Sublimation (phase transition)|sublimating]] the platinum at high temperatures. In 1882 at the Munich Electrical Exhibition in Bavaria, Germany Cruto demonstrated bulbs that were more efficient than Edison's and produced a better, whiter light.<ref>https://ilglobo.com/news/alessandro-crutos-incandescent-light-bulb-33135/ {{dead link|date=February 2022}}</ref>

[[Lewis Latimer]], 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.<ref>{{US patent|252386|U.S. Patent 252, 386 ''Process OF Manufacturing Carbons.'' by Lewis H. Latimer. Application on 19 February 1881}}</ref> Latimer patented other improvements such as a better way of attaching filaments to their wire supports.<ref name="Fouché">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. {{ISBN|0-8018-7319-3}}</ref>

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 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]] in June 1882.

[[File:Light bulb.png|thumb|left|upright|{{US patent|0223898}} by [[Thomas Edison]] for an improved electric lamp, 27 January 1880]]
The [[United States Patent and Trademark Office|United States Patent Office]] gave a ruling 8 October 1883, that Edison's patents were based on the prior art of [[William E. Sawyer|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.<ref>Consol. Elec. Light Co v. McKeesport Light Co, 40 F. 21 (C.C.W.D. Pa. 1889) aff'd, 159 U.S. 465, 16 S. Ct. 75, 40 L. Ed. 221 (1895).</ref>

In 1893, [[Heinrich Göbel]] claimed he had designed the first incandescent light bulb in 1854, with a thin carbonized [[bamboo]] 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 (patent law)|anticipation]], but there was never a decision in a final hearing due to the expiration of Edison's patent. Research work published in 2007 concluded that the story of the Göbel lamps in the 1850s is fictitious.<ref name="roh07">{{cite book |first=Hans-Christian |last=Rohde |title=Die Göbel-Legende – Der Kampf um die Erfindung der Glühlampe |language=de |publisher=zu Klampen |location=Springe |year=2007 |isbn=978-3-86674-006-8 |oclc=85243650}}</ref>

The main difficulty with evacuating the lamps was moisture inside the bulb, which [[Water splitting|split]] when the lamp was lit, with resulting oxygen attacking the filament.<ref name="lamptech">{{cite web|url=http://www.lamptech.co.uk/Documents/IN%20Getters.htm |title=Getters |publisher=Lamptech.co.uk |date= |access-date=2022-08-18}}</ref> In the 1880s, [[phosphoric anhydride]] was used in combination with expensive [[mercury vacuum pump]]s.<ref name="HS1927">{{cite web | url=https://bulbs.2yr.net/history-of-the-incandescent-lamp-chapter4.php | title=2yr.net - Antique & Vintage Light Bulb Collection Museum - History of the Incandescent Lamp - by John W. Howell and Henry Schroeder (1927) Chapter 4: The Vacuum, Getters and the Gas Filled Lamp }}</ref> However, about 1893, Italian inventor {{ill|Arturo Malignani|it}} (1865–1939), who lacked these pumps, discovered that phosphorus vapours did the job of chemically binding the remaining amounts of water and oxygen.<ref name="lamptech" /><ref name="HS1927" /> In 1896 he patented a process of introducing [[red phosphorus]] as the so-called [[getter]]  inside the bulb <ref name="lamptech" />), which allowed obtaining economic bulbs lasting 800 hours; his patent was acquired by Edison in 1898.<ref name="guarnieri 7-1"/>

In 1897, German physicist and chemist [[Walther Nernst]] developed the [[Nernst lamp]], a form of incandescent lamp that used a ceramic [[globar]] and did not require enclosure in a vacuum or inert gas.<ref>{{cite journal |first=Allan |last=Mills |title=The Nernst Lamp. Electrical Conductivity in Non-Metallic Materials |journal=ERittenhouse |volume=24 |issue=1 |date=June 2013 |url=http://www.erittenhouse.org/artitcles/the-nernst-lamp/ |url-status=live |archive-url=https://web.archive.org/web/20130717015135/http://www.erittenhouse.org/artitcles/the-nernst-lamp/ |archive-date=17 July 2013}}</ref><ref>{{cite web |title=Walther Nernst Chronology |url=http://www.nernst.de/chronology.htm |work=nernst.de |access-date=18 January 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150222122341/http://nernst.de/chronology.htm |archive-date=22 February 2015}}</ref> Twice as efficient as carbon filament lamps, Nernst lamps were briefly popular until overtaken by lamps using metal filaments.

==== Metal filament, inert gas ====
[[File:Squirrel Cage filament lamp.jpg|thumb|upright|A tantalum lamp with a 1 meter long filament.]]

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.<ref>I. C. S. Reference Library Volume 4B, Scranton, [[International Textbook Company]], 1908, no ISBN</ref> 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.<ref>{{cite web|title=GE Tantalum Filament 25W of American Design|url=http://www.lamptech.co.uk/Spec%20Sheets/IN%20TA%20GE%2025W.htm|publisher=Museum of Electric Lamp Technology|access-date=17 June 2013|url-status=live|archive-url=https://web.archive.org/web/20121113175731/http://www.lamptech.co.uk/Spec%20Sheets/IN%20TA%20GE%2025W.htm|archive-date=13 November 2012}}</ref>

From 1898 to around 1905, [[osmium]] was also used as a filament in lamps made by [[Carl Auer von Welsbach]]. The metal was so expensive that used lamps could be returned for partial credit.<ref>{{cite web|url=http://home.frognet.net/~ejcov/osmium.html|title=The Osmium Filament Lamp|work=frognet.net |url-status=dead|archive-url=https://web.archive.org/web/20081012030517/http://home.frognet.net/~ejcov/osmium.html |archive-date=12 October 2008}}</ref> It could not be made for 110&nbsp;V or 220&nbsp;V so several lamps were wired in series for use on standard voltage circuits. These were primarily sold in Europe.

====Tungsten filament====
[[File:Dr. Just Sándor és Hanaman Ferenc.jpg|thumb|upright|Hanaman (left) and Just (right), the inventors of the tungsten bulbs]]
[[File:Tungsram advertisement.jpg|thumb|upright|[[Hungarian language|Hungarian]] advertising of the [[Tungsram]]-bulb from 1906. This was the first light bulb that used a filament made from [[tungsten]] instead of carbon. The inscription reads: ''wire lamp with a drawn wire – indestructible''.]]

On 13 December 1904, [[Hungary|Hungarian]] [[Sándor Just]] and [[Croats|Croatian]] [[Franjo Hanaman]] were granted a Hungarian patent (No. 34541) for a [[tungsten]] filament lamp that lasted longer and gave brighter light than the carbon filament.<ref name="guarnieri 7-1"/> Tungsten filament lamps were first marketed by the [[Hungary|Hungarian]] company [[Tungsram]] in 1904. This type is often called Tungsram-bulbs in many European countries.<ref>{{cite web|title=The History of Tungsram|archive-url=https://web.archive.org/web/20050530094858/http://www.tungsram.hu/tungsram/downloads/tungsram/tu_short_history_1896-1996.pdf |archive-date=30 May 2005|url=http://www.tungsram.hu/tungsram/downloads/tungsram/tu_short_history_1896-1996.pdf}}</ref> Filling a bulb with an [[inert gas]] such as [[argon]] 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 [[Luminous efficacy|efficacy]] with less reduction in filament life.<ref>{{cite book|last1=Giridharan|first1=M. K.|title=Electrical Systems Design|date=2010|publisher=I. K. International|location=New Delhi|isbn=9789380578057|page=25|url=https://books.google.com/books?id=Tt6G60zZF3cC&pg=PA25|url-status=live|archive-url=https://web.archive.org/web/20160102022536/https://books.google.com/books?id=Tt6G60zZF3cC&pg=PA25&lpg=PA25|archive-date=2 January 2016}}</ref>

In 1906, [[William D. Coolidge]] developed a method of making "ductile tungsten" from [[sintered]] [[tungsten]] which could be made into filaments while working for [[General Electric|General Electric Company]].<ref>{{cite journal|doi=10.1557/S0883769400045164| journal = MRS Bulletin| volume =20 | issue = 8 | year = 1995 | pages = 67–73| title = The Coolidge Process for Making Tungsten Ductile: The Foundation of Incandescent Lighting | first1 = C.L. |last1= Briant and | first2 =Bernard P. | last2=Bewlay| bibcode = 1995MRSBu..20...67B| s2cid = 138257279}}</ref> By 1911 General Electric had begun selling incandescent light bulbs with ductile tungsten wire.<ref>{{Cite book|last1=Nair|first1=Govind B.|url=https://books.google.com/books?id=znbhDwAAQBAJ&q=By+1911+incandescent+light+bulbs+with+ductile+tungsten+wire&pg=PA22|title=The Fundamentals and Applications of Light-Emitting Diodes: The Revolution in the Lighting Industry|last2=Dhoble|first2=Sanjay J.|date=9 July 2020|publisher=Woodhead Publishing|isbn=978-0-12-823161-6|page=22|language=en|access-date=5 August 2021|archive-date=17 August 2021|archive-url=https://web.archive.org/web/20210817015813/https://books.google.com/books?id=znbhDwAAQBAJ&q=By+1911+incandescent+light+bulbs+with+ductile+tungsten+wire&pg=PA22|url-status=live}}</ref>

In 1913, [[Irving Langmuir]] found that filling a lamp with [[inert gas]] (nitrogen at first, and later argon) instead of a vacuum resulted in twice the luminous efficacy and reduced bulb blackening.{{citation needed|date=January 2021}} He patented his device on April 18, 1916.<ref>{{Cite web|url=https://www.aps.org/archives/publications/apsnews/200304/history.cfm|title=This Month in Physics History|website=www.aps.org}}</ref>

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]].<ref>{{cite web|title=Burnie Lee Benbow|url=http://home.frognet.net/~ejcov/benbow10.html|website=frognet|access-date=19 February 2017|url-status=dead|archive-url=https://web.archive.org/web/20120612194145/http://home.frognet.net/~ejcov/benbow10.html|archive-date=12 June 2012}}</ref><ref>Benbow, B.L., {{US patent|1247068|US patent 1247068: "Filament"}}, filed 4 October 1913</ref> 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.<ref>{{cite web|title=Trial Production of the World's First Double-Coil Bulb|url=http://toshiba-mirai-kagakukan.jp/en/learn/history/ichigoki/1921lamp/index.htm|website=Toshiba|publisher=TOSHIBA CORP|access-date=19 February 2017|url-status=live|archive-url=https://web.archive.org/web/20170219184124/http://toshiba-mirai-kagakukan.jp/en/learn/history/ichigoki/1921lamp/index.htm|archive-date=19 February 2017}}</ref>

Between 1924 and the outbreak of the Second World War, the [[Phoebus cartel]] attempted to fix prices and sales quotas for bulb manufacturers outside of North America.<ref name=ieee-bulb>{{Cite journal
  |title=The Great Lightbulb Conspiracy
  |journal=[[IEEE Spectrum]]
  |date=24 September 2014
|author=Markus Krajewski
  |url=https://spectrum.ieee.org/the-great-lightbulb-conspiracy
  |access-date=3 November 2017
|archive-url=https://web.archive.org/web/20171029040239/https://spectrum.ieee.org/tech-history/dawn-of-electronics/the-great-lightbulb-conspiracy
  |archive-date=29 October 2017
|url-status=live
  }}</ref>

In 1925, [[Marvin Pipkin]], an American chemist, patented a process for [[Frosted glass|frost]]ing the inside of lamp bulbs without weakening them.<ref name=10Kaccident>{{cite magazine |last= Payne |first= Kenneth Wilcox |date= 1927 |title= A $10,000 Accident |url= https://books.google.com/books?id=ICoDAAAAMBAJ&q=%22Marvin+Pipkin%22+awarded+the+Charles+A.+Coffin+award&pg=PA24 |page= 24 |magazine= Popular Science |location= New York City |publisher= Bonnier Corporation |access-date= 31 July 2020 |archive-date= 4 February 2021 |archive-url= https://web.archive.org/web/20210204021048/https://books.google.com/books?id=ICoDAAAAMBAJ&q=%22Marvin+Pipkin%22+awarded+the+Charles+A.+Coffin+award&pg=PA24 |url-status= live }}</ref> In 1947, he patented a process for coating the inside of lamps with [[silica]].<ref>{{cite journal |last=Bonnier Corp |title=Popular Science |journal=The Popular Science Monthly |url=https://books.google.com/books?id=lSQDAAAAMBAJ&pg=PA125 |date=March 1949 |page=125 |publisher=Bonnier Corporation |issn=0161-7370 |access-date=4 January 2021 |archive-date=4 February 2021 |archive-url=https://web.archive.org/web/20210204011225/https://books.google.com/books?id=lSQDAAAAMBAJ&pg=PA125 |url-status=live }}</ref>

In 1930, [[Hungary|Hungarian]] [[Imre Bródy]] 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]] in 1937, in a factory co-designed by Polányi and Hungarian-born physicist [[Egon Orowan]].<ref>{{cite web|url=http://energyhistory.energosolar.com/en_20th_century_electric_history.htm |title=Ganz and Tungsram – the 20th century|archive-url=https://web.archive.org/web/20090330212227/http://energyhistory.energosolar.com/en_20th_century_electric_history.htm |archive-date=30 March 2009}}</ref>{{Full citation needed |date=November 2024}}

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.<ref name="GETP110">''Incandescent Lamps, Publication Number TP-110'', General Electric Company, Nela Park, Cleveland, OH (1964) pg. 3</ref>

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).<ref name=Kane2001>Raymond Kane, Heinz Sell ''Revolution in lamps: a chronicle of 50 years of progress (2nd ed.)'', The Fairmont Press, Inc. 2001 {{ISBN|0-88173-378-4}} page 37, table 2-1</ref>

==Efficacy and efficiency==
{{further|Luminous efficacy}}
[[File:2200K Spectrum.jpg|thumb|Spectrum of an incandescent lamp at 2200&nbsp;K, showing most of its emission as invisible [[infrared]] light]]
[[File:Thermal image of an incandescent light.jpg|thumb|Thermal image of an incandescent bulb. {{convert|22|–|175|C|F}}. Most of the mid and far-IR is absorbed by the glass, heating it to scorching temperatures. This heats the surrounding air, which rises, helping cool the bulb from the bottom up.]]
Less than 5% of the power consumed by a typical incandescent light bulb is converted into visible light, with most of the rest being emitted as invisible infrared radiation.<ref name="incandescent"/><ref>''Handbook of Digital Image Synthesis'' by Vincent Pegoraro - CRC Press 2017 Page 690</ref> Light bulbs are rated by their [[luminous efficacy]], which is the ratio of the amount of visible light emitted ([[luminous flux]]) to the electrical power consumed.<ref>{{cite book |title=IEEE Standard 100: definition of luminous efficacy |page=647}}</ref> Luminous efficacy is measured in [[Lumen (unit)|lumens]] per watt (lm/W).

The luminous ''efficiency'' of a source is defined as the ratio of its luminous efficacy to the maximum possible luminous efficacy, which is 683&nbsp;lm/W.<ref>{{cite web |url=http://www.yuvaengineers.com/end-of-incandescent-light-bulb/ |title=End of Incandescent Light Bulb |publisher=yuvaengineers.com |date=23 June 2012 |access-date=7 March 2017 |url-status=live |archive-url=https://web.archive.org/web/20170307124220/http://www.yuvaengineers.com/end-of-incandescent-light-bulb/ |archive-date=7 March 2017}}</ref><ref>{{cite web |url=http://www.kse-lights.co.uk/the-energy-efficiency-of-light-bulbs-today-compared-to-the-past/ |title=The Energy Efficiency of Light Bulbs Today Compared to the Past |publisher=kse-lights.co.uk |date=13 February 2017 |access-date=7 March 2017 |url-status=dead |archive-url=https://web.archive.org/web/20170307123653/http://www.kse-lights.co.uk/the-energy-efficiency-of-light-bulbs-today-compared-to-the-past/ |archive-date=7 March 2017}}</ref> An ideal white light source could produce about 250 lumens per watt, corresponding to a luminous efficiency of 37%.<ref name="max-eff-truncated-1">
{{cite journal|doi=10.1063/1.4721897
| title=Maximum spectral luminous efficacy of white light|journal=Journal of Applied Physics
| volume=111 | issue=10 | year=2012
| last1=Murphy | first1=Thomas W.
| pages=104909–104909–6| article-number=104909| arxiv = 1309.7039
| bibcode = 2012JAP...111j4909M
| s2cid=6543030}}</ref>

For a given quantity of light, an incandescent light bulb consumes more power and emits more heat than most other types of electric light. In buildings where [[air conditioning]] is used, incandescent lamps' heat output increases load on the air conditioning system.<ref>Peter Lund, Helsinki University of Technology, on p. C5 in [[Helsingin Sanomat]] 23 October 2007.</ref> 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.

The chart below lists the luminous efficacy and efficiency for several types of incandescent bulb. A longer chart in [[Luminous efficacy#Overall luminous efficacy|luminous efficacy]] compares a broader array of light sources. 
{| class="wikitable"
|-
!Type||Overall luminous efficiency||Overall luminous efficacy (lm/W)
|-
|40&nbsp;W tungsten incandescent (120 V, general service)
|1.9%
|12.6<ref name="incandescent"/>
|-
|60&nbsp;W tungsten incandescent (120 V, general service)
|2.1%
|14.5<ref name="incandescent"/>
|-
|100&nbsp;W tungsten incandescent (120 V, general service)
|2.6%
|17.5<ref name="incandescent"/>
|-
|Glass halogen
|2.3%
|16
|-
|Quartz halogen
|3.5%
|24
|-
|Photographic and projection lamps with very high filament temperatures and short lifetimes
|5.1%
|35<ref name="bulbguide">{{cite web|author=Klipstein, Donald L. |year=1996 |title=The Great Internet Light Bulb Book, Part I |url=http://freespace.virgin.net/tom.baldwin/bulbguide.html|url-status=dead |archive-url=https://web.archive.org/web/20060502061149/http://freespace.virgin.net/tom.baldwin/bulbguide.html |archive-date=2 May 2006}}</ref>
|-
|Theoretical maximum for a tungsten filament incandescent bulb
|7.6%
|52<ref name="GETP110" />
|}

===Color rendering===
The spectrum of light produced by an incandescent lamp closely approximates that of a [[black body radiator]] at the same temperature.<ref name="Edison_Incandescent">{{cite web|url=http://www.edisontechcenter.org/incandescent.html |title=Incandescent Lamps |work=edisontechcenter.org |url-status=dead |archive-url=https://web.archive.org/web/20130314112308/http://www.edisontechcenter.org/incandescent.html |archive-date=14 March 2013}}</ref> The basis for light sources used as the standard for color perception is a tungsten incandescent lamp operating at a defined temperature.<ref>Janos Schanda (ed), ''Colorimetry: Understanding the CIE System'', John Wiley & Sons, 2007 {{ISBN|0470175621}} page 44</ref>
[[File:Spectral power distribution of a 25 W incandescent light bulb.png|thumb|Spectral power distribution of a 25&nbsp;W incandescent light bulb.]]

Light sources such as fluorescent lamps, [[high-intensity discharge lamp]]s and [[LED lamp]]s have higher luminous efficiency. These devices produce light by [[luminescence]]. 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]]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.<ref>Blain Brown, ''Motion Picture and Video Lighting'', Routledge, 2018, {{ISBN|0429866666}} Chapter 7</ref> [[Metamerism (color)|Metamerism]] describes the effect of different light spectrum distributions on the perception of color.

===Cost of lighting===
{{See also|Architectural lighting design}}
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]] system. During the heating season heat produced by the bulbs is not wasted,<ref>{{cite news | url=https://www.cbc.ca/news/canada/manitoba/efficient-lighting-equals-higher-heat-bills-study-1.856047 | publisher=[[CBC News]] | title=Efficient lighting equals higher heat bills: study | date=4 March 2009 | url-status=live | archive-url=https://web.archive.org/web/20110214132113/https://www.cbc.ca/news/canada/manitoba/efficient-lighting-equals-higher-heat-bills-study-1.856047 | archive-date=14 February 2011}}</ref> 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.<ref name=cmhc>{{cite web |url=http://www.cmhc.ca/odpub/pdf/65830.pdf |title=Benchmarking Home Energy Savings from Energy-Efficient Lighting |date=January 2008 |author=Anil Parekh |publisher=Canada Mortgage and Housing Corporation |access-date=14 January 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160130112609/http://www.cmhc.ca/odpub/pdf/65830.pdf |archive-date=30 January 2016}}</ref>

===Measures to ban use===
{{Main|Phase-out of incandescent light bulbs}}
Since incandescent light bulbs use more energy than alternatives such as [[compact fluorescent lamp|CFL]]s and [[LED lamp]]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 {{Euro|5{{nbsp}}billion}} to {{Euro|10{{nbsp}}billion}} to the economy and saves 40&nbsp;TWh of electricity every year, translating in {{CO2}} emission reductions of {{convert|15|e6t|e9lb|abbr=off}}.<ref>Nicholas A. A.Howarth, Jan Rosenow: ''Banning the bulb: Institutional evolution and the phased ban of incandescent lighting in Germany''. In: ''[[Energy Policy (journal)|Energy Policy]]'' 67, (2014), 737–746, {{doi|10.1016/j.enpol.2013.11.060}}.</ref><ref>{{cite web |title=Frequently asked questions about the regulation on ecodesign requirements for non-directional household lamps |url=https://ec.europa.eu/commission/presscorner/detail/en/MEMO_09_113 |website=European Commission - European Commission |access-date=19 August 2022 |language=en}}</ref>

Objections to banning the use of incandescent light bulbs include the higher initial cost of alternatives and lower quality of light of fluorescent lamps.<ref name=NYT>{{Cite news |url=https://www.nytimes.com/2009/07/06/business/energy-environment/06bulbs.html |author=Leora Broydo Vestel |work=The New York Times |title=Incandescent Bulbs Return to the Cutting Edge |date=6 July 2009|url-status=live |archive-url=https://web.archive.org/web/20110512214719/http://www.nytimes.com/2009/07/06/business/energy-environment/06bulbs.html |archive-date=12 May 2011}}</ref> Some people have concerns about the [[Fluorescent lamps and health|health effects]] of fluorescent lamps.<ref name=scenihr2008>{{cite web |url=http://ec.europa.eu/health/ph_risk/committees/04_scenihr/docs/scenihr_o_019.pdf |archive-url=https://web.archive.org/web/20081112081741/http://ec.europa.eu/health/ph_risk/committees/04_scenihr/docs/scenihr_o_019.pdf |archive-date=2008-11-12 |url-status=live|title=Light Sensitivity, Scientific Committee on Emerging and Newly Identified Health Risks|access-date=2009-08-31|publisher=Director-General for Health and Consumers, European Commission|date=2008|pages=26–27}}</ref>

===Efforts to improve efficacy===
[[File:Wolfram-Halogenglühlampe.png|thumb|upright|Xenon [[halogen lamp]] with an E27 base, which can replace a non-halogen bulb]]
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.<ref name=notsodim>{{Cite web|last=Daley |first=Dan |date=27 February 2008 |title=Incandescent's Not-So-Dim Future |url=https://plsn.com/articles/the-biz/incandescents-not-so-dim-future/|url-status=live|work=Projection, Lights & Staging News |volume=09 |issue=1 |page=46 |publisher=Timeless Communications Corp|archive-url=https://web.archive.org/web/20140306230206/http://www.plsn.com/current-issue/31-the-biz/2520-incandescents-not-so-dim-future.html |archive-date=6 March 2014}}</ref><ref>{{cite press release |last=Freeman |first=Kim |date=23 February 2007 |title=GE Announces Advancement in Incandescent Technology; New High-Efficiency Lamps Targeted for Market by 2010 |url=http://www.businesswire.com/portal/site/ge/index.jsp?ndmViewId=news_view&newsId=20070223005120 |publisher=[[Business Wire]] |url-status=dead |archive-url=https://web.archive.org/web/20130516151220/http://www.businesswire.com/portal/site/ge/index.jsp?ndmViewId=news_view&newsId=20070223005120 |archive-date=16 May 2013}}</ref> The HEI program was terminated in 2008 due to slow progress.<ref>{{cite news |last=Hamilton |first=Tyler |title=Why the brightest idea needs tinkering |url=https://www.thestar.com/business/2009/04/22/why_the_brightest_idea_needs_tinkering.html|newspaper=[[Toronto Star]] |date=22 April 2009 |url-status=live |archive-url=https://web.archive.org/web/20130620083715/http://www.thestar.com/business/2009/04/22/why_the_brightest_idea_needs_tinkering.html|archive-date=20 June 2013}}</ref><ref>{{cite news |last=Rahim |first=Saqib |date=28 June 2010 |title=The Incandescent Bulb Heads Offstage After Century-Long Performance |url=https://www.nytimes.com/cwire/2010/06/28/28climatewire-the-incandescent-bulb-heads-offstage-after-c-11795.html |work=The New York Times |url-status=live |archive-url=https://web.archive.org/web/20130518150756/http://www.nytimes.com/cwire/2010/06/28/28climatewire-the-incandescent-bulb-heads-offstage-after-c-11795.html |archive-date=18 May 2013}}</ref>
US Department of Energy research at [[Sandia National Laboratories]] initially indicated the potential for dramatically improved efficiency from a [[photonic lattice]] filament.<ref name=notsodim/> However, later work indicated that initially promising results were in error.<ref>{{cite web |title=Revolutionary tungsten photonic crystal could provide more power for electrical devices |url=https://share.sandia.gov/news/resources/releases/2003/other/planck-lin.html |publisher=[[Sandia National Laboratories]] |date=7 July 2003 |url-status=live |archive-url=https://web.archive.org/web/20130221204348/https://share.sandia.gov/news/resources/releases/2003/other/planck-lin.html |archive-date=21 February 2013}}</ref>

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&nbsp;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.<ref name=NYT/> This concept was pioneered by Duro-Test in 1980 with a commercial product that produced 29.8&nbsp;lm/W.<ref>{{Cite journal |url=http://americanhistory.si.edu/collections/search/object/nmah_995209 |title=Prototype Heat-Mirror Tungsten Lamp |journal=Smithsonian Museum of American History |url-status=live |archive-url=https://web.archive.org/web/20151223061442/http://americanhistory.si.edu/collections/search/object/nmah_995209 |archive-date=23 December 2015}}</ref><ref>{{cite report|title=Energy Efficient Incandescent Lamp: Final Report |publisher=Lawrence Berkeley National Laboratory |date=April 1982}}</ref> More advanced reflectors based on [[interference filter]]s or [[photonic crystal]]s can theoretically result in higher efficiency, up to a limit of about 270&nbsp;lm/W (40% of the maximum efficacy possible).<ref name=Ilic>{{cite journal |title=Tailoring high-temperature radiation and the resurrection of the incandescent source |first1=Ognjen |last1=Ilic |journal=Nature Nanotechnology |volume=11 |issue=4 |pages=320–4 |year=2016 |doi=10.1038/nnano.2015.309 |pmid=26751172 |bibcode=2016NatNa..11..320I |hdl=1721.1/109242 |osti=1371442 |url=https://dspace.mit.edu/bitstream/1721.1/109242/1/Chen_Tailoring%20high-temperature.pdf |hdl-access=free |access-date=23 September 2019 |archive-date=14 February 2022 |archive-url=https://web.archive.org/web/20220214220607/https://dspace.mit.edu/bitstream/handle/1721.1/109242/Chen_Tailoring |url-status=live }}</ref> Laboratory proof-of-concept experiments have produced as much as 45&nbsp;lm/W, approaching the efficacy of compact fluorescent bulbs.<ref name=Ilic/><ref>{{cite news |last=McGrath |first=Matt |date=12 January 2016 |url=https://www.bbc.com/news/science-environment-35284112 |title=New development could lead to more effective lightbulbs |work=BBC News |url-status=live |archive-url=https://web.archive.org/web/20160113031746/http://www.bbc.com/news/science-environment-35284112 |archive-date=13 January 2016}}</ref>

==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 {{convert|2000|to|3300|K|°C °F}}, well below tungsten's melting point of {{convert|3695|K|°C °F}}. Filament temperatures depend on the filament type, shape, size, and amount of current drawn. The heated filament emits light that approximates a [[black body|continuous spectrum]]. 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]] 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]] lights and other decorative lighting. These are created by [[Glass coloring and color marking|coloring the glass]] with a [[dopant]]; which is often a metal like [[cobalt]] (blue) or [[chromium]] (green).<ref>{{cite web|url=http://www.geconsumerandindustrial.com/environmentalinfo/documents/msds/msds_incandescent_lamps.pdf|title=Lamp Material Information Sheet – Incandescent Lamp|access-date=20 May 2013|url-status=usurped|archive-url=https://web.archive.org/web/20130521005210/http://www.geconsumerandindustrial.com/environmentalinfo/documents/msds/msds_incandescent_lamps.pdf|archive-date=21 May 2013}}</ref> Neodymium-containing glass is sometimes used to provide a more natural-appearing light.

{| border="0"
|
[[File:Incandescent light bulb.svg|frameless|upright=1.25|center]]
|
#Outline of Glass bulb
#Low pressure inert gas ([[argon]], [[nitrogen]], [[krypton]], [[xenon]])
#[[Tungsten]] filament
#Contact wire (goes into stem)
#Contact wire (goes out of stem)
#Support wires (one end embedded in stem; conduct no current)
#Stem (glass mount)
#Contact wire (goes out of stem)
#Cap (sleeve)
#Insulation ([[vitrite]])
#Electrical contact
|}

The glass bulb of a general service lamp can reach temperatures between {{convert|200|and|260|°C|°F}}. Lamps intended for high power operation or used for heating purposes will have envelopes made of hard glass or [[fused quartz]].<ref name="GETP110" />

If a light bulb envelope leaks, the hot tungsten filament reacts with air, yielding an aerosol of brown [[tungsten nitride]], brown [[tungsten dioxide]], violet-blue [[tungsten pentoxide]], 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 {{convert|70|kPa|atm|abbr=on|1}}.<ref name="argon1">{{cite web |url=http://www.uigi.com/argon.html |title=Argon (Ar) Properties, Uses, Applications Argon Gas and Liquid Argon |website=Gas Properties, Uses, Applications |publisher=Universal Industrial Gases, Inc. |archive-url=https://web.archive.org/web/20120204105153/http://www.uigi.com/argon.html |archive-date=4 February 2012 }}</ref>

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 [[Relative atomic mass|atomic]] or [[Molecular mass|molecular weight]] is desirable. The presence of gas keeps the tungsten below its vapor pressure, 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]].

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:<ref name="ChemArtLight">{{cite book|isbn=978-0080933153|url=https://books.google.com/books?id=eaj8BAAAQBAJ&pg=PA263|title=The Chemistry of Artificial Lighting Devices|publisher=Elsevier Science|last=Ropp|first=Richard C.|date = 22 October 2013|url-status=live|archive-url=https://web.archive.org/web/20171206142310/https://books.google.com/books?id=eaj8BAAAQBAJ&pg=PA263&dq=tungsten+wire+drawing&hl=en&sa=X&ei=zzfRVI-9F4HqUOX7gfgJ&ved=0CE0Q6AEwBQ#v=onepage&q=tungsten%20wire%20drawing&f=false|archive-date=6 December 2017}}</ref>

* [[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]] (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<ref name="argon1"/>
* 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]], [[nitrogen]], or [[Mercury (element)|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 ==
[[File:Tantalum light bulb.png|thumb|upright|The 1902 [[tantalum]] filament light bulb was the first one to have a metal filament. This one is from 1908.]]
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.<ref name=":0">{{Cite book |title=Corning and the craft of innovation |last1=Graham |first1=Margaret B. W. |date=2001 |publisher=Oxford University Press |last2=Shuldiner |first2=Alec T. |isbn=0195140974 |location=Oxford [England] |pages=[https://archive.org/details/corningcraftof00grah/page/85 85–95] |oclc=45493270 |url=https://archive.org/details/corningcraftof00grah/page/85 }}</ref> Around 150 bulbs per hour were produced by the hand-blowing process in the 1880s at Corning Glass Works.<ref name=":0" />

The Westlake machine, developed by [[Libbey Glass]], was based on an adaptation of the Owens-Libbey bottle-blowing machine. [[Corning Glass Works]] soon began developing competing automated bulb-blowing machines, the first of which to be used in production was the E-Machine.<ref name=":0" />

=== Ribbon machine ===
Corning continued developing automated bulb-production machines, installing the Ribbon Machine in 1926 in its [[Wellsboro, Pennsylvania|Wellsboro]], Pennsylvania, factory.<ref>{{Cite book |title=Innovations in glass |date=1999 |publisher=Corning Museum of Glass |isbn=0872901467 |location=Corning, New York |page=[https://archive.org/details/innovationsingla0000corn/page/52 52] |oclc=42012660 |url=https://archive.org/details/innovationsingla0000corn/page/52 }}</ref> 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.<ref name=":0" />

The Ribbon Machine works by passing a continuous ribbon of glass 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 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.<ref>{{cite web |url=http://www.enotes.com/how-products-encyclopedia/light-bulb |title=Light Bulb: How Products are Made |archive-url=https://web.archive.org/web/20100914105212/http://www.enotes.com/how-products-encyclopedia/light-bulb |archive-date=14 September 2010}}</ref><ref>{{Cite news|url=https://blog.cmog.org/2018/01/09/running-the-ribbon-machine-stories-from-the-team/|title=Running the ribbon machine: Stories from the team|date=9 January 2018|work=Behind the Glass|access-date=14 May 2018|language=en-US|archive-date=8 February 2019|archive-url=https://web.archive.org/web/20190208214828/https://blog.cmog.org/2018/01/09/running-the-ribbon-machine-stories-from-the-team/|url-status=live}}</ref> By the 1970s, 15 ribbon machines installed in factories around the world produced the entire supply of incandescent bulbs.<ref name=":1">{{Cite news|url=https://blog.cmog.org/2017/01/27/the-machine-that-lit-up-the-world/|title=The machine that lit up the world|date=27 January 2017|work=Behind the Glass|access-date=14 May 2018|language=en-US|archive-date=1 January 2018|archive-url=https://web.archive.org/web/20180101140303/https://blog.cmog.org/2017/01/27/the-machine-that-lit-up-the-world/|url-status=live}}</ref> 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|Osram-Sylvania]]'s Wellsboro, Pennsylvania plant meant that one of the last remaining ribbon machines in the United States was shut down.<ref name=":1" />

==Filament==
[[File:Light-Bulb-Filament-engineerguy.ogv|thumb|left|How a tungsten filament is made]]

[[Carbon]] has the highest melting point of any element, and in [[carbon arc lamp]]s it had been demonstrated to produce incandescence fairly close to that of sunlight. However, carbon has a tendency to [[Sublimation (phase transition)|sublimate]] before reaching its melting point depending on pressure, which led to rapid blackening of vacuumed bulbs. The first commercially successful light bulb filaments were made from carbonized paper or [[bamboo]]. Carbon filaments have a negative [[Temperature coefficient of resistivity|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 (electrical)|conductor]], which stabilized the lamps operating properties against minor variations in supply voltage.

Metal filaments were tried in 1897<ref>{{cite web | url=https://www.refractorymetal.org/tungsten-wire-history | title=Tungsten Wire History | date=4 December 2020 | access-date=1 January 2023 | archive-date=1 January 2023 | archive-url=https://web.archive.org/web/20230101152531/https://www.refractorymetal.org/tungsten-wire-history/ | url-status=dead }}</ref> and started to displace carbon starting around 1904. Tungsten has the highest available melting point, but brittleness was a big obstacle. 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 (so-called AKS tungsten) greatly improved the life and durability of the tungsten filaments.<ref name=tungstendoping>Chapter 2 ''The Potassium Secret Behind Tungsten Wire Production''</ref>

The predominant mechanism for failure in tungsten filaments even now is [[grain boundary sliding]] accommodated by diffusional creep.<ref name=":4">{{Cite journal|last1=Raj|first1=R.|last2=King|first2=G. W.|date=1978-07-01|title=Life Prediction of Tungsten Filaments in Incandescent Lamps|url=https://doi.org/10.1007/BF02649838|journal=Metallurgical Transactions A|language=en|volume=9|issue=7|pages=941–946|doi=10.1007/BF02649838|bibcode=1978MTA.....9..941R |s2cid=135784495 |issn=1543-1940|url-access=subscription}}</ref> During operation, the tungsten wire is stressed under the load of its own weight and because of the diffusion that can occur at high temperatures, grains begin to rotate and slide. This stress, because of variations in the filament, causes the filament to sag nonuniformly, which ultimately introduces further torque on the filament.<ref name=":4" /> It is this sagging that inevitably results in a rupture of the filament, rendering the incandescent lightbulb useless.<ref name=":4" />

===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 {{convert|22.8|in|order=flip}},<ref name="GETP110" /> and the filament diameter is {{convert|0.0018|in|order=flip}}. 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.<ref>Donald G. Fink, H. Wayne Beatty, ''Standard Handbook for Electrical Engineers, Eleventh Edition'', McGraw Hill, 1978 {{ISBN|0-07-020974-X}}, page 22-5</ref>

{{stack|
[[File:filament.jpg|thumb|Coiled coil filament of a 200-watt incandescent lightbulb highly magnified]]
[[File:Fused Electrical Filament SEM Stereo 50x.JPG|thumb|Filament of a burnt-out 50-watt incandescent lightbulb in an [[Scanning electron microscope|SEM]] in stereoscopic mode, presented as an [[anaglyph image]].{{3D glasses}}]]
[[File:Fused Electrical Filament SEM Stereo 500x.JPG|thumb|Filament of a 50-watt incandescent lightbulb in an [[Scanning electron microscope|SEM]] in stereoscopic mode, presented as an [[anaglyph image]].{{3D glasses}}]]
}}

Electrical filaments are also used in [[hot cathode]]s of [[fluorescent lamp]]s and [[vacuum tube]]s as a source of [[electron]]s 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.<ref name="StdHdbk11"/> 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 compact fluorescent 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]] and some [[nitrogen]],<ref name="IES1981">John Kaufman (ed.), ''IES Lighting Handbook 1981 Reference Volume'', Illuminating Engineering Society of North America, New York, 1981 {{ISBN|0-87995-007-2}} page 8-6</ref> or sometimes [[krypton]].<ref>Burgin. Lighting Research and Technology 1984 16.2 61–72</ref> 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.<ref>{{cite web|url=http://donklipstein.com/xeincand.html#p|title=Premium Fill Gasses|last=Lipstein|first=Don|access-date=13 October 2011|url-status=live|archive-url=https://web.archive.org/web/20111011122615/http://donklipstein.com/xeincand.html#p|archive-date=11 October 2011}}</ref>

''Filament notching'' is due to uneven evaporation of the filament. Small variations in [[electrical resistivity|resistivity]] along the filament cause "hot spots" to form at points of higher resistivity;<ref name="Kane2001"/> a variation of diameter of only 1% will cause a 25% reduction in service life.<ref name="GETP110" /> 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]] can be used to counteract the effect.<ref>{{cite web |title=Miniature Lamps: Technical Information |publisher=Toshiba Lighting & Technology Corporation |url=https://www.tlt.co.jp/tlt/english/products/industrial_light/miniature_lamp/catalog/info.htm |access-date=25 February 2019 |archive-date=26 February 2019 |archive-url=https://web.archive.org/web/20190226112649/https://www.tlt.co.jp/tlt/english/products/industrial_light/miniature_lamp/catalog/info.htm |url-status=live }}</ref><ref>John Kaufman (ed.), ''IES Lighting Handbook 1981 Reference Volume'', Illuminating Engineering Society of North America, New York, 1981 {{ISBN|0-87995-007-2}} page 8-9</ref>

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 [[fuse (electrical)|fuses]] built into the light bulb.<ref>{{cite web|url=http://www.teralab.co.uk/Glass_Blowing/Lamp_Autopsy/Lamp_Autopsy_Page1.htm|title=Glass Blowing for Vacuum Devices – Lamp Autopsy|last=Hunt|first=Robert|date=2001–2006|publisher=Teralab|access-date=2 May 2007|url-status=live|archive-url=https://web.archive.org/web/20070311121008/http://www.teralab.co.uk/Glass_Blowing/Lamp_Autopsy/Lamp_Autopsy_Page1.htm|archive-date=11 March 2007}}</ref> More nitrogen is used in higher-voltage lamps to reduce the possibility of arcing.<ref name="IES1981"/>

===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.<ref>IEC 60064 Tungsten filament lamps for domestic and similar general lighting purposes.</ref> Study of the problem of bulb blackening led to the discovery of [[thermionic emission]], the invention of the [[vacuum tube]], and [[Evaporation (deposition)|evaporation deposition]] used to make [[mirror]]s and other [[Thin-film optics|optical coatings]].<ref>{{cite journal |first=William Henry |last=Preece |author-link=William Preece |year=1885 |url=https://books.google.com/books?id=xmdDAAAAYAAJ&pg=PA219 |title=On a peculiar behaviour of glow lamps when raised to high incandescence |journal=Proceedings of the Royal Society of London |volume=38 |issue= 235–238|pages=219–230 |doi=10.1098/rspl.1884.0093 |url-status=live |archive-url=https://web.archive.org/web/20140626213555/http://books.google.com/books?id=xmdDAAAAYAAJ&pg=PA219 |archive-date=26 June 2014 |doi-access=free }} Preece coins the term the "Edison effect" on page 229.</ref><ref name=Josephson>
{{cite book
 |last1=Josephson |first1=M.
 |year=1959
 |title=Edison
 |url=https://archive.org/details/edisonbiography00jose |url-access=registration |publisher=[[McGraw-Hill]]
 |isbn=978-0-07-033046-7
}}</ref><ref>''The Foundations of Vacuum Coating Technology'' By D. M. Mattox &ndash; Springer 2004 Page 37</ref>

A very small amount of water vapor inside a light bulb can significantly increase lamp darkening. Water vapor [[thermolysis|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''.<ref name="Kane2001"/> The equivalent of a drop of water distributed over 500,000 lamps will significantly increase darkening.<ref name="GETP110"/> Small amounts of substances such as [[zirconium]] are placed within the lamp as a [[getter]] to react with any oxygen that may bake out of the lamp components during operation.<ref>Corazza, Alessio & Giorgi, S. & Boffito, Claudio & Massaro, Vincenzo & Caccia, Debora. (2006). Characteristics of the getter materials used in High Intensity Discharge Lamps. Conference Record - IAS Annual Meeting (IEEE Industry Applications Society). 4. 1801-1807. 10.1109/IAS.2006.256780.</ref>

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.<ref>John Kaufman (ed.), ''IES Lighting Handbook 1981 Reference Volume'', Illuminating Engineering Society of North America, New York, 1981 {{ISBN|0-87995-007-2}} page 8-10</ref>

===Halogen lamps===
{{Main|Halogen lamp}}
[[File:Tungsten filament in halogen lamp.JPG|thumb|Close-up of a tungsten filament inside a [[halogen lamp]]. The two ring-shaped structures left and right are filament supports.]]

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]] 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. [[Optical fiber|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 [[microscope]]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]] but were easier to operate. Developed around 1915, these lamps were displaced by mercury and [[xenon arc lamp]]s.<ref>{{cite web|title=Incandescent Arc Lamps|url=http://www.lamptech.co.uk/Miscellaneous.htm|publisher=Museum of Electric Lamp Technology|year=2004|url-status=live|archive-url=https://web.archive.org/web/20130801233142/http://lamptech.co.uk/Miscellaneous.htm|archive-date=1 August 2013}}</ref><ref>G. Arncliffe Percival, ''The Electric Lamp Industry'', Sir Isaac Pitman and Sons, Ltd. London, 1920 pp. 73–74, available from the [[Internet Archive]]</ref><ref>S. G. Starling, ''An Introduction to Technical Electricity'', McMillan and Co., Ltd., London 1920, pp. 97–98, available at the [[Internet Archive]], good schematic diagram of the Pointolite lamp</ref>

==Electrical characteristics==
{| class="wikitable" |
|+ Comparison of efficacy by power
!
! colspan="2" | 120-volt lamps<ref name=Wells2012>{{Citation
 | title = Smart Grid Home
 | url = https://books.google.com/books?id=-ILFECcjG-gC&q=120+volt+incandescent+efficacy+chart&pg=PA163
 | year = 2012
 | author = Wells, Quentin
 | isbn = 978-1111318512
 | page = 163
 | publisher=Cengage Learning | access-date = 8 November 2012
| archive-date = 17 August 2021
| archive-url = https://web.archive.org/web/20210817015815/https://books.google.com/books?id=-ILFECcjG-gC&q=120+volt+incandescent+efficacy+chart&pg=PA163
 | url-status = live
 }}</ref>
! colspan="2" | 230-volt lamps<ref>{{cite book | last=Häberle | first=Gregor D.|display-authors=etal| title=Tabellenbuch Elektrotechnik|edition=25| publisher=[[Verlag Europa-Lehrmittel]]| publication-place=Haan-Gruiten | year=2013 | isbn=978-3-8085-3227-0 | language=de | page=190}}</ref>
|-
!Power (W)!!Output ([[lumen (unit)|lm]])!!Efficacy (lm/W)!!Output ([[lumen (unit)|lm]])!!Efficacy (lm/W)
|-
|5  ||  25 ||5   || ||
|-
|15 ||  110||7.3 || ||
|-
|25 ||  200||8.0 ||230||9.2
|-
|40 ||  500||12.5||430||10.8
|-
|60 ||  850||14.2||730||12.2
|-
|75 ||1,200||16.0|| ||
|-
|100||1,700||17.0||1,380||13.8
|-
|150||2,850||19.0||2,220||14.8
|-
|200||3,900||19.5||3,150||15.8
|-
|300||6,200||20.7||5,000||16.7
|-
|500||     ||    ||8,400||16.8
|}

===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]] in the circuit. Incandescent light bulbs are usually [[marketing|marketed]] according to the [[electric power|electrical power]] consumed. This depends mainly on the operating [[electrical resistance|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 [[Lumen (unit)|lumens]], of standard 120 volt incandescent light bulbs at various powers. Light output of similar 230&nbsp;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 [[Efficient energy use|energy efficiency]].<ref>{{cite web|url=http://donklipstein.com/lfunfact.html|title=Light and Lighting Fun Facts|work=donklipstein.com|url-status=live|archive-url=https://web.archive.org/web/20130720233038/http://donklipstein.com/lfunfact.html|archive-date=20 July 2013}}</ref> 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 {{frac|1|15}} the resistance when operating. For example, a 100-watt, 120-volt lamp has a resistance of 144&nbsp;[[ohm]]s when lit, but the cold resistance is much lower (about 9.5&nbsp;ohms).<ref name="GETP110" />{{efn|1=Edison's research team was aware of the large negative [[temperature coefficient of resistance]] of possible lamp filament materials and worked extensively during the period 1878–1879 on devising an automatic regulator or ''ballast'' to stabilize current. It was not until 1879 that it was realized a self-limiting lamp could be built.<ref name="fris10">{{cite book |last1=Friedel |first1=Robert |last2=Israel |first2=Paul |year=2010 |name-list-style=amp |title=Edison's Electric Light: The Art of Invention |publisher=The Johns Hopkins University Press |edition=Revised |isbn=978-0-8018-9482-4 |pages=29–31}}</ref>}} Since incandescent lamps are resistive loads, simple phase-control [[TRIAC]] [[dimmer]]s 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.{{sfnp|Friedel|Israel|2010|pp=[https://books.google.com/books?id=8U-Naf4DuzMC&pg=PA22 22–23]}}

==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 (electrical)|fuse]]: if a broken filament produces an [[electrical short]] 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 [[implosion (mechanical process)|implodes]], exposing the filament to ambient air. The air then usually destroys the hot filament through [[oxidation]].

===Bulb shapes ===
[[File:incandescent bulb shapes.svg|thumb|upright=2|Incandescent light bulbs come in a range of shapes and sizes.]]
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]] C79.1-2002, [[Indian Standard|IS]] 14897:2000<ref name="IS 14897:2000">{{cite web |title=IS 14897 (2000): Glass Bulb Designation System for Lamps — Guide |publisher=Bureau of Indian Standards |location=New Delhi |url=https://archive.org/details/gov.in.is.14897.2000 |access-date=3 July 2018 |pages=1, 4 }}</ref> and [[Japanese Industrial Standards|JIS]] C 7710:1988<ref name="JIS C 7710:1988">{{cite web |script-title=ja:JIS C 7710:1988 電球類ガラス管球の形式の表し方|url=http://kikakurui.com/c7/C7710-1988-01.html |access-date=21 March 2017 |language=ja |url-status=live |archive-url=https://web.archive.org/web/20161111224419/http://kikakurui.com/c7/C7710-1988-01.html |archive-date=11 November 2016}}</ref> cover a common terminology for bulb shapes.

{| class="wikitable"
|+ Examples
|-
! Description !! SI !! Inch !! Details
|-
| "Standard" lightbulb || A60 E26 || A19 E26 || [[⌀]]60&nbsp;mm (~⌀19/8&nbsp;in) [[A-series light bulb|A series bulb]], ⌀26&nbsp;mm [[Edison screw]]
|-
| Candle-flame bulb || CA35 E12 || CA11 E12 || ⌀35&nbsp;mm (~⌀11/8&nbsp;in) candle-flame shape, ⌀12&nbsp;mm Edison screw
|-
| Flood light || BR95 E26 || BR30 E26 || ⌀95&nbsp;mm (~⌀30/8&nbsp;in) flood light, ⌀26&nbsp;mm Edison screw
|-
| Halogen track-light bulb || MR50 GU5.3 || MR16 GU5.3 || ⌀50&nbsp;mm (~⌀16/8&nbsp;in) [[multifaceted reflector]], 5.33&nbsp;mm-spaced 12&nbsp;V [[bi-pin connector]]
|}

=== Common shape codes ===

;General Service/General Lighting Service (GLS)
:Light emitted in (nearly) all directions. Available either clear or frosted.
:Types: [[A-series light bulb|General]] (A), elliptical (E), mushroom (M), sign (S), tubular (T)
:120&nbsp;V sizes: A17, 19 and 21
:230&nbsp;V sizes: A55 and 60{{efn|name=EU-metric|1=Size measured in millimetres. See also [[A-series light bulb]].}}

;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&nbsp;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&nbsp;V sizes: R16, 20, 25 and 30
:230&nbsp;V sizes: R50, 63, 80 and 95{{efn|name=EU-metric}}

;Parabolic aluminized reflector (PAR)
:[[Parabolic aluminized reflector light|Parabolic aluminized reflector]] (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&nbsp;V sizes: PAR 16, 20, 30, 38, 56 and 64
:230&nbsp;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 {{frac|1|8}} of an inch. Therefore, a PAR 16 is {{cvt|2|in|order=flip}} in diameter, a PAR 20 is {{cvt|2.5|in|order=flip}} in diameter, PAR 30 is {{cvt|3.75|in|order=flip}} and a PAR 38 is {{cvt|4.75|in|order=flip}} in diameter.
[[File:GE 60 watt package light bulbs.jpg|thumb|A package of four 60-watt light bulbs]]

;Multifaceted reflector (MR)
:[[Multifaceted reflector]] bulbs are usually smaller in size and run at a lower voltage, often 12&nbsp;V.

[[File:MR-Variations.jpg|thumb|Left to right: MR16 with GU10 base, MR16 with GU5.3 base, MR11 with GU4 or GZ4 base]]

;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.<ref>{{cite web |url=http://www.gelighting.com/na/business_lighting/education_resources/glossary.htm |title=Lighting Resources |work=GE Lighting North America |url-status=dead |archive-url=https://web.archive.org/web/20070703041351/http://www.gelighting.com/na/business_lighting/education_resources/glossary.htm |archive-date=3 July 2007 }}</ref> The [[Osram]] designation for a similar coating is "IRC".<ref>{{cite web |url=http://www.osram.com/osram_com/Tools_%26_Services/Calculators_and_Consultants/IRC_Saver_calculator/index.html |publisher=Osram |title=IRC Saver calculator |url-status=dead |archive-url=https://web.archive.org/web/20081223121730/http://www.osram.com/osram_com/Tools_%26_Services/Calculators_and_Consultants/IRC_Saver_calculator/index.html |archive-date=23 December 2008 }}</ref>

===Lamp bases===
{{Main|Lightbulb socket}}
[[File:Gloedelampe fatninger.jpg|right|thumb|40-watt light bulbs with standard E10, E14 and E27 Edison screw base]]
[[File:Light bulb with bayonet base.JPG|thumb|The double-contact bayonet cap on an incandescent bulb]]
Large lamps may have a [[Edison screw|screw base]] or a [[Bayonet mount|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 lamp types|automotive lamps]] to resist loosening by vibration. 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. Very small lamps may have the filament support wires extended through the base of the lamp for connections. A [[bipin]] base is often used for halogen or reflector lamps.<ref>{{cite web |title=Single-Ended Halogen Bases |url=http://www.bulbster.com/lightbulbs/singleended-halogen-c-783_43230.html |publisher=Bulbster.com |access-date=17 June 2013 |url-status=live |archive-url=https://web.archive.org/web/20130919152653/http://bulbster.com/lightbulbs/singleended-halogen-c-783_43230.html |archive-date=19 September 2013}}</ref>

In the late 19th century, manufacturers introduced a multitude of incompatible lamp bases. [[General Electric]]'s "[[Mazda (light bulb)|Mazda]]" 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]] 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==
{{See also|Lamp rerating}}
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''<sup> 3.4</sup>
* ''Power'' consumption is approximately proportional to ''V''<sup> 1.6</sup>
* ''Lifetime'' is approximately proportional to ''V''<sup> −16</sup>
* ''Color temperature'' is approximately proportional to ''V''<sup> 0.42</sup><ref name="StdHdbk11">[[Donald G. Fink]] and H. Wayne Beaty, ''Standard Handbook for Electrical Engineers, Eleventh Edition'', McGraw-Hill, New York, 1978, {{ISBN|0-07-020974-X}}, pg 22–8</ref>

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.<ref name="GETP110" /> Early bulbs had a life of up to 2500 hours, but in 1924 the [[Phoebus cartel]] agreed to limit life to 1000 hours.<ref>{{cite web |title=The Great Lightbulb Conspiracy |url=https://spectrum.ieee.org/the-great-lightbulb-conspiracy |work=IEEE Spectrum |publisher=IEEE |first=Markus |last=Krajewski |date=24 September 2014|url-status=live |archive-url=https://web.archive.org/web/20141106040631/https://spectrum.ieee.org/geek-life/history/the-great-lightbulb-conspiracy |archive-date=6 November 2014}}</ref> When this was exposed in 1953, General Electric and other leading American manufacturers were banned from limiting the life.<ref>{{cite web|url=http://www.mercurynews.com/ci_17287091|title=Tests shine light on the secret of the Livermore light bulb|date=6 February 2011|url-status=live|archive-url=https://web.archive.org/web/20120310100846/http://www.mercurynews.com//ci_17287091|archive-date=10 March 2012}}</ref>

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]]" is a light bulb that is accepted by the ''[[Guinness Book of World Records]]'' as having been burning almost continuously at a [[fire station]] in [[Livermore, California]], 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.<ref>{{cite web|url=http://www.homelighting.com/article.cfm?intarticleID=880 |title=Watts Up? – A parting look at lighting|archive-url=https://web.archive.org/web/20090207211654/http://www.homelighting.com/article.cfm?intarticleID=880 |archive-date=7 February 2009}}</ref>

[[Photoflood|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, {{convert|3695|K|°C °F}}. A 50-hour-life projection bulb, for instance, is designed to operate only {{convert|50|°C|°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.<ref name="GETP110" />

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&nbsp;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.<ref name="GETP110" /> 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.<ref name="GETP110" /> Some infrared heating elements are made for higher voltages, but these use tubular bulbs with widely separated terminals.

<gallery widths="200" heights="200">
File:Livermore Centennial Light Bulb.jpg|The [[Centennial Light]] 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.
</gallery>

==See also==
{{Portal|Energy|Physics}}
* [[3-way lamp]]
* [[Flash (photography)]]
* [[Lampshade]]
* [[Light tube]]
* [[Lightbulb joke]]s
* [[List of light sources]]
* [[Longest-lasting light bulbs]]
* [[Light pollution]]
* [[Photometry (optics)]]
* [[Resistance wire]]
* [[Spectrometer]]

== Explanatory notes ==
{{notelist|45em}}

==References==
{{reflist|30em}}

==External links==
{{Commons category|Incandescent light bulbs}}
* [https://www.graphics.cornell.edu/online/measurements/source-spectra/index.html Light Source Spectra] 60&nbsp;W-100&nbsp;W Incandescent light bulb spectra, from Cornell University Program of Computer Graphics
* [https://www.youtube.com/watch?v=ZlmMaJB7Rmc Slow-motion video of an incandescent lightbulb filament]
* [https://www.youtube.com/watch?v=fpendktZPbE Ribbon machine in operation at Osram-Sylvania in 2016]

{{Artificial light sources}}
{{Thomas Edison}}
{{Technology topics}}
{{Authority control}}

[[Category:Incandescent light bulbs| ]]
[[Category:1878 introductions]]
[[Category:19th-century inventions]]
[[Category:Articles containing video clips]]
[[Category:Discovery and invention controversies]]
[[Category:English inventions]]
[[Category:Thomas Edison]]