A light-emitting diode (LED) is a
semiconductor A semiconductor material has an value falling between that of a , such as metallic copper, and an , such as glass. Its falls as its temperature rises; metals behave in the opposite way. Its conducting properties may be altered in useful ways ...
light source Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nano ...
that emits light when
current Currents or The Current may refer to: Science and technology * Current (fluid) A current in a fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. ...
flows through it.
Electron The electron is a subatomic particle (denoted by the symbol or ) whose electric charge is negative one elementary charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are general ...

s in the semiconductor recombine with
electron hole When an electron leaves a helium atom, it leaves an electron hole in its place. This causes the helium atom to become positively charged. In physics Physics is the natural science that studies matter, its Elementary particle, fundamenta ...
s, releasing energy in the form of
photon The photon ( el, φῶς, phōs, light) is a type of elementary particle In , an elementary particle or fundamental particle is a that is not composed of other particles. Particles currently thought to be elementary include the fundamental s ...

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 In solid-state physics Solid-state physics is the study of rigid matter, or solids, through methods such as quantum mechanics, crystallography, electromagnetism, and metallurgy. It is the largest branch of condensed matter physics. Solid-state ...

band gap
of the semiconductor. White light is obtained by using multiple semiconductors or a layer of light-emitting phosphor on the semiconductor device. Appearing as practical electronic components in 1962, the earliest LEDs emitted low-intensity
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

(IR) light. Infrared LEDs are used in
remote-control In electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. It uses active devices to control electron flow by amplifier, ampl ...
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 , and in
seven-segment display A seven-segment display is a form of electronic display device s, LED display and Vacuum fluorescent display, VF display, top to bottom. A display device is an output device for presentation of information in visual or Touch, tactile form (the la ...
s. Recent developments have produced LEDs available in
visible Visibility is in meteorology, a measure of the distance at which an object or light can be seen. Visibility may also refer to: * Visual perception ** Naked-eye visibility * A measure of turbidity in water quality control * Interferometric visibili ...
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that stud ...

(UV), and infrared wavelengths, with high, low, or intermediate light output, for instance white LEDs suitable for room and outdoor area lighting. LEDs have also given rise to new types of displays and sensors, while their high switching rates are useful in advanced communications technology with applications as diverse as aviation lighting, fairy lights, automotive headlamps, advertising, ,
traffic signal Traffic lights, traffic signals, stoplights or robots (as they are known in South Africa) are signalling devices positioned at road intersections, pedestrian crossing A pedestrian crossing (primarily British English) or crosswalk (primar ...

traffic signal
s, camera flashes, lighted wallpaper, horticultural grow lights, and medical devices. LEDs have many advantages over incandescent light sources, including lower power consumption, longer lifetime, improved physical robustness, smaller size, 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, inability to provide steady illumination from a pulsing DC or an AC electrical supply source, and lesser maximum operating temperature and storage temperature. In contrast to LEDs, incandescent lamps can be made to intrinsically run at virtually any supply voltage, can utilize either AC or DC current interchangeably, and will provide steady illumination when powered by AC or pulsing DC even at a frequency as low as 50 Hz. LEDs usually need electronic support components to function, while an incandescent bulb can and usually does operate directly from an unregulated DC or AC power source.


Discoveries and early devices

Electroluminescence Electroluminescence (EL) is an optical phenomenon and electrical phenomenon in which a material emits light in response to the passage of an electric current or to a strong electric field. This is distinct from black body light emission resulting f ...
as a phenomenon was discovered in 1907 by the English experimenter H. J. Round of Marconi Labs, using a crystal of
silicon carbide Silicon carbide (SiC), also known as carborundum (), is a semiconductor containing silicon and carbon. It occurs in nature as the extremely rare mineral moissanite. Synthetic SiC powder has been mass-produced since 1893 for use as an abrasive. Gra ...

silicon carbide
and a
cat's-whisker detector A crystal detector is an obsolete electronic component An electronic component is any basic discrete device or physical entity in an electronic system Electronic may refer to: *Electronics, the science of how to control electric energy in s ...
. Russian inventor
Oleg Losev Oleg Vladimirovich Losev (russian: Оле́г Влади́мирович Ло́сев, sometimes spelled Lossev or Lossew in English) (10 May 1903 – 22 January 1942) was a Russian scientist A scientist is a person who conducts Scientific me ...
reported creation of the first LED in 1927. English translation: His research was distributed in Soviet, German and British scientific journals, but no practical use was made of the discovery for several decades. In 1936, Georges Destriau observed that electroluminescence could be produced when
zinc sulphide Zinc sulfide (or zinc sulphide) is an inorganic compound In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, ...
(ZnS) powder is suspended in an insulator and an alternating electrical field is applied to it. In his publications, Destriau often referred to luminescence as Losev-Light. Destriau worked in the laboratories of Madame
Marie Curie Marie Salomea Skłodowska Curie ( ; ; , born Maria Salomea Skłodowska ; 7 November 1867 – 4 July 1934) was a Polish and naturalized-French physicist A physicist is a scientist A scientist is a person who conducts Scientific meth ...

Marie Curie
, also an early pioneer in the field of luminescence with research on
radium Radium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science tha ...

.McGraw-Hill Concise Encyclopedia of Physics: electroluminescence. (n.d.) McGraw-Hill Concise Encyclopedia of Physics. (2002). Hungarian Zoltán Bay together with György Szigeti pre-empted
LED lighting An 80W Chips on board (COB) LED module from an industrial light luminaire, thermally bonded to the heat sink An LED lamp or LED light bulb is an electric light An electric light is a device that produces visible light from electric p ...

LED lighting
in Hungary in 1939 by patenting a lighting device based on SiC, with an option on boron carbide, that emitted white, yellowish white, or greenish white depending on impurities present.
Kurt Lehovec Kurt Lehovec (June 12, 1918 – February 17, 2012) was one of the pioneers of the integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circu ...

Kurt Lehovec
, Carl Accardo, and Edward Jamgochian explained these first LEDs in 1951 using an apparatus employing
SiC The Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, ...

crystals with a current source of a battery or a pulse generator and with a comparison to a variant, pure, crystal in 1953. Rubin Braunstein of the
Radio Corporation of America The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric General Electric Company (GE) is an American Multinati ...
reported on infrared emission from
gallium arsenide Gallium Gallium is a chemical element with the Symbol (chemistry), symbol Ga and atomic number 31. Discovered by France, French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in boron group, group 13 of the periodic ta ...

gallium arsenide
(GaAs) and other semiconductor alloys in 1955. Braunstein observed infrared emission generated by simple diode structures using
gallium antimonide Gallium antimonide (GaSb) is a semiconductor, semiconducting compound of gallium and antimony of the III-V family. It has a lattice constant of about 0.61 nanometre, nm. It has a band gap of 0.67 eV. History The intermetallic compound GaSb was firs ...
(GaSb), GaAs,
indium phosphide Indium phosphide (InP) is a binary semiconductor A semiconductor material has an Electrical resistivity and conductivity, electrical conductivity value falling between that of a Electrical conductor, conductor, such as metallic copper, and an i ...

indium phosphide
(InP), and
silicon-germaniumSiGe ( or ), or silicon-germanium, is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, ...
(SiGe) alloys at room temperature and at 77 
kelvin The kelvin is the base unit of temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal en ...

s. In 1957, Braunstein further demonstrated that the rudimentary devices could be used for non-radio communication across a short distance. As noted by Kroemer Braunstein "…had set up a simple optical communications link: Music emerging from a record player was used via suitable electronics to modulate the forward current of a GaAs diode. The emitted light was detected by a PbS diode some distance away. This signal was fed into an audio amplifier and played back by a loudspeaker. Intercepting the beam stopped the music. We had a great deal of fun playing with this setup." This setup presaged the use of LEDs for
optical communication Optical communication, also known as optical telecommunication, is communication Communication (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was ...

optical communication
applications. In September 1961, while working at
Texas Instruments Texas Instruments Incorporated (TI) is an America The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America North America is a ...
Dallas Dallas (), colloquially referred to as Big D, is a city in the U.S. state of Texas and the largest city in and County seat, seat of Dallas County, Texas, Dallas County, with portions extending into Collin County, Texas, Collin, Denton County, ...

Texas Texas (, ; Spanish Spanish may refer to: * Items from or related to Spain: **Spaniards, a nation and ethnic group indigenous to Spain **Spanish language **Spanish cuisine Other places * Spanish, Ontario, Canada * Spanish River (disambigu ...

, James R. Biard and Gary Pittman discovered near-infrared (900 nm) light emission from a
tunnel diode A tunnel diode or Esaki diode is a type of semiconductor diode Various semiconductor diodes. Bottom: A bridge rectifier. In most diodes, a white or black painted band identifies the cathode into which electrons will flow when the diode is co ...

tunnel diode
they had constructed on a GaAs substrate. By October 1961, they had demonstrated efficient light emission and signal coupling between a GaAs p-n junction light emitter and an electrically isolated semiconductor photodetector. On August 8, 1962, Biard and Pittman filed a patent titled "Semiconductor Radiant Diode" based on their findings, which described a zinc-diffused
p–n junction A p–n junction is a boundary or interface between two types of semiconductor material A semiconductor material has an electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) ...
LED with a spaced
cathode A cathode is the from which a leaves a polarized electrical device. This definition can be recalled by using the ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in which positive charges move. Electrons ha ...
contact to allow for efficient emission of infrared light under
forward bias Forward is a relative direction Body relative directions (also known as egocentric coordinates) are geometrical orientations relative to a body such as a human Humans (''Homo sapiens'') are the most populous and widespread species of pr ...
. After establishing the priority of their work based on engineering notebooks predating submissions from G.E. Labs,
RCA The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric General Electric Company (GE) is an American multinatio ...
Research Labs,
IBM International Business Machines Corporation (IBM) is an American multinational technology company headquartered in Armonk, New York, with operations in over 170 countries. The company began in 1911, founded in Endicott, New York, as the C ...

Research Labs,
Bell Labs Nokia Bell Labs (formerly named Bell Labs Innovations (1996–2007), AT&T Bell Laboratories (1984–1996) and Bell Telephone Laboratories (1925–1984)) is an American industrial research and scientific development company A company, ab ...
, and Lincoln Lab at
MIT Massachusetts Institute of Technology (MIT) is a private land-grant research university A research university is a university A university ( la, universitas, 'a whole') is an educational institution, institution of higher education, hi ...

, the
U.S. patent office The United States Patent and Trademark Office (USPTO) is an agency in the U.S. Department of Commerce that issues patent NPOV disputes from March 2021 A patent is a Title (property), title that gives its owner the legal right to exclude o ...
issued the two inventors the patent for the GaAs infrared light-emitting diode (U.S. Paten
, the first practical LED. Immediately after filing the patent,
Texas Instruments Texas Instruments Incorporated (TI) is an America The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America North America is a ...
(TI) began a project to manufacture infrared diodes. In October 1962, TI announced the first commercial LED product (the SNX-100), which employed a pure GaAs crystal to emit an 890 nm light output. In October 1963, TI announced the first commercial hemispherical LED, the SNX-110. The first visible-spectrum (red) LED was demonstrated by J W Allen and R J Cherry in late 1961 at the SERL in Baldock, UK. This work was reported in Journal of Physics and Chemistry of Solids Volume 23, Issue 5, May 1962, Pages 509–511. Another early device was demonstrated by Nick Holonyak, Jr. on October 9, 1962, while he was working for
General Electric General Electric Company (GE) is an American Multinational corporation, multinational Conglomerate (company), conglomerate incorporated in New York State and headquartered in Boston. Until 2021, the company operated through GE Aviation, aviat ...
Syracuse, New York Syracuse ( ) is a city A city is a large .Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedia''. 2nd edition. London: Routledge. It can be d ...
. Holonyak and Bevacqua reported this LED in the journal ''Applied Physics Letters'' on December 1, 1962. M. George Craford, a former graduate student of Holonyak, invented the first yellow LED and improved the brightness of red and red-orange LEDs by a factor of ten in 1972. In 1976, T. P. Pearsall designed the first high-brightness, high-efficiency LEDs for optical fiber telecommunications by inventing new semiconductor materials specifically adapted to optical fiber transmission wavelengths.

Initial commercial development

The first commercial visible-wavelength LEDs were commonly used as replacements for
incandescent Incandescence is the emission of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spaceti ...

and , and in
seven-segment display A seven-segment display is a form of electronic display device s, LED display and Vacuum fluorescent display, VF display, top to bottom. A display device is an output device for presentation of information in visual or Touch, tactile form (the la ...
s, first in expensive equipment such as laboratory and electronics test equipment, then later in such appliances as calculators, TVs, radios, telephones, as well as watches (see list of signal uses). Until 1968, visible and infrared LEDs were extremely costly, in the order of
US$ The United States dollar (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, ...
200 per unit, and so had little practical use.
Hewlett-Packard The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California Palo Alto (; Spanish language, Spanish for "tall stick" ...

(HP) was engaged in
research and development Research and development (R&D, R+D), known in Europe Europe is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geogra ...
(R&D) on practical LEDs between 1962 and 1968, by a research team under Howard C. Borden, Gerald P. Pighini and
Mohamed M. Atalla Mohamed M. Atalla ( ar, محمد عطاالله; August 4, 1924 – December 30, 2009) was an Egyptian-American engineer, physical chemist Physical chemistry is the study of macroscopic The macroscopic scale is the length scale on which ...

Mohamed M. Atalla
at HP Associates and
HP Labs HP Labs is the exploratory and advanced research group for HP Inc. HP Inc. is an American multinational information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and ...
. During this time, Atalla launched a material science investigation program on
gallium arsenide Gallium Gallium is a chemical element with the Symbol (chemistry), symbol Ga and atomic number 31. Discovered by France, French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in boron group, group 13 of the periodic ta ...

gallium arsenide
gallium arsenide phosphideGallium arsenide phosphide (1−xx) is a semiconductor material, an alloy of gallium arsenide Gallium arsenide (GaAs) is a III-V direct band gap semiconductor with a Zincblende (crystal structure), zinc blende crystal structure. Gallium arsenid ...
(GaAsP) and
indium arsenide Indium arsenide, InAs, or indium monoarsenide, is a semiconductor A semiconductor material has an Electrical resistivity and conductivity, electrical conductivity value falling between that of a Electrical conductor, conductor, such as metallic c ...

indium arsenide
(InAs) devices at HP, and they collaborated with
Monsanto Company The Monsanto Company () was an American agrochemical and agricultural biotechnology corporation founded in 1901. In 2018, it was acquired by Bayer as part of its crop science division. It was headquartered in Creve Coeur, Missouri. Monsanto ...
on developing the first usable LED products. The first usable LED products were HP's
LED display A LED display is a flat panel display A flat-panel display (FPD) is an electronic display device used to enable people to see content (still images, moving images, text, or other visual material) in a range of entertainment, consumer electr ...

LED display
and Monsanto's LED indicator lamp, both launched in 1968. Monsanto was the first organization to mass-produce visible LEDs, using GaAsP in 1968 to produce red LEDs suitable for indicators. Monsanto had previously offered to supply HP with GaAsP, but HP decided to grow its own GaAsP. In February 1969, Hewlett-Packard introduced the HP Model 5082-7000 Numeric Indicator, the first LED device to use
integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuit 200px, A circuit built on a printed circuit board (PCB). An electronic circuit is composed of indiv ...

integrated circuit
(integrated ) technology. It was the first intelligent LED display, and was a revolution in
digital display s, LED An LED A light-emitting diode (LED) is a semiconductor A semiconductor material has an Electrical resistivity and conductivity, electrical conductivity value falling between that of a Electrical conductor, conductor, such as me ...
technology, replacing the
Nixie tube A Nixie tube ( ), or cold cathode display, is an electronic device used for displaying numerals or other information using glow discharge. The glass tube contains a wire-mesh anode An anode is an electrode through which the conventional ...
and becoming the basis for later LED displays. Atalla left HP and joined
Fairchild Semiconductor Fairchild Semiconductor International, Inc. was an American semiconductor A semiconductor material has an electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental pr ...
in 1969. He was the vice president and general manager of the Microwave & Optoelectronics division, from its inception in May 1969 up until November 1971. He continued his work on LEDs, proposing they could be used for indicator lights and
optical reader An optical reader is a device found within most computer image scanner, scanners that captures visual information and translates the image into digital data, digital information the computer is capable of understanding and displaying. An example o ...
s in 1971. In the 1970s, commercially successful LED devices at less than five cents each were produced by Fairchild Optoelectronics. These devices employed compound
semiconductor chip An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Transistor count, Larg ...
s fabricated with the
planar process The planar process is a manufacturing process used in the semiconductor industry to build individual components of a transistor file:MOSFET Structure.png, upright=1.4, Metal-oxide-semiconductor field-effect transistor (MOSFET), showing Metal g ...
(developed by
Jean HoerniJean Amédée Hoerni (September 26, 1924 – January 12, 1997) was a Swiss-American engineer. He was a silicon transistor pioneer, and a member of the " traitorous eight". He developed the planar process, an important technology for reliably fabr ...
, based on Atalla's
surface passivation Water droplet lying on a damask. Surface tension">damask.html" ;"title="Water droplet lying on a damask">Water droplet lying on a damask. Surface tension is high enough to prevent floating below the textile. A surface, as the term is most gener ...
method). The combination of planar processing for
chip fabrication Semiconductor device fabrication is the process used to manufacture semiconductor devices, typically the metal–oxide–semiconductor (MOS) devices used in the integrated circuit (IC) chips that are present in everyday electrical and electro ...
and innovative
packaging Packaging is the science Science () is a systematic enterprise that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about the universe."... modern science is a disco ...
methods enabled the team at Fairchild led by optoelectronics pioneer Thomas Brandt to achieve the needed cost reductions. LED producers continue to use these methods. The early red LEDs were bright enough only for use as indicators, as the light output was not enough to illuminate an area. Readouts in calculators were so small that plastic lenses were built over each digit to make them legible. Later, other colors became widely available and appeared in appliances and equipment. Early LEDs were packaged in metal cases similar to those of transistors, with a glass window or lens to let the light out. Modern indicator LEDs are packed in transparent molded plastic cases, tubular or rectangular in shape, and often tinted to match the device color. Infrared devices may be dyed, to block visible light. More complex packages have been adapted for efficient heat dissipation in high-power LEDs. Surface-mounted LEDs further reduce the package size. LEDs intended for use with
fiber optics An optical fiber (or fibre in British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codificati ...
cables may be provided with an optical connector.

Blue LED

The first blue-violet LED using magnesium-doped
gallium nitride Gallium nitride () is a binary boron group, III/nitrogen group, V direct bandgap semiconductor commonly used in blue light-emitting diodes since the 1990s. The compound (chemistry), compound is a very hard material that has a Wurtzite crystal st ...
was made at
Stanford University Stanford University, officially Leland Stanford Junior University, is a private Private or privates may refer to: Music * "In Private "In Private" was the third single in a row to be a charting success for United Kingdom, British singer Du ...

Stanford University
in 1972 by Herb Maruska and Wally Rhines, doctoral students in materials science and engineering. At the time Maruska was on leave from
RCA Laboratories The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric General Electric Company (GE) is an American Multination ...
, where he collaborated with Jacques Pankove on related work. In 1971, the year after Maruska left for Stanford, his RCA colleagues Pankove and Ed Miller demonstrated the first blue electroluminescence from zinc-doped gallium nitride, though the subsequent device Pankove and Miller built, the first actual gallium nitride light-emitting diode, emitted green light. In 1974 the
U.S. Patent Office The United States Patent and Trademark Office (USPTO) is an agency in the U.S. Department of Commerce that issues patent NPOV disputes from March 2021 A patent is a Title (property), title that gives its owner the legal right to exclude o ...
awarded Maruska, Rhines and Stanford professor David Stevenson a patent for their work in 1972 (U.S. Paten
US3819974 A
. Today, magnesium-doping of gallium nitride remains the basis for all commercial blue LEDs and
laser diode A packaged laser diode shown with a penny for scale The laser diode chip removed and placed on the eye of a needle for scale A laser diode (LD, also injection laser diode or ILD, or diode laser) is a semiconductor A semiconductor mater ...

laser diode
s. In the early 1970s, these devices were too dim for practical use, and research into gallium nitride devices slowed. In August 1989,
Cree The Cree ( cr, Néhinaw, script=Latn, , etc.; french: link=no, Cri) are a North American Indigenous people. They live primarily in Canada Canada is a country in the northern part of North America. Its Provinces and territories of Can ...
introduced the first commercially available blue LED based on the
indirect bandgapIn semiconductor physics, the band gap In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap general ...
semiconductor, silicon carbide (SiC). SiC LEDs had very low efficiency, no more than about 0.03%, but did emit in the blue portion of the visible light spectrum. In the late 1980s, key breakthroughs in GaN
epitaxial Epitaxy refers to a type of crystal growth or material deposition in which new crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic ...
growth and p-type doping ushered in the modern era of GaN-based
optoelectronic Opto-electronics (or optronics) is the study and application of electronic devices and systems that source, detect and control light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that ...
devices. Building upon this foundation, Theodore Moustakas at Boston University patented a method for producing high-brightness blue LEDs using a new two-step process in 1991. Two years later, in 1993, high-brightness blue LEDs were demonstrated by
Shuji Nakamura is a Japanese-born American electronic engineer Printed circuit board Electronic engineering (also called electronics and communications engineering) is an electrical engineering discipline which utilizes nonlinear and active electrical com ...

Shuji Nakamura
of using a gallium nitride growth process. In parallel,
Isamu Akasaki was a Japanese engineer and physicist, specializing in the field of semiconductor technology and Nobel Prize laureate, best known for inventing the bright gallium nitride ( GaN) p-n junction blue LED A light-emitting diode (LED) is ...
Hiroshi Amano is a Japanese physicist, engineer and inventor specializing in the field of semiconductor technology. For his work he was awarded the 2014 Nobel Prize in Physics together with Isamu Akasaki and Shuji Nakamura for "the invention of efficient blu ...
Nagoya University , abbreviated to or NU, is a Japanese national research university A research university is a university A university ( la, universitas, 'a whole') is an educational institution, institution of higher education, higher (or Tertiary educatio ...
were working on developing the important
GaN The word Gan or the initials GAN may refer to: Places * Gáň, a village and municipality in Galanta District, Trnava Region, south-west Slovakia * Gan Island, an island in the Addu Atoll in the Indian Ocean that used to be an RAF airbase * Ga ...
deposition on sapphire substrates and the demonstration of p-type doping of GaN. This new development revolutionized LED lighting, making high-power blue light sources practical, leading to the development of technologies like
Blu-ray The Blu-ray Disc (BD), often known simply as Blu-ray, is a digital Digital usually refers to something using digits, particularly binary digits. Technology and computing Hardware *Digital electronics Digital electronics is a field of elec ...
. Nakamura was awarded the 2006
Millennium Technology Prize The Millennium Technology Prize ( fi, Millennium-teknologiapalkinto) is one of the world's largest technology prizes. It is awarded once every two years by Technology Academy Finland, an independent fund established by Finnish industry and the F ...
for his invention. Nakamura,
Hiroshi Amano is a Japanese physicist, engineer and inventor specializing in the field of semiconductor technology. For his work he was awarded the 2014 Nobel Prize in Physics together with Isamu Akasaki and Shuji Nakamura for "the invention of efficient blu ...
Isamu Akasaki was a Japanese engineer and physicist, specializing in the field of semiconductor technology and Nobel Prize laureate, best known for inventing the bright gallium nitride ( GaN) p-n junction blue LED A light-emitting diode (LED) is ...
were awarded the
Nobel Prize in Physics The Nobel Prize in Physics is a yearly award given by the Royal Swedish Academy of Sciences for those who have made the most outstanding contributions for mankind in the field of physics. It is one of the five Nobel Prizes established by the will ...
in 2014 for the invention of the blue LED. In 2015, a US court ruled that three companies had infringed Moustakas's prior patent, and ordered them to pay licensing fees of not less than US$13 million. In 1995, at the
Cardiff University Cardiff University ( cy, Prifysgol Caerdydd) is a public research university in Cardiff, Wales. Founded in 1883 as the University College of South Wales and Monmouthshire (University College Cardiff from 1972), it became a founding college of the U ...
Laboratory (GB) investigated the efficiency and reliability of high-brightness LEDs and demonstrated a "transparent contact" LED using
indium tin oxideIndium tin oxide (ITO) is a ternary composition Ternary (from Latin ''ternarius'') is an adjective meaning "composed of three 3 is a number, numeral, and glyph. 3, three, or III may also refer to: * AD 3, the third year of the AD era * 3 BC, th ...
(ITO) on (AlGaInP/GaAs). In 2001 and 2002, processes for growing
gallium nitride Gallium nitride () is a binary boron group, III/nitrogen group, V direct bandgap semiconductor commonly used in blue light-emitting diodes since the 1990s. The compound (chemistry), compound is a very hard material that has a Wurtzite crystal st ...
(GaN) LEDs on
silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...

were successfully demonstrated. In January 2012,
Osram Osram Licht AG (stylized as OSRAM) is a globally active German company headquartered in Munich Munich ( ; german: München ; bar, Minga ) is the capital and most populous city of Bavaria Bavaria (; german: Bayern, , officially the F ...

demonstrated high-power InGaN LEDs grown on silicon substrates commercially, and GaN-on-silicon LEDs are in production at Plessey Semiconductors. As of 2017, some manufacturers are using SiC as the substrate for LED production, but sapphire is more common, as it has the most similar properties to that of gallium nitride, reducing the need for patterning the sapphire wafer (patterned wafers are known as epi wafers).
Samsung The Samsung Group (or simply Samsung) ( ko, 삼성) is a South Korean Multinational corporation, multinational manufacturing Conglomerate (company), conglomerate headquartered in Samsung Town, Seoul, South Korea. It comprises numerous affil ...

, the
University of Cambridge , mottoeng = Literal: From here, light and sacred draughts. Non literal: From this place, we gain enlightenment and precious knowledge. , established = , other_name = The Chancellor, Masters and Scholars of ...
, and
Toshiba is a Japanese multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational state, a sovereign st ...
are performing research into GaN on Si LEDs. Toshiba has stopped research, possibly due to low yields. Some opt towards epitaxy, which is difficult on
silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...

, while others, like the University of Cambridge, opt towards a multi-layer structure, in order to reduce (crystal) lattice mismatch and different thermal expansion ratios, in order to avoid cracking of the LED chip at high temperatures (e.g. during manufacturing), reduce heat generation and increase luminous efficiency. Sapphire substrate patterning can be carried out with
nanoimprint lithography Nanoimprint lithography (NIL) is a method of fabricating nanometer scale patterns. It is a simple nanolithography process with low cost, high throughput and high resolution. It creates patterns by mechanical deformation of imprint resist and subse ...
. GaN-on-Si is desirable since it takes advantage of existing semiconductor manufacturing infrastructure, however, it is difficult to achieve. It also allows for the wafer-level packaging of LED dies resulting in extremely small LED packages.https://web.archive.org/web/20140712100725/https://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/lester_substrate-pkg_tampa2014.pdf GaN is often deposited using
Metalorganic vapour-phase epitaxy Metalorganic vapour-phase epitaxy (MOVPE), also known as organometallic Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a ...
(MOCVD), and it also utilizes Lift-off.

White LEDs and the illumination breakthrough

Even though white light can be created using individual red, green and blue LEDs, this results in poor color rendering, since only three narrow bands of wavelengths of light are being emitted. The attainment of high efficiency blue LEDs was quickly followed by the development of the first
white LED A light-emitting diode (LED) is a semiconductor light source that emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The col ...
. In this device a :Ce (known as "YAG" or Ce:YAG phosphor) cerium-doped phosphor coating produces yellow light through fluorescence. The combination of that yellow with remaining blue light appears white to the eye. Using different phosphors produces green and red light through fluorescence. The resulting mixture of red, green and blue is perceived as white light, with improved color rendering compared to wavelengths from the blue LED/YAG phosphor combination. The first white LEDs were expensive and inefficient. However, the light output of LEDs has increased exponential growth, exponentially. The latest research and development has been propagated by Japanese manufacturers such as Panasonic, and Nichia, and by Korean and Chinese manufacturers such as
Samsung The Samsung Group (or simply Samsung) ( ko, 삼성) is a South Korean Multinational corporation, multinational manufacturing Conglomerate (company), conglomerate headquartered in Samsung Town, Seoul, South Korea. It comprises numerous affil ...

, Solstice, Kingsun, Hoyol and others. This trend in increased output has been called Haitz's law after Roland Haitz. Light output and efficiency of blue and near-ultraviolet LEDs rose and the cost of reliable devices fell. This led to relatively high-power white-light LEDs for illumination, which are replacing incandescent and fluorescent lighting. Experimental white LEDs were demonstrated in 2014 to produce 303 lumens per watt of electricity (lm/W); some can last up to 100,000 hours. However, commercially available LEDs have an efficiency of up to 223 lm/W as of 2018. A previous record of 135 lm/W was achieved by Nichia in 2010. Compared to incandescent bulbs, this is a huge increase in electrical efficiency, and even though LEDs are more expensive to purchase, overall lifetime cost is significantly cheaper than that of incandescent bulbs. The LED chip is encapsulated inside a small, plastic, white mold. It can be encapsulated using resin (polyurethane-based), silicone, or epoxy containing (powdered) Cerium-doped YAG phosphor. After allowing the solvents to evaporate, the LEDs are often tested, and placed on tapes for SMT placement equipment for use in LED light bulb production. Encapsulation is performed after probing, dicing, die transfer from wafer to package, and wire bonding or flip chip mounting, perhaps using Indium tin oxide, a transparent electrical conductor. In this case, the bond wire(s) are attached to the ITO film that has been deposited in the LEDs. Some "remote phosphor" LED light bulbs use a single plastic cover with YAG phosphor for several blue LEDs, instead of using phosphor coatings on single-chip white LEDs. The temperature of the phosphor during operation and how it is applied limits the size of an LED die. Wafer-level packaging, Wafer-level packaged white LEDs allow for extremely small LEDs.

Physics of light production and emission

In a light emitting diode, the recombination of electrons and electron holes in a semiconductor produces light (be it infrared, visible or UV), a process called "electroluminescence". The wavelength of the light depends on the energy
band gap In solid-state physics Solid-state physics is the study of rigid matter, or solids, through methods such as quantum mechanics, crystallography, electromagnetism, and metallurgy. It is the largest branch of condensed matter physics. Solid-state ...

band gap
of the semiconductors used. Since these materials have a high index of refraction, design features of the devices such as special optical coatings and die shape are required to efficiently emit light. Unlike a laser, the light emitted from an LED is neither spectrally Coherence (physics), coherent nor even highly monochromatic. However, its Spectrum#Electromagnetic spectrum, spectrum is sufficiently narrow that it appears to the color vision, human eye as a pure (Colorfulness#Saturation, saturated) color. Also unlike most lasers, its radiation is not Coherence (physics)#Spatial coherence, spatially coherent, so it cannot approach the very high Radiance, brightnesses characteristic of lasers.


By Light-emitting diode physics#Materials, selection of different semiconductor materials, single-color LEDs can be made that emit light in a narrow band of wavelengths from near-infrared through the visible spectrum and into the ultraviolet range. As the wavelengths become shorter, because of the larger band gap of these semiconductors, the operating voltage of the LED increases.

Blue and ultraviolet

Blue LEDs have an active region consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN, called cladding layers. By varying the relative In/Ga fraction in the InGaN quantum wells, the light emission can in theory be varied from violet to amber. Aluminium gallium nitride (AlGaN) of varying Al/Ga fraction can be used to manufacture the cladding and quantum well layers for ultraviolet LEDs, but these devices have not yet reached the level of efficiency and technological maturity of InGaN/GaN blue/green devices. If un-alloyed GaN is used in this case to form the active quantum well layers, the device emits near-ultraviolet light with a peak wavelength centred around 365 nm. Green LEDs manufactured from the InGaN/GaN system are far more efficient and brighter than green LEDs produced with non-nitride material systems, but practical devices still exhibit efficiency too low for high-brightness applications. With Aluminium gallium nitride, AlGaN and aluminium gallium indium nitride, AlGaInN, even shorter wavelengths are achievable. Near-UV emitters at wavelengths around 360–395 nm are already cheap and often encountered, for example, as black light lamp replacements for inspection of anti-counterfeiting UV watermarks in documents and bank notes, and for UV curing#LEDs, UV curing. Substantially more expensive, shorter-wavelength diodes are commercially available for wavelengths down to 240 nm. As the photosensitivity of microorganisms approximately matches the absorption spectrum of DNA, with a peak at about 260 nm, UV LED emitting at 250–270 nm are expected in prospective disinfection and sterilization devices. Recent research has shown that commercially available UVA LEDs (365 nm) are already effective disinfection and sterilization devices. UV-C wavelengths were obtained in laboratories using aluminium nitride (210 nm), boron nitride (215 nm) and diamond (235 nm).


There are two primary ways of producing white light-emitting diodes. One is to use individual LEDs that emit three primary colors—red, green and blue—and then mix all the colors to form white light. The other is to use a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light, similar to a fluorescent lamp. The yellow phosphor is cerium-doped YAG crystals suspended in the package or coated on the LED. This YAG phosphor causes white LEDs to appear yellow when off, and the space between the crystals allow some blue light to pass through in LEDs with partial phosphor conversion. Alternatively, white LEDs may use other phosphors like manganese(IV)-doped potassium fluorosilicate (PFS) or other engineered phosphors. PFS assists in red light generation, and is used in conjunction with conventional Ce:YAG phosphor. In LEDs with PFS phosphor, some blue light passes through the phosphors, the Ce:YAG phosphor converts blue light to green and red (yellow) light, and the PFS phosphor converts blue light to red light. The color, emission spectrum or color temperature of white phosphor converted and other phosphor converted LEDs can be controlled by changing the concentration of several phosphors that form a phosphor blend used in an LED package. The 'whiteness' of the light produced is engineered to suit the human eye. Because of Metamerism (color), metamerism, it is possible to have quite different spectra that appear white. The appearance of objects illuminated by that light may vary as the spectrum varies. This is the issue of color rendition, quite separate from color temperature. An orange or cyan object could appear with the wrong color and much darker as the LED or phosphor does not emit the wavelength it reflects. The best color rendition LEDs use a mix of phosphors, resulting in less efficiency and better color rendering.

RGB systems

Mixing red, green, and blue sources to produce white light needs electronic circuits to control the blending of the colors. Since LEDs have slightly different emission patterns, the color balance may change depending on the angle of view, even if the RGB sources are in a single package, so RGB diodes are seldom used to produce white lighting. Nonetheless, this method has many applications because of the flexibility of mixing different colors, and in principle, this mechanism also has higher quantum efficiency in producing white light. There are several types of multicolor white LEDs: :wiktionary:dichromatic, di-, trichromatic, tri-, and tetrachromatic white LEDs. Several key factors that play among these different methods include color stability, color rendering index, color rendering capability, and luminous efficacy. Often, higher efficiency means lower color rendering, presenting a trade-off between the luminous efficacy and color rendering. For example, the dichromatic white LEDs have the best luminous efficacy (120 lm/W), but the lowest color rendering capability. Although tetrachromatic white LEDs have excellent color rendering capability, they often have poor luminous efficacy. Trichromatic white LEDs are in between, having both good luminous efficacy (>70 lm/W) and fair color rendering capability. One of the challenges is the development of more efficient green LEDs. The theoretical maximum for green LEDs is 683 lumens per watt but as of 2010 few green LEDs exceed even 100 lumens per watt. The blue and red LEDs approach their theoretical limits. Multicolor LEDs also offer a new means to form light of different colors. Most color#Perception, perceivable colors can be formed by mixing different amounts of three primary colors. This allows precise dynamic color control. However, this type of LED's emission power exponential decay, decays exponentially with rising temperature, resulting in a substantial change in color stability. Such problems inhibit industrial use. Multicolor LEDs without phosphors cannot provide good color rendering because each LED is a narrowband source. LEDs without phosphor, while a poorer solution for general lighting, are the best solution for displays, either backlight of LCD, or direct LED based pixels. Dimming a multicolor LED source to match the characteristics of incandescent lamps is difficult because manufacturing variations, age, and temperature change the actual color value output. To emulate the appearance of dimming incandescent lamps may require a feedback system with color sensor to actively monitor and control the color.

Phosphor-based LEDs

This method involves coating LEDs of one color (mostly blue LEDs made of InGaN) with phosphors of different colors to form white light; the resultant LEDs are called phosphor-based or phosphor-converted white LEDs (pcLEDs). A fraction of the blue light undergoes the Stokes shift, which transforms it from shorter wavelengths to longer. Depending on the original LED's color, various color phosphors are used. Using several phosphor layers of distinct colors broadens the emitted spectrum, effectively raising the Color Rendering Index, color rendering index (CRI). Phosphor-based LEDs have efficiency losses due to heat loss from the Stokes shift and also other phosphor-related issues. Their luminous efficacies compared to normal LEDs depend on the spectral distribution of the resultant light output and the original wavelength of the LED itself. For example, the luminous efficacy of a typical YAG yellow phosphor based white LED ranges from 3 to 5 times the luminous efficacy of the original blue LED because of the human eye's greater sensitivity to yellow than to blue (as modeled in the luminosity function). Due to the simplicity of manufacturing, the phosphor method is still the most popular method for making high-intensity white LEDs. The design and production of a light source or light fixture using a monochrome emitter with phosphor conversion is simpler and cheaper than a complex #RGB systems, RGB system, and the majority of high-intensity white LEDs presently on the market are manufactured using phosphor light conversion. Among the challenges being faced to improve the efficiency of LED-based white light sources is the development of more efficient phosphors. As of 2010, the most efficient yellow phosphor is still the YAG phosphor, with less than 10% Stokes shift loss. Losses attributable to internal optical losses due to re-absorption in the LED chip and in the LED packaging itself account typically for another 10% to 30% of efficiency loss. Currently, in the area of phosphor LED development, much effort is being spent on optimizing these devices to higher light output and higher operation temperatures. For instance, the efficiency can be raised by adapting better package design or by using a more suitable type of phosphor. Conformal coating process is frequently used to address the issue of varying phosphor thickness. Some phosphor-based white LEDs encapsulate InGaN blue LEDs inside phosphor-coated epoxy. Alternatively, the LED might be paired with a remote phosphor, a preformed polycarbonate piece coated with the phosphor material. Remote phosphors provide more diffuse light, which is desirable for many applications. Remote phosphor designs are also more tolerant of variations in the LED emissions spectrum. A common yellow phosphor material is cerium-Doping (Semiconductors), doped yttrium aluminium garnet (Ce3+:YAG). White LEDs can also be made by coating near-ultraviolet (NUV) LEDs with a mixture of high-efficiency europium-based phosphors that emit red and blue, plus copper and aluminium-doped zinc sulfide (ZnS:Cu, Al) that emits green. This is a method analogous to the way fluorescent lamps work. This method is less efficient than blue LEDs with YAG:Ce phosphor, as the Stokes shift is larger, so more energy is converted to heat, but yields light with better spectral characteristics, which render color better. Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both methods offer comparable brightness. A concern is that UV light may leak from a malfunctioning light source and cause harm to human eyes or skin.

Other white LEDs

Another method used to produce experimental white light LEDs used no phosphors at all and was based on epitaxy, homoepitaxially grown zinc selenide (ZnSe) on a ZnSe substrate that simultaneously emitted blue light from its active region and yellow light from the substrate. A new style of wafers composed of gallium-nitride-on-silicon (GaN-on-Si) is being used to produce white LEDs using 200-mm silicon wafers. This avoids the typical costly sapphire Substrate (materials science), substrate in relatively small 100- or 150-mm wafer sizes.Next-Generation GaN-on-Si White LEDs Suppress Costs
Electronic Design, 19 November 2013
The sapphire apparatus must be coupled with a mirror-like collector to reflect light that would otherwise be wasted. It was predicted that since 2020, 40% of all GaN LEDs are made with GaN-on-Si. Manufacturing large sapphire material is difficult, while large silicon material is cheaper and more abundant. LED companies shifting from using sapphire to silicon should be a minimal investment.

Organic light-emitting diodes (OLEDs)

In an organic light-emitting diode (Organic light-emitting diode, OLED), the Electroluminescence, electroluminescent material composing the emissive layer of the diode is an organic compound. The organic material is electrically conductive due to the Delocalized electron, delocalization of Pi bond, pi electrons caused by Conjugated system, conjugation over all or part of the molecule, and the material therefore functions as an organic semiconductor. The organic materials can be small organic molecules in a crystalline phase (matter), phase, or polymers. The potential advantages of OLEDs include thin, low-cost displays with a low driving voltage, wide viewing angle, and high contrast and color gamut. Polymer LEDs have the added benefit of printable and flexible organic light-emitting diode, flexible displays. OLEDs have been used to make visual displays for portable electronic devices such as cellphones, digital cameras, lighting and televisions.


LEDs are made in different packages for different applications. A single or a few LED junctions may be packed in one miniature device for use as an indicator or pilot lamp. An LED array may include controlling circuits within the same package, which may range from a simple resistor, blinking or color changing control, or an addressable controller for RGB devices. Higher-powered white-emitting devices will be mounted on heat sinks and will be used for illumination. Alphanumeric displays in dot matrix or bar formats are widely available. Special packages permit connection of LEDs to optical fibers for high-speed data communication links.


These are mostly single-die LEDs used as indicators, and they come in various sizes from 2 mm to 8 mm, through-hole and surface mount packages. Typical current ratings range from around 1 mA to above 20 mA. Multiple LED dies attached to a flexible backing tape form an LED strip light. Common package shapes include round, with a domed or flat top, rectangular with a flat top (as used in bar-graph displays), and triangular or square with a flat top. The encapsulation may also be clear or tinted to improve contrast and viewing angle. Infrared devices may have a black tint to block visible light while passing infrared radiation. Ultra-high-output LEDs are designed for viewing in direct sunlight. 5 V and 12 V LEDs are ordinary miniature LEDs that have a series resistor for direct connection to a 5V or 12V supply.


High-power LEDs (HP-LEDs) or high-output LEDs (HO-LEDs) can be driven at currents from hundreds of mA to more than an ampere, compared with the tens of mA for other LEDs. Some can emit over a thousand lumens. LED Power density, power densities up to 300 W/cm2 have been achieved. Since overheating is destructive, the HP-LEDs must be mounted on a heat sink to allow for heat dissipation. If the heat from an HP-LED is not removed, the device fails in seconds. One HP-LED can often replace an incandescent bulb in a flashlight, or be set in an array to form a powerful LED lamp. Some well-known HP-LEDs in this category are the Nichia 19 series, Lumileds Rebel Led, Osram Opto Semiconductors Golden Dragon, and Cree X-lamp. As of September 2009, some HP-LEDs manufactured by Cree now exceed 105 lm/W. Examples for Haitz's law—which predicts an exponential rise in light output and efficacy of LEDs over time—are the CREE XP-G series LED, which achieved 105lm/W in 2009 and the Nichia 19 series with a typical efficacy of 140lm/W, released in 2010.


LEDs developed by Seoul Semiconductor can operate on AC power without a DC converter. For each half-cycle, part of the LED emits light and part is dark, and this is reversed during the next half-cycle. The efficacy of this type of HP-LED is typically 40lm/W. A large number of LED elements in series may be able to operate directly from line voltage. In 2009, Seoul Semiconductor released a high DC voltage LED, named 'Acrich MJT', capable of being driven from AC power with a simple controlling circuit. The low-power dissipation of these LEDs affords them more flexibility than the original AC LED design.

Application-specific variations


Flashing LEDs are used as attention seeking indicators without requiring external electronics. Flashing LEDs resemble standard LEDs but they contain an integrated voltage regulator and a multivibrator circuit that causes the LED to flash with a typical period of one second. In diffused lens LEDs, this circuit is visible as a small black dot. Most flashing LEDs emit light of one color, but more sophisticated devices can flash between multiple colors and even fade through a color sequence using RGB color mixing. Flashing SMD LEDs in the 0805 and other size formats have been available since early 2019.


Bi-color LEDs contain two different LED emitters in one case. There are two types of these. One type consists of two dies connected to the same two leads Antiparallel (electronics), antiparallel to each other. Current flow in one direction emits one color, and current in the opposite direction emits the other color. The other type consists of two dies with separate leads for both dies and another lead for common anode or cathode so that they can be controlled independently. The most common bi-color combination is red/traditional green, however, other available combinations include amber/traditional green, red/pure green, red/blue, and blue/pure green.

RGB tri-color

Tri-color LEDs contain three different LED emitters in one case. Each emitter is connected to a separate lead so they can be controlled independently. A four-lead arrangement is typical with one common lead (anode or cathode) and an additional lead for each color. Others, however, have only two leads (positive and negative) and have a built-in electronic controller. RGB color model, RGB LEDs consist of one red, one green, and one blue LED. By independently pulse-width modulation, adjusting each of the three, RGB LEDs are capable of producing a wide color gamut. Unlike dedicated-color LEDs, however, these do not produce pure wavelengths. Modules may not be optimized for smooth color mixing.


Decorative-multicolor LEDs incorporate several emitters of different colors supplied by only two lead-out wires. Colors are switched internally by varying the supply voltage.


Alphanumeric LEDs are available in seven-segment display, seven-segment, Starburst display, starburst, and Dot-matrix display, dot-matrix format. Seven-segment displays handle all numbers and a limited set of letters. Starburst displays can display all letters. Dot-matrix displays typically use 5×7 pixels per character. Seven-segment LED displays were in widespread use in the 1970s and 1980s, but rising use of liquid crystal displays, with their lower power needs and greater display flexibility, has reduced the popularity of numeric and alphanumeric LED displays.

Digital RGB

Digital RGB addressable LEDs contain their own "smart" control electronics. In addition to power and ground, these provide connections for data-in, data-out, clock and sometimes a strobe signal. These are connected in a Daisy chain (electrical engineering), daisy chain. Data sent to the first LED of the chain can control the brightness and color of each LED independently of the others. They are used where a combination of maximum control and minimum visible electronics are needed such as strings for Christmas and LED matrices. Some even have refresh rates in the kHz range, allowing for basic video applications. These devices are known by their part number (WS2812 being common) or a brand name such as Adafruit Industries#NeoPixel, NeoPixel.


An LED filament consists of multiple LED chips connected in series on a common longitudinal substrate that forms a thin rod reminiscent of a traditional incandescent filament. These are being used as a low-cost decorative alternative for traditional light bulbs that are being phased out in many countries. The filaments use a rather high voltage, allowing them to work efficiently with mains voltages. Often a simple rectifier and capacitive current limiting are employed to create a low-cost replacement for a traditional light bulb without the complexity of the low voltage, high current converter that single die LEDs need. Usually, they are packaged in bulb similar to the lamps they were designed to replace, and filled with inert gas at slightly lower than ambient pressure to remove heat efficiently and prevent corrosion.

Chip-on-board arrays

Surface-mounted LEDs are frequently produced in chip on board (COB) arrays, allowing better heat dissipation than with a single LED of comparable luminous output. The LEDs can be arranged around a cylinder, and are called "corn cob lights" because of the rows of yellow LEDs.

Considerations for use

Power sources

The current in an LED or other diodes rises exponentially with the applied voltage (see Shockley diode equation), so a small change in voltage can cause a large change in current. Current through the LED must be regulated by an external circuit such as a constant current source to prevent damage. Since most common power supplies are (nearly) constant-voltage sources, LED fixtures must include a power converter, or at least a current-limiting resistor. In some applications, the internal resistance of small batteries is sufficient to keep current within the LED rating.

Electrical polarity

Unlike a traditional incandescent lamp, an LED will light only when voltage is applied in the forward direction of the diode. No current flows and no light is emitted if voltage is applied in the reverse direction. If the reverse voltage exceeds the breakdown voltage, a large current flows and the LED will be damaged. If the reverse current is sufficiently limited to avoid damage, the reverse-conducting LED is a useful Hardware random number generator, noise diode.

Safety and health

Certain #Ultraviolet and blue LEDs, blue LEDs and cool-white LEDs can exceed safe limits of the so-called blue-light hazard as defined in eye safety specifications such as "ANSI/IESNA RP-27.1–05: Recommended Practice for Photobiological Safety for Lamp and Lamp Systems". One study showed no evidence of a risk in normal use at domestic illuminance, and that caution is only needed for particular occupational situations or for specific populations. In 2006, the International Electrotechnical Commission published ''IEC 62471 Photobiological safety of lamps and lamp systems'', replacing the application of early laser-oriented standards for classification of LED sources. While LEDs have the advantage over fluorescent lamps, in that they do not contain mercury (element), mercury, they may contain other hazardous metals such as lead and arsenic. In 2016 the American Medical Association (AMA) issued a statement concerning the possible adverse influence of blueish street lighting on the sleep-wake cycle of city-dwellers. Industry critics claim exposure levels are not high enough to have a noticeable effect.


* Efficiency: LEDs emit more lumens per watt than incandescent light bulbs. The efficiency of LED lighting fixtures is not affected by shape and size, unlike fluorescent light bulbs or tubes. * Color: LEDs can emit light of an intended color without using any color filters as traditional lighting methods need. This is more efficient and can lower initial costs. * Size: LEDs can be very small (smaller than 2 mm2) and are easily attached to printed circuit boards. * Warmup time: LEDs light up very quickly. A typical red indicator LED achieves full brightness in under a microsecond. LEDs used in communications devices can have even faster response times. * Cycling: LEDs are ideal for uses subject to frequent on-off cycling, unlike incandescent and fluorescent lamps that fail faster when cycled often, or high-intensity discharge lamps (HID lamps) that require a long time before restarting. * Dimming: LEDs can very easily be Dimmer, dimmed either by pulse-width modulation or lowering the forward current. This pulse-width modulation is why LED lights, particularly headlights on cars, when viewed on camera or by some people, seem to flash or flicker. This is a type of stroboscopic effect. * Cool light: In contrast to most light sources, LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat through the base of the LED. * Slow failure: LEDs mainly fail by dimming over time, rather than the abrupt failure of incandescent bulbs., US Department of Energy * Lifetime: LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours of useful life, though time to complete failure may be shorter or longer. Fluorescent tubes typically are rated at about 10,000 to 25,000 hours, depending partly on the conditions of use, and incandescent light bulbs at 1,000 to 2,000 hours. Several United States Department of Energy, DOE demonstrations have shown that reduced maintenance costs from this extended lifetime, rather than energy savings, is the primary factor in determining the payback period for an LED product. * Shock resistance: LEDs, being solid-state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs, which are fragile. * Focus: The solid package of the LED can be designed to focus (optics), focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner. For larger LED packages total internal reflection (TIR) lenses are often used to the same effect. However, when large quantities of light are needed many light sources are usually deployed, which are difficult to focus or collimate towards the same target.


* Temperature dependence: LED performance largely depends on the ambient temperature of the operating environment – or thermal management properties. Overdriving an LED in high ambient temperatures may result in overheating the LED package, eventually leading to device failure. An adequate heat sink is needed to maintain long life. This is especially important in automotive, medical, and military uses where devices must operate over a wide range of temperatures, and require low failure rates. * Voltage sensitivity: LEDs must be supplied with a voltage above their P–n junction#Forward bias, threshold voltage and a current below their rating. Current and lifetime change greatly with a small change in applied voltage. They thus require a current-regulated supply (usually just a series resistor for indicator LEDs). * Color rendition: Most cool-#Other white LEDs, white LEDs have spectra that differ significantly from a black body radiator like the sun or an incandescent light. The spike at 460 nm and dip at 500 nm can make the color of objects color vision, appear differently under cool-white LED illumination than sunlight or incandescent sources, due to metamerism (color), metamerism, red surfaces being rendered particularly poorly by typical phosphor-based cool-white LEDs. The same is true with green surfaces. The quality of color rendition of an LED is measured by the Color rendering index, Color Rendering Index (CRI). * Area light source: Single LEDs do not approximate a point source of light giving a spherical light distribution, but rather a Lambert's cosine law, lambertian distribution. So, LEDs are difficult to apply to uses needing a spherical light field; however, different fields of light can be manipulated by the application of different optics or "lenses". LEDs cannot provide divergence below a few degrees. * Light pollution: Because #White light, white LEDs emit more short wavelength light than sources such as high-pressure sodium vapor lamps, the increased blue and green sensitivity of scotopic vision means that white LEDs used in outdoor lighting cause substantially more sky glow. * LED droop, Efficiency droop: The efficiency of LEDs decreases as the electric current increases. Heating also increases with higher currents, which compromises LED lifetime. These effects put practical limits on the current through an LED in high power applications.Stevenson, Richard (August 2009
The LED’s Dark Secret: Solid-state lighting will not supplant the lightbulb until it can overcome the mysterious malady known as droop
''IEEE Spectrum''
* Impact on wildlife: LEDs are much more attractive to insects than sodium-vapor lights, so much so that there has been speculative concern about the possibility of disruption to food webs. LED lighting near beaches, particularly intense blue and white colors, can disorient turtle hatchlings and make them wander inland instead. The use of "turtle-safe lighting" LEDs that emit only at narrow portions of the visible spectrum is encouraged by conservancy groups in order to reduce harm. * Use in winter conditions: Since they do not give off much heat in comparison to incandescent lights, LED lights used for traffic control can have snow obscuring them, leading to accidents. * Thermal runaway: Parallel strings of LEDs will not share current evenly due to the manufacturing tolerances in their forward voltage. Running two or more strings from a single current source may result in LED failure as the devices warm up. If forward voltage binning is not possible, a circuit is required to ensure even distribution of current between parallel strands.


LED uses fall into four major categories: * Visual signals where light goes more or less directly from the source to the human eye, to convey a message or meaning * Lighting, Illumination where light is reflected from objects to give visual response of these objects * Measuring and interacting with processes involving no human vision * Narrow band light sensors where LEDs as light sensors, LEDs operate in a reverse-bias mode and respond to incident light, instead of emitting light

Indicators and signs

The energy conservation, low energy consumption, low maintenance and small size of LEDs has led to uses as status indicators and displays on a variety of equipment and installations. Large-area
LED display A LED display is a flat panel display A flat-panel display (FPD) is an electronic display device used to enable people to see content (still images, moving images, text, or other visual material) in a range of entertainment, consumer electr ...

LED display
s are used as stadium displays, dynamic decorative displays, and dynamic message signs on freeways. Thin, lightweight message displays are used at airports and railway stations, and as Destination sign, destination displays for trains, buses, trams, and ferries. One-color light is well suited for traffic lights and signals, exit signs, emergency vehicle lighting, ships' navigation lights, and Christmas lighting technology#LEDs, LED-based Christmas lights Because of their long life, fast switching times, and visibility in broad daylight due to their high output and focus, LEDs have been used in automotive brake lights and turn signals. The use in brakes improves safety, due to a great reduction in the time needed to light fully, or faster rise time, about 0.1 second faster than an incandescent bulb. This gives drivers behind more time to react. In a dual intensity circuit (rear markers and brakes) if the LEDs are not pulsed at a fast enough frequency, they can create a flicker fusion threshold#Visual phenomena, phantom array, where ghost images of the LED appear if the eyes quickly scan across the array. White LED headlamps are beginning to appear. Using LEDs has styling advantages because LEDs can form much thinner lights than incandescent lamps with parabolic reflectors. Due to the relative cheapness of low output LEDs, they are also used in many temporary uses such as glowsticks, throwies, and the photonic textile Lumalive. Artists have also used LEDs for LED art.


With the development of high-efficiency and high-power LEDs, it has become possible to use LEDs in lighting and illumination. To encourage the shift to LED lamps and other high-efficiency lighting, in 2008 the US Department of Energy created the L Prize competition. The Philips Lighting North America LED bulb won the first competition on August 3, 2011, after successfully completing 18 months of intensive field, lab, and product testing. Efficient lighting is needed for sustainable architecture. As of 2011, some LED bulbs provide up to 150 lm/W and even inexpensive low-end models typically exceed 50 lm/W, so that a 6-watt LED could achieve the same results as a standard 40-watt incandescent bulb. The lower heat output of LEDs also reduces demand on air conditioning systems. Worldwide, LEDs are rapidly adopted to displace less effective sources such as incandescent light bulb, incandescent lamps and compact fluorescent lamp, CFLs and reduce electrical energy consumption and its associated emissions. Solar powered LEDs are used as street lights and in Architectural lighting design, architectural lighting. The mechanical robustness and long lifetime are used in automotive lighting on cars, motorcycles, and Bicycle lighting#LEDs, bicycle lights. LED street lights are employed on poles and in parking garages. In 2007, the Italian village of Torraca was the first place to convert its street lighting to LEDs. Cabin lighting on recent Airbus and Boeing jetliners uses LED lighting. LEDs are also being used in airport and heliport lighting. LED airport fixtures currently include medium-intensity runway lights, runway centerline lights, taxiway centerline and edge lights, guidance signs, and obstruction lighting. LEDs are also used as a light source for Digital Light Processing, DLP projectors, and to backlight Liquid crystal display, LCD televisions (referred to as LED-backlit LCD display, LED TVs) and laptop displays. RGB LEDs raise the color gamut by as much as 45%. Screens for TV and computer displays can be made thinner using LEDs for backlighting. LEDs are small, durable and need little power, so they are used in handheld devices such as flashlights. LED strobe lights or camera flashes operate at a safe, low voltage, instead of the 250+ volts commonly found in xenon flashlamp-based lighting. This is especially useful in cameras on mobile phones, where space is at a premium and bulky voltage-raising circuitry is undesirable. LEDs are used for infrared illumination in night vision uses including security cameras. A ring of LEDs around a video camera, aimed forward into a retroreflective Projection screen, background, allows chroma keying in video productions. LEDs are used in Mining, mining operations, as cap lamps to provide light for miners. Research has been done to improve LEDs for mining, to reduce glare and to increase illumination, reducing risk of injury to the miners. LEDs are increasingly finding uses in medical and educational applications, for example as mood enhancement. NASA has even sponsored research for the use of LEDs to promote health for astronauts.

Data communication and other signalling

Light can be used to transmit data and analog signals. For example, lighting white LEDs can be used in systems assisting people to navigate in closed spaces while searching necessary rooms or objects. Assistive listening devices in many theaters and similar spaces use arrays of infrared LEDs to send sound to listeners' receivers. Light-emitting diodes (as well as semiconductor lasers) are used to send data over many types of Optical fiber, fiber optic cable, from digital audio over TOSLINK cables to the very high bandwidth fiber links that form the Internet backbone. For some time, computers were commonly equipped with IrDA interfaces, which allowed them to send and receive data to nearby machines via infrared. Because LEDs can frequency, cycle on and off millions of times per second, very high data bandwidth can be achieved. For that reason, Visible light communication, Visible Light Communication (VLC) has been proposed as an alternative to the increasingly competitive radio bandwidth. By operating in the visible part of the electromagnetic spectrum, data can be transmitted without occupying the frequencies of radio communications. The main characteristic of VLC, lies on the incapacity of light to surpass physical opaque barriers. This characteristic can be considered a weak point of VLC, due to the susceptibility of interference from physical objects, but is also one of its many strengths: unlike radio waves, light waves are confined in the enclosed spaces they are transmitted, which enforces a physical safety barrier that requires a receptor of that signal to have physical access to the place where the transmission is occurring. A promising application of VLC lies on the Indoor positioning system, Indoor Positioning System (IPS), an analogous to the GPS built to operate in enclosed spaces where the satellite transmissions that allow the GPS operation are hard to reach. For instance, commercial buildings, shopping malls, parking garages, as well as subways and tunnel systems are all possible applications for VLC-based indoor positioning systems. Additionally, once the VLC lamps are able to perform lighting at the same time as data transmission, it can simply occupy the installation of traditional single-function lamps. Other applications for VLC involve communication between appliances of a smart home or office. With increasing Internet of things, IoT-capable devices, connectivity through traditional radio waves might be subjected to interference. However, light bulbs with VLC capabilities would be able to transmit data and commands for such devices.

Machine vision systems

Machine vision systems often require bright and homogeneous illumination, so features of interest are easier to process. LEDs are often used. Barcode scanners are the most common example of machine vision applications, and many of those scanners use red LEDs instead of lasers. Optical computer mice use LEDs as a light source for the miniature camera within the mouse. LEDs are useful for machine vision because they provide a compact, reliable source of light. LED lamps can be turned on and off to suit the needs of the vision system, and the shape of the beam produced can be tailored to match the system's requirements.

Biological detection

The discovery of radiative recombination in Aluminum Gallium Nitride (AlGaN) alloys by United States Army Research Laboratory, U.S. Army Research Laboratory (ARL) led to the conceptualization of UV light emitting diodes (LEDs) to be incorporated in light induced fluorescence sensors used for biological agent detection. In 2004, the Edgewood Chemical Biological Center, Edgewood Chemical Biological Center (ECBC) initiated the effort to create a biological detector named TAC-BIO. The program capitalized on Semiconductor UV Optical Sources (SUVOS) developed by the DARPA, Defense Advanced Research Projects Agency (DARPA). UV induced fluorescence is one of the most robust techniques used for rapid real time detection of biological aerosols. The first UV sensors were lasers lacking in-field-use practicality. In order to address this, DARPA incorporated SUVOS technology to create a low cost, small, lightweight, low power device. The TAC-BIO detector's response time was one minute from when it sensed a biological agent. It was also demonstrated that the detector could be operated unattended indoors and outdoors for weeks at a time. Aerosolized biological particles will fluoresce and scatter light under a UV light beam. Observed fluorescence is dependent on the applied wavelength and the biochemical fluorophores within the biological agent. UV induced fluorescence offers a rapid, accurate, efficient and logistically practical way for biological agent detection. This is because the use of UV fluorescence is reagent less, or a process that does not require an added chemical to produce a reaction, with no consumables, or produces no chemical byproducts. Additionally, TAC-BIO can reliably discriminate between threat and non-threat aerosols. It was claimed to be sensitive enough to detect low concentrations, but not so sensitive that it would cause false positives. The particle counting algorithm used in the device converted raw data into information by counting the photon pulses per unit of time from the fluorescence and scattering detectors, and comparing the value to a set threshold. The original TAC-BIO was introduced in 2010, while the second generation TAC-BIO GEN II, was designed in 2015 to be more cost efficient as plastic parts were used. Its small, light-weight design allows it to be mounted to vehicles, robots, and unmanned aerial vehicles. The second generation device could also be utilized as an environmental detector to monitor air quality in hospitals, airplanes, or even in households to detect fungus and mold.

Other applications

The light from LEDs can be modulated very quickly so they are used extensively in optical fiber and free space optics communications. This includes remote controls, such as for television sets, where infrared LEDs are often used. Opto-isolators use an LED combined with a photodiode or phototransistor to provide a signal path with electrical isolation between two circuits. This is especially useful in medical equipment where the signals from a low-voltage sensor circuit (usually battery-powered) in contact with a living organism must be electrically isolated from any possible electrical failure in a recording or monitoring device operating at potentially dangerous voltages. An optoisolator also lets information be transferred between circuits that do not share a common ground potential. Many sensor systems rely on light as the signal source. LEDs are often ideal as a light source due to the requirements of the sensors. The Nintendo Wii's sensor bar uses infrared LEDs. Pulse oximeters use them for measuring oxygen saturation. Some flatbed scanners use arrays of RGB LEDs rather than the typical cold-cathode fluorescent lamp as the light source. Having independent control of three illuminated colors allows the scanner to calibrate itself for more accurate color balance, and there is no need for warm-up. Further, its sensors only need be monochromatic, since at any one time the page being scanned is only lit by one color of light. Since LEDs can also be used as photodiodes, they can be used for both photo emission and detection. This could be used, for example, in a touchscreen that registers reflected light from a finger or stylus. Many materials and biological systems are sensitive to, or dependent on, light. Grow lights use LEDs to increase photosynthesis in plants, and bacteria and viruses can be removed from water and other substances using UV LEDs for Sterilization (microbiology), sterilization. Deep UV LEDs, with a spectra range 247 nm to 386 nm, have other applications, such as water/air purification, surface disinfection, epoxy curing, free-space nonline-of-sight communication, high performance liquid chromatography, UV curing and printing, phototherapy, medical/ analytical instrumentation, and DNA absorption. LEDs have also been used as a medium-quality voltage reference in electronic circuits. The forward voltage drop (about 1.7 V for a red LED or 1.2V for an infrared) can be used instead of a Zener diode in low-voltage regulators. Red LEDs have the flattest I/V curve above the knee. Nitride-based LEDs have a fairly steep I/V curve and are useless for this purpose. Although LED forward voltage is far more current-dependent than a Zener diode, Zener diodes with breakdown voltages below 3 V are not widely available. The progressive miniaturization of low-voltage lighting technology, such as LEDs and OLEDs, suitable to incorporate into low-thickness materials has fostered experimentation in combining light sources and wall covering surfaces for interior walls in the form of LED wallpaper. File:LED screen behind Tsach Zimroni in Tel Aviv Israel.jpg, A large LED display behind a disc jockey File:LED Digital Display.jpg, Seven-segment display that can display four digits and points File:LED panel and plants.jpg, LED panel light source used in an experiment on plant growth. The findings of such experiments may be used to grow food in space on long duration missions.

Research and development

Key challenges

LEDs require optimized efficiency to hinge on ongoing improvements such as phosphor materials and quantum dots. The process of down-conversion (the method by which materials convert more-energetic photons to different, less energetic colors) also needs improvement. For example, the red phosphors that are used today are thermally sensitive and need to be improved in that aspect so that they do not color shift and experience efficiency drop-off with temperature. Red phosphors could also benefit from a narrower spectral width to emit more lumens and becoming more efficient at converting photons. In addition, work remains to be done in the realms of current efficiency droop, color shift, system reliability, light distribution, dimming, thermal management, and power supply performance.

Potential technology

Perovskite LEDs (PLEDs)

A new family of LEDs are based on the semiconductors called Perovskite (structure), perovskites. In 2018, less than four years after their discovery, the ability of perovskite LEDs (PLEDs) to produce light from electrons already rivaled those of the best performing OLEDs. They have a potential for cost-effectiveness as they can be processed from solution, a low-cost and low-tech method, which might allow perovskite-based devices that have large areas to be made with extremely low cost. Their efficiency is superior by eliminating non-radiative losses, in other words, elimination of Carrier generation and recombination, recombination pathways that do not produce photons; or by solving outcoupling problem (prevalent for thin-film LEDs) or balancing charge carrier injection to increase the External quantum efficiency, EQE (external quantum efficiency). The most up-to-date PLED devices have broken the performance barrier by shooting the EQE above 20%. In 2018, Cao et al. and Lin et al. independently published two papers on developing perovskite LEDs with EQE greater than 20%, which made these two papers a mile-stone in PLED development. Their device have similar planar structure, i.e. the active layer (perovskite) is sandwiched between two electrodes. To achieve a high EQE, they not only reduced non-radiative recombination, but also utilized their own, subtly different methods to improve the EQE. In the work of Cao ''et al.'' , researchers targeted the outcoupling problem, which is that the optical physics of thin-film LEDs causes the majority of light generated by the semiconductor to be trapped in the device. To achieve this goal, they demonstrated that solution-processed perovskites can spontaneously form submicrometre-scale crystal platelets, which can efficiently extract light from the device. These perovskites are formed via the introduction of amino acid additives into the perovskite Precursor (chemistry), precursor solutions. In addition, their method is able to passivate perovskite surface Crystallographic defects in diamond, defects and reduce nonradiative recombination. Therefore, by improving the light outcoupling and reducing nonradiative losses, Cao and his colleagues successfully achieved PLED with EQE up to 20.7%. In Lin and his colleague's work, however, they used a different approach to generate high EQE. Instead of modifying the microstructure of perovskite layer, they chose to adopt a new strategy for managing the compositional distribution in the device——an approach that simultaneously provides high luminescence and balanced charge injection. In other words, they still used flat emissive layer, but tried to optimize the balance of electrons and holes injected into the perovskite, so as to make the most efficient use of the charge carriers. Moreover, in the perovskite layer, the crystals are perfectly enclosed by MABr additive (where MA is CH3NH3). The MABr shell passivates the nonradiative defects that would otherwise be present perovskite crystals, resulting in reduction of the nonradiative recombination. Therefore, by balancing charge injection and decreasing nonradiative losses, Lin and his colleagues developed PLED with EQE up to 20.3%.

See also

* History of display technology * LED tattoo * Light-emitting electrochemical cell * List of LED failure modes * List of light sources * Photovoltaics * SMD LED module * Superluminescent diode * MicroLED * Solar lamp * Solid-state lighting * Thermal management of high-power LEDs * UV curing


Further reading


External links

Building a do-it-yourself LED

Color cycling LED in a single two pin package
* {{Authority control Light-emitting diodes, LED lamps Optical diodes Display technology Signage 20th-century inventions Japanese inventions