Editing Light-emitting diode (section)

{{Short description|Semiconductor and solid-state light source}}
{{About|the electronic device|specific use in lighting|LED lamp}}
{{Redirect2|LED|Led|other uses|LED (disambiguation)}}
{{Infobox electronic component
| name              = Light-emitting diode
| image             = File:RBG-LED.jpg|A white led (Gray Filament)
| caption           = Blue, green, and red LEDs in 5 mm diffused cases. [[#Types|There are many different variants]] of LEDs.
| working_principle = [[Electroluminescence]]
| inventor          = {{Plain list|
* [[H. J. Round]] (1907)<ref>{{cite web|url=http://www.myledpassion.com/History/hj-round.htm|title=HJ Round was a pioneer in the development of the LED|website=www.myledpassion.com|access-date=April 11, 2017|archive-date=October 28, 2020|archive-url=https://web.archive.org/web/20201028074225/http://www.myledpassion.com/History/hj-round.htm|url-status=usurped}}</ref>
* [[Oleg Losev]] (1927)<ref name="100-YEAR HISTORY">{{cite news| url=http://holly.orc.soton.ac.uk/fileadmin/downloads/100_years_of_optoelectronics__2_.pdf| title=The life and times of the LED — a 100-year history| date=April 2007| agency=The Optoelectronics Research Centre, University of Southampton| access-date=September 4, 2012| url-status=dead| archive-url=https://web.archive.org/web/20120915034646/http://holly.orc.soton.ac.uk/fileadmin/downloads/100_years_of_optoelectronics__2_.pdf| archive-date=September 15, 2012| df=mdy-all}}</ref>
* [[James R. Biard]] (1961)<ref>[http://www.freepatentsonline.com/3293513.pdf US Patent 3293513], "Semiconductor Radiant Diode", James R. Biard and Gary Pittman, Filed on Aug. 8th, 1962, Issued on Dec. 20th, 1966.</ref>
* [[Nick Holonyak]] (1962)<ref name="LEMELSON-MIT">{{cite news|url=http://web.mit.edu/invent/n-pressreleases/n-press-04LMP.html |title=Inventor is of Long-Lasting, Low-Heat Light Source Awarded $500,000 Lemelson-MIT Prize for Invention |date=April 21, 2004 |agency=Massachusetts Institute of Technology |access-date=December 21, 2011 |location=Washington, D.C. |url-status=dead |archive-url=https://web.archive.org/web/20111009111042/http://web.mit.edu/invent/n-pressreleases/n-press-04LMP.html |archive-date=October 9, 2011 }}</ref>
}}
| first_produced    = {{Start date and age|1962|10}}
| pins              = [[Anode]] and [[cathode]]
| symbol            = [[File:LED symbol.svg|class=skin-invert-image|150px]]
}}

[[File:LED, 5mm, green (en).svg|class=skin-invert-image|thumb|Parts of a conventional LED. The flat bottom surfaces of the anvil and post embedded inside the epoxy act as anchors, to prevent the conductors from being forcefully pulled out via mechanical strain or vibration.]]
[[File:Surface mount LED close up image.png|thumb|Close-up image of a [[SMD LED|surface-mount LED]]]]
[[File:LED Operation.ogg|thumb|Close-up of an LED with the voltage being increased and decreased to show a detailed view of its operation]]
[[File:Br20 1.jpg|thumb|alt=Modern LED [[Green retrofit|retrofit]] with E27 screw in base|A bulb-shaped modern retrofit [[LED lamp]] with aluminum [[heat sink]], a light [[Diffuser (optics)|diffusing]] dome and [[Edison screw|E27 screw]] base, using a built-in power supply working on [[Mains electricity|mains voltage]]]]

A '''light-emitting diode''' ('''LED''') is a [[semiconductor device]] that [[Light#Light sources|emits light]] when [[Electric current|current]] flows through it. [[Electron]]s in the semiconductor recombine with [[electron hole]]s, releasing energy in the form of [[photon]]s. The color of the light (corresponding to the energy of the photons) is determined by the energy required for electrons to cross the [[band gap]] of the [[semiconductor]].<ref>{{cite web |url=http://faculty.sites.uci.edu/chem1l/files/2013/11/RDGLED.pdf |work=[[University of California, Irvine]] |access-date=12 January 2019 |title=Light Emitting Diodes |last=Edwards |first=Kimberly D. |page=2 |archive-date=February 14, 2019 |archive-url=https://web.archive.org/web/20190214175634/http://faculty.sites.uci.edu/chem1l/files/2013/11/RDGLED.pdf |url-status=dead }}</ref> White light is obtained by using multiple semiconductors or a layer of light-emitting [[phosphor]] on the semiconductor device.<ref>{{cite web |url=https://www.lrc.rpi.edu/programs/nlpip/lightinganswers/led/whitelight.asp |title=How is white light made with LEDs? |work=[[Rensselaer Polytechnic Institute]] |author=Lighting Research Center |access-date=12 January 2019 |archive-date=May 2, 2021 |archive-url=https://web.archive.org/web/20210502084248/https://www.lrc.rpi.edu/programs/nlpip/lightinganswers/led/whiteLight.asp |url-status=dead }}</ref>

Appearing as practical electronic components in 1962, the earliest LEDs emitted low-intensity [[infrared]] (IR) light.<ref name=FirstPracticalLED>{{cite web |author1=Okon, Thomas M. |author2=Biard, James R. |title=The First Practical LED |url=http://edisontechcenter.org/lighting/LED/TheFirstPracticalLED.pdf |website=EdisonTechCenter.org |publisher=[[Edison Tech Center]] |date=2015 |access-date=2016-02-02}}</ref> Infrared LEDs are used in [[Remote control|remote-control]] circuits, such as those used with a wide variety of consumer electronics. The first visible-light LEDs were of low intensity and limited to red.

Early LEDs were often used as indicator lamps, replacing small [[Incandescent light bulb|incandescent bulbs]], and in [[seven-segment display]]s. Later developments produced LEDs available in [[Visible spectrum|visible]], [[ultraviolet]] (UV), and infrared wavelengths with high, low, or intermediate light output, for instance, white LEDs suitable for room and outdoor lighting. LEDs have also given rise to new types of displays and sensors, while their high switching rates are useful in advanced communications technology. LEDs have been used in diverse applications such as [[Navigation light|aviation lighting]], [[Christmas lights|fairy lights]], [[LED strip light|strip lights]], [[Automotive lighting#Light-emitting diodes (LED)|automotive headlamps]], advertising, [[stage lighting]], [[Lighting|general lighting]], [[Traffic light|traffic signals]], camera flashes, [[LED wallpaper|lighted wallpaper]], [[Grow light|horticultural grow lights]], and medical devices.<ref name="Aguilar">{{Cite book|pmid=18002450|doi= 10.1109/IEMBS.2007.4352784|year= 2007|last1= Peláez|first1= E. A|volume= 2007|pages= 2296–9|last2= Villegas|first2= E. R|title= 2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society|chapter= LED power reduction trade-offs for ambulatory pulse oximetry|isbn= 978-1-4244-0787-3|s2cid= 34626885 |issn = 1557-170X}}</ref>

LEDs have many advantages over incandescent light sources, including lower power consumption, a longer lifetime, improved physical robustness, smaller sizes, and faster switching. In exchange for these generally favorable attributes, disadvantages of LEDs include electrical limitations to low voltage and generally to DC (not AC) power, the inability to provide steady illumination from a pulsing DC or an AC electrical supply source, and a lesser maximum operating temperature and storage temperature.

LEDs are [[transducer]]s of electricity into light. They operate in reverse of [[photodiode]]s, which convert light into electricity.