Editing Electric light (section)

== Types ==
=== Incandescent ===
{{Main|Incandescent light bulb}}
[[File:This room is equipped with Edison electric light.jpg|thumb|Sign with instructions on the use of light bulbs]]
[[File:Hagley, St John the Baptist - interior, Mason memorial.jpg|thumb|A tablet at [[Hagley#Churches|St John the Baptist Church, Hagley]] commemorates the installation of electric light in 1934.]]
In its modern form, the incandescent light bulb consists of a coiled filament of [[tungsten]] sealed in a globular glass chamber, either a vacuum or full of an [[noble gas|inert gas]] such as [[argon]]. When an electric current is connected, the tungsten is heated to {{convert|2,000 to 3,300|K|°C °F}} and glows, emitting light that approximates a [[continuous spectrum]].

Incandescent bulbs are highly inefficient, in that just 2–5% of the energy consumed is emitted as [[visible light spectrum|visible, usable light]]. The remaining 95% is lost as [[heat]].<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 |archive-date=19 August 2022 |archive-url=https://web.archive.org/web/20220819185359/https://tlo.mit.edu/technologies/high-efficiency-incandescent-lighting |url-status=live }}</ref> In warmer climates, the emitted heat must then be removed, putting additional pressure on [[Ventilation (architecture)|ventilation]] or [[air conditioning]] systems.<ref>{{cite web |title=6 Ways to Save Money on Your Air Conditioning Bill |url=https://www.nopec.org/blognewsroom/blog/6-ways-to-save-money-on-your-air-conditioning-bill |website=NOPEC |access-date=19 August 2022 |language=en |archive-date=19 August 2022 |archive-url=https://web.archive.org/web/20220819193016/https://www.nopec.org/blognewsroom/blog/6-ways-to-save-money-on-your-air-conditioning-bill |url-status=live }}</ref> In colder weather, the heat byproduct has some value, and has been successfully harnessed for warming in devices such as [[Infrared lamp|heat lamps]]. Incandescent bulbs are nonetheless being [[Phase-out of incandescent light bulbs|phased out]] in favor of technologies like [[Compact fluorescent lamp|CFLs]] and [[LED lamp|LED bulbs]] in many countries due to their low energy efficiency. The [[European Commission]] estimated in 2012 that a complete ban on incandescent bulbs would contribute 5 to 10 billion euros to the economy and save 15 billion metric tonnes of [[carbon dioxide emissions]].<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 |access-date=19 August 2022 |language=en |archive-date=19 August 2022 |archive-url=https://web.archive.org/web/20220819191645/https://ec.europa.eu/commission/presscorner/detail/en/MEMO_09_113 |url-status=live }}</ref>

=== Halogen ===
{{Main|Halogen lamp}}
Halogen lamps are usually much smaller than standard incandescent lamps, because for successful operation a bulb temperature over 200&nbsp;°C is generally necessary. For this reason, most have a bulb of fused silica (quartz) or aluminosilicate glass. This is often sealed inside an additional layer of glass. The outer glass is a safety precaution, to reduce ultraviolet emission and to contain hot glass shards should the inner envelope explode during operation.<ref>{{Cite web |title=Tungsten Halogen – Double Jacket |url=http://www.lamptech.co.uk/TH%20DJ.htm |access-date=2023-03-06 |website=www.lamptech.co.uk}}</ref> Oily residue from [[fingerprint]]s may cause a hot quartz envelope to shatter due to excessive heat buildup at the contamination site.<ref>{{Cite web |title=Should you not touch halogen capsule bulbs with your fingers? |url=https://www.lightingcompany.co.uk/is-it-true-you-should-not-touch-halogen-capsule-bulbs-with-your-fingers-i98 |access-date=2023-03-06 |website=The Lighting Company}}</ref> The risk of burns or fire is also greater with bare bulbs, leading to their prohibition in some places, unless enclosed by the luminaire.

Those designed for 12- or 24-volt operation have compact filaments, useful for good optical control. Also, they have higher efficacies (lumens per watt) and longer lives than non-halogen types. The light output remains almost constant throughout their life.

=== Fluorescent ===
{{Main|Fluorescent lamp}}
[[File:Leuchtstofflampen-chtaube050409.jpg|thumb|Top, two compact fluorescent lamps. Bottom, two fluorescent tube lamps. A matchstick, left, is shown for scale.]]
[[Fluorescent lamp]]s consist of a glass tube that contains mercury vapour or argon under low pressure. Electricity flowing through the tube causes the gases to give off ultraviolet energy. The inside of the tubes are coated with [[phosphor]]s that give off visible light when struck by ultraviolet [[photon]]s.<ref>{{cite book|last1=Perkowitz|first1=Sidney|last2=Henry|first2=A. Joseph|date=23 November 1998|title=Empire of Light:: A History of Discovery in Science and Art|url=https://books.google.com/books?id=ROHJnk2JOfIC&q=fluorescent+lights+mercury+vapor+excites|publisher=Joseph Henry Press|isbn=978-0-309-06556-6|access-date=10 November 2020|archive-date=20 October 2021|archive-url=https://web.archive.org/web/20211020105531/https://books.google.com/books?id=ROHJnk2JOfIC&q=fluorescent+lights+mercury+vapor+excites|url-status=live}}</ref> They have much higher efficiency than incandescent lamps. For the same amount of light generated, they typically use around one-quarter to one-third the power of an incandescent. The typical [[luminous efficacy]] of fluorescent lighting systems is 50–100 lumens per watt, several times the efficacy of incandescent bulbs with comparable light output. Fluorescent lamp fixtures are more costly than incandescent lamps, because they require a [[electrical ballast|ballast]] to regulate the [[Electric current|current]] through the lamp, but the lower energy cost typically offsets the higher initial cost. [[Compact fluorescent lamp]]s are available in the same popular sizes as incandescent lamps and are used as an [[Energy conservation|energy-saving]] alternative in homes. Because they contain mercury, many fluorescent lamps are classified as [[hazardous waste]]. The [[United States Environmental Protection Agency]] recommends that fluorescent lamps be segregated from general waste for [[recycling]] or safe disposal, and some jurisdictions require recycling of them.<ref>{{cite web|url=http://www.epa.gov/waste/hazard/wastetypes/universal/lamps/index.htm|title=Hazardous Waste|author=United States Environmental Protection Agency, OSWER|website=US EPA|access-date=3 November 2018|date=2015-07-23|archive-date=2015-06-29|archive-url=https://web.archive.org/web/20150629230450/http://www.epa.gov/waste/hazard/wastetypes/universal/lamps/index.htm|url-status=live}}</ref>

=== LED ===
{{Main|LED lamp}}
[[File:Led-lampa.jpg|thumb|[[LED lamp]] with E27 [[Edison screw]] base]]
The solid-state [[light-emitting diode]] (LED) has been popular as an indicator light in [[consumer electronics]] and professional audio gear since the 1970s. In the 2000s, efficacy and output have risen to the point where LEDs are now being used in lighting applications such as car headlights<ref name="auto2">{{Cite web |last=Linkov |first=Jon |title=LED Headlights Can Be Brighter but Often Lack Clear Advantages |url=https://www.consumerreports.org/headlights/led-headlights-can-be-brighter-but-often-lack-clear-advantages/ |access-date=2023-03-06 |website=Consumer Reports |date=6 August 2019 |language=en-US}}</ref> and brake lights,<ref name="auto2"/> in flashlights<ref>{{Cite web |title=How to Choose Flashlights {{!}} REI Co-op |url=https://www.rei.com/learn/expert-advice/flashlight.html |access-date=2023-03-06 |website=REI |language=en}}</ref> and bicycle lights,<ref>{{Cite web |date=2022-07-19 |title=See and Be Seen with The 13 Best Bike Lights for Every Kind of Ride |url=https://www.bicycling.com/bikes-gear/a20023360/8-bike-lights-we-love/ |access-date=2023-03-06 |website=Bicycling |language=en-us}}</ref> as well as in decorative applications, such as holiday lighting.<ref name="auto1">{{Cite web |title=LED Lighting |url=https://www.energy.gov/energysaver/led-lighting |access-date=2023-03-06 |website=Energy.gov |language=en}}</ref> Indicator LEDs are known for their extremely long life, up to 100,000 hours, but lighting LEDs are operated much less conservatively, and consequently have shorter lives. LED technology is useful for [[lighting design]]ers, because of its low power consumption, low heat generation, instantaneous on/off control, and in the case of single color LEDs, continuity of color throughout the life of the diode and relatively low cost of manufacture.<ref name="auto1"/> LED lifetime depends strongly on the temperature of the diode.<ref>{{Cite web |last= |first= |date=2022-05-23 |title=The truth about LED lifespan and the longevity of your display |url=https://insights.samsung.com/2022/05/23/the-truth-about-led-lifespan-and-the-longevity-of-your-display/ |access-date=2023-03-06 |website=Samsung Business Insights |language=en-US}}</ref> Operating an LED lamp in conditions that increase the internal temperature can greatly shorten the lamp's life. Some lasers have been adapted as an alternative to LEDs to provide highly focused illumination.<ref>{{cite web | url=https://www.edn.com/laser-diodes-add-intensity-to-narrow-beam-lighting/ | title=Laser diodes add intensity to narrow-beam lighting | date=13 May 2019 }}</ref><ref>{{cite web | url=https://www.laserfocusworld.com/lasers-sources/article/16548296/laser-lighting-white-light-lasers-challenge-leds-in-directional-lighting-applications | title=Laser Lighting: White-light lasers challenge LEDs in directional lighting applications | date=22 February 2017 }}</ref>

=== Carbon arc ===
{{Main|Arc lamp}}
[[File:Xenon short arc 1.jpg|thumb|The 15 kW [[Xenon arc lamp|xenon short-arc lamp]] used in the [[IMAX]] projection system.]]
[[File:Microscope MercuryArcBulb Detail.jpg|thumb|right|A [[mercury (element)|mercury]] arc lamp from a [[fluorescence microscope]].]]
Carbon arc lamps consist of two carbon rod [[electrode]]s in open air, supplied by a current-limiting [[Electrical ballast|ballast]]. The [[electric arc]] is struck by touching the rod tips then separating them. The ensuing arc produces a white-hot [[Plasma (physics)|plasma]] between the rod tips. These lamps have higher efficacy than filament lamps, but the carbon rods are short-lived and require constant adjustment in use, as the intense heat of the arc erodes them.<ref name=edison >{{Cite web|url=http://www.edisontechcenter.org/ArcLamps.html |title=Arc Lamps – How They Work & History |last=Center|first=Edison Tech |website=www.edisontechcenter.org|access-date=2018-01-13|url-status = live|archive-url=https://web.archive.org/web/20170617231552/http://www.edisontechcenter.org/ArcLamps.html |archive-date=2017-06-17}}</ref> The lamps produce significant [[ultraviolet]] output, they require ventilation when used indoors, and due to their intensity they need protection from direct sight.

Invented by [[Humphry Davy]] around 1805, the carbon arc was the first practical electric light.<ref name="Whelan">{{cite web |last=Whelan |first=M. |date=2013 |title=Arc Lamps |url=http://www.edisontechcenter.org/ArcLamps.html |url-status=live |archive-url=https://web.archive.org/web/20141110140158/http://www.edisontechcenter.org/ArcLamps.html |archive-date=November 10, 2014 |access-date=November 22, 2014 |work=Resources |publisher=[[Edison Tech Center]]}}</ref><ref name="Sussman">{{cite book |last1=Sussman |first1=Herbert L. |url=https://books.google.com/books?id=sTbPkEXsA5QC&dq=%22arc+lamp%22&pg=PA124 |title=Victorian Technology: Invention, Innovation, and the Rise of the Machine |date=2009 |publisher=ABC-CLIO |isbn=978-0275991692 |pages=124 |doi= |id=}}</ref> It was used commercially beginning in the 1870s for large building and street lighting until it was superseded in the early 20th century by the incandescent light.<ref name="Whelan" /> Carbon arc lamps operate at high power and produce high intensity white light. They also are a point source of light. They remained in use in limited applications that required these properties, such as [[movie projector]]s, [[stage lighting]], and [[searchlight]]s, until after World War II.<ref name=edison />

=== Discharge ===
{{Main|Gas-discharge lamp}}
A discharge lamp has a glass or silica envelope containing two metal [[electrode]]s separated by a gas. Gases used include, [[neon]], [[argon]], [[xenon]], [[sodium]], [[metal halides]], and [[Mercury (element)|mercury]]. The core operating principle is much the same as the carbon arc lamp, but the term "arc lamp" normally refers to carbon arc lamps, with more modern types of gas discharge lamp normally called discharge lamps. With some discharge lamps, very high voltage is used to strike the arc. This requires an electrical circuit called an igniter, which is part of the [[electrical ballast]] circuitry. After the arc is struck, the internal resistance of the lamp drops to a low level, and the ballast limits the current to the operating current. Without a ballast, excess current would flow, causing rapid destruction of the lamp.

Some lamp types contain a small amount of neon, which permits striking at normal running voltage with no external ignition circuitry. [[Sodium-vapor lamp|Low-pressure sodium lamps]] operate this way. The simplest ballasts are just an inductor, and are chosen where cost is the deciding factor, such as street lighting. More advanced electronic ballasts may be designed to maintain constant light output over the life of the lamp, may drive the lamp with a square wave to maintain completely flicker-free output, and shut down in the event of certain faults.

The most efficient source of electric light is the low-pressure sodium lamp. It produces, for all practical purposes, a [[monochromatic light|monochromatic]] orange-yellow light, which gives a similarly monochromatic perception of any illuminated scene. For this reason, it is generally reserved for outdoor public lighting applications. Low-pressure sodium lights are favoured for public lighting by astronomers, since the [[light pollution]] that they generate can be easily filtered, contrary to broadband or continuous spectra.