A light-emitting diode

Nov 22nd, 2011 | Posted by | Filed under LED Light

A light-emitting diode (LED) is a semiconductor light.[2] LEDs are used as indicator lamps in numerous devices and are increasingly used in other lighting. Introduced as being a practical electronic component in 1962,[3] early LEDs emitted low-intensity red light, but modern versions can be found across the visible, ultraviolet and infrared wavelengths, with very high brightness.

When a light-emitting diode is forward biased (started), electrons are able to recombine with electron holes while in the device, releasing energy as photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. LEDs are often small in area (lower than 1 mm2), and integrated optical components enables you to shape its radiation pattern.[4] LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, and faster switching. LEDs powerful enough for room lighting are relatively expensive and require more precise current and warmth management than compact fluorescent lamp sources of comparable output.

Light-emitting diodes are used in applications as diverse as replacements for aviation lighting, automotive lighting (particularly brake lamps, turn signals and indicators) plus in traffic signals. LEDs have allowed new text, video displays, and sensors for being developed, while their high switching rates are usually useful in advanced communications technology. Infrared LEDs may also be used in the remote control units for many commercial products including televisions, DVD players, as well as other domestic appliances.
Electroluminescence as a phenomenon was discovered in 1907 by the British experimenter H. J. Round of Marconi Labs, using a crystal of silicon carbide and also a cat’s-whisker detector.[5][6] Russian Oleg Vladimirovich Losev reported development of the first LED in 1927.[7][8] His research was distributed in Russian, German and British scientific journals, but no practical use was made of the discovery for several decades.[9][10] Rubin Braunstein of the Radio Corporation of America reported on infrared emission from gallium arsenide (GaAs) as well as other semiconductor alloys in 1955.[11] Braunstein observed infrared emission generated by simple diode structures using gallium antimonide (GaSb), GaAs, indium phosphide (InP), and silicon-germanium (SiGe) alloys at room temperature as well as at 77 kelvin.

In 1961, American experimenters Robert Biard and Gary Pittman working at Texas Instruments,[12] found out that GaAs emitted infrared radiation when household current was applied and received the patent for your infrared LED.

The first practical visible-spectrum (red) LED was made in 1962 by Nick Holonyak Jr., while working at Whirlpool Company.[3] Holonyak is seen as the “father of the light-emitting diode”.[13] M. George Craford,[14] a former graduate student of Holonyak, invented the initial yellow LED and improved the brightness of red and red-orange LEDs by the factor of ten in 1972.[15] In 1976, T.P. Pearsall come up with first high-brightness, high efficiency LEDs for optical fiber telecommunications by inventing new semiconductor materials specifically adapted to optical fiber transmission wavelengths.[16]

Until 1968, visible and infrared LEDs were extremely costly, around the order of US $200 per unit, and for that reason had little practical use.[17] The Monsanto Company was the initial organization to mass-produce visible LEDs, using gallium arsenide phosphide in 1968 to provide red LEDs suitable for indicators.[17] Horsepower (HP) introduced LEDs in 1968, initially using GaAsP provided by Monsanto. The technology proved to have major purposes of alphanumeric displays and was integrated into HP’s early handheld calculators. Within the 1970s commercially successful LED devices at under five cents each were that is generated by Fairchild Optoelectronics. These devices employed compound semiconductor chips fabricated while using the planar process invented by Dr. Jean Hoerni at Fairchild Semiconductor.[18] The combination of planar processing for chip fabrication and innovative packaging methods enabled the team at Fairchild led by optoelectronics pioneer Thomas Brandt to offer the needed cost reductions. These methods continue to be used by LED producers.[19]

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