by Tenebris

Created on: June 17, 2008

The light-emitting diode (LED) is the emerging core technology of modern lighting, gradually superceding such earlier light-generating technologies as the incandescent light bulb and the fluorescent tube. Although LED technology has actually been around for nearly a hundred years, it has only emerged into popular awareness within the last decade. With the growing energy and environmental awareness of the twenty-first century, LED technology is finally starting to come into its own.

LED technology was first invented in the early 1920s by Henry Round (of Marconi Labs) and Oleg Losev, working independently. However, Losev's research saw limited circulation, primarily in the Soviet Union and Germany, and was finally buried under the tide of world events. In 1962 the first visible-spectrum LED was created by Nick Holonyak, then with the General Electric Company, who is considered the father of the light-emitting diode. However, low-powered LEDs emitting longer wavelengths such as reds and oranges proved considerably easier to develop. A very low power blue LED was developed by Jacques Pankove (of RCA Laboratories) in 1971; but it was not until 1995 that Shuji Nakamura (of Nichia Corporation) was able to demonstrate the first high-brightness blue LED, for which he was awarded the 2006 Millennium Technology Prize. Building on this research, an LED which produced white light, the holy grail of artificial light, was created by Alberto Barbieri by using a YAG' phosphor to emit blue light mixed with a down-shifted yellow. Although the light thus produced is considered 'white', this was actually the first bicolour LED.

Light is produced by an LED directly in response to an electrical current passing from the anode (sometimes called the p-side) to the cathode (sometimes called the n-side), an optical phenomenon known as electroluminescence. Unlike the incandescent light bulb, an LED does not produce light as a byproduct of heat, which makes the LED much more electrically efficient and also makes it much faster to turn on and off. In fact, LEDs scarcely produce any heat at all: a highly useful feature in enclosed spaces and increasingly hot climes. However, LED degradation and failure is also accelerated by exposure to heat, both operational and external.

Because an LED generates light directly, it can potentially be made of any semiconducting material. (It is the impurities in this material, called phosphors, which determine the band-gap energy of the p-n junction, and thus

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