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LED - Light Emitting Diode

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Light Emitting Diodes

Light Emitting Diodes

Getty Images Janet Kimber
An LED, which stand for light emitting diode, is a semiconductor diode that glows when a voltage is applied and they are used everywhere in your electronics, new types of lighting, and digital television monitors.

How An LED Works

Let's compare how the light emitting diode works versus the older incandescent lightbulb. The incandescent lightbulb works by running electricity through a filament that is inside the glass bulb. The filament heats up and glows, and that creates the light, however, it also creates a lot of heat. The incandescent lightbulb loses about 98% of its energy producing heat making it quite inefficient.

LEDs are part of a new family of lighting technologies called solid-state lighting and in a well-designed product; LEDs are basically cool to the touch. Instead of one lightbulb, in an LED lamp there will be a multiple of small light emitting diodes.

LEDs are based on the effect of electroluminescence, that certain materials emit light when electricity is applied. LEDs have no filament that heats up, instead they are illuminated by the movement of electrons in a semiconductor material, usually aluminum-gallium-arsenide (AlGaAs). The light emits from the p-n junction of the diode.

Exactly how an LED works is a very complex subject, here are four excellent tutorials that explain this process in detail:

Background

Electroluminescence, the natural phenomena upon which LED technology is built was discovered in 1907 by British radio researcher and assistant to Guglielmo Marconi, Henry Joseph Round, while experimenting with silicon carbide and a cats whisker.

During the 1920s, Russian radio researcher Oleg Vladimirovich Losev was studying the phenomena of electroluminescence in the diodes used in radio sets. In 1927, he published a paper called Luminous carborundum [silicon carbide] detector and detection with crystals about his research, and while no practical LED was created at that time based on his work, his research did influence future inventors.

Years later in 1961, Robert Biard and Gary Pittman invented and patented an infrared LED for Texas instruments. This was the first LED, however, being infrared it was beyond the visible light spectrum. Humans can not see infrared light. Ironically, Baird and Pittman only accidentally invented a light emitting diode while the pair were actually attempting to invent a laser diode.

Visible LEDs

In 1962, Nick Holonyack, a consulting engineer for General Electric Company, invented the first visible light LED. It was a red LED and Holonyack had used gallium arsenide phosphide as a substrate for the diode.

Holonyack has earned the honor of being called the "Father of the light emitting diode" for his contribution to the technology. He also holds 41 patents and his other inventions include the laser diode and the first light dimmer. (Another interesting fact about Holonyack was that he was once the student of John Bardeen, the co-inventor of the transistor.)

In 1972, electrical engineer, M George Craford invented the first yellow colored LED for the Monsanto Company using gallium arsenide phosphide in the diode. Craford also invented a red LED that was 10 times brighter than Holonyack's.

It should be noted that the Monsanto Company was the first to mass-produce visible LEDs. In 1968, Monsanto produced red LEDs used as indicators. But it was not until the 1970s that LEDs became popular, when Fairchild Optoelectronics began producing low-cost LED devices (less than five cents each) for manufacturers.

In 1976, Thomas P. Pearsall invented a high-efficiency and extremely bright LED for use in fiber optics and fiber telecommunications. Pearsall invented new semiconductor materials optimized for optical fiber transmission wavelengths.

In 1994, Shuji Nakamura invented the first blue LED using gallium nitride.

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