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The History of LED

So Where did this technology come from?

The History of LED.

The first known report of light-emitting solid state diode was made in 1907 by British experimenter H J Round of Marconi Labs. Russian Oleg Vladimirovech Losev independently created the first LED in mid 1920s. His research was ignored and no practical use was made for several decades. In 1962 the first practical visible spectrum (red) LED was developed by Nick Holonyak of the General Electric Company and later with the University of Illinois developed the technology and are seen as "the father of the light emitting diode" In 1972 Holonyak's former graduate student invented the first yellow LED and 10x brighter red and red-orange LEDS. Later Japanese Shuji Nakamura of the Nichia Corporation demonstrated the first high-brightness blue LED. The existence of the blue LED and high effficiency quickly carried to the first white LED (appears to be white) He was awarded the 2006 Milennium Tchnology Prize for his invention.

Practical use

The first commercial LEDS were used as replacements for incandescent indicators and in seven-segment displays first in expensive laboratory and electronics test equipment, then later in appliances such as Radios, Telephones, Calculators, and even Watches. These red Leds were bright enough for use as indicators but not bright enough to illuminate an area. Later, other colours appeared and as the LED materials technology became more advanced the Light Output was increased while maintaining the efficiency and reliability causing LEDs to become bright enough for illumination.

Conventional LEDS are made from a variety of inorganic semiconductor materials producing the following colours.

Aluminium gallium aresenide (AlGaAs) =red and infrared.

Aluminium gallium phosphide (AlGaP) =green

Aluminium gallium indium phospide (AlGaInP) = high brightness orange-red, yellow and green,

Gallium arsenide phosphide (GaAsP) =red, orange-red, orange and yellow.

Gallium phosphide (GaP) = red, yellow and green.

Gallium nitride (GaN) = green, pure green (or emerald green) and blue also white (if it has an AlGaN Quantum Barrier)

Indium gallium nitride (InGaN)-450-470nm = near ultraviolet, bluish green and blue.

Silicon carbide (SiC) as substrate = blue.

Silicon (Si) as substrate = blue (under development)

Sapphire (Al2O3) as substrate = blue

Zinc selenide (ZnSe) = blue.

Diamond (C) =ultraviolet

Aluminium nitride (AIN), Aluminium gallium nitride (AIGaN), Aluminium gallium indium nitride (AIGaInN) = near to far ultraviolet

With this wide variety of colours, arrays of multicolour LEDS can be designed to produce unconventional colour patterns.

White light LEDs

There are two ways of producing high intensity white light using LEDs.

1. Use individual LEDS that emit three primary colours: red, green and blue and then mix all the colours to produce white light.

or

2. Use phosphor material to convert monochromatic light froma a blue or UV LED to broad spectrum white light.

Advantages of using LEDs