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In 1961, experimenters Robert Biard and Gary Pittman working at Texas Instruments, found that Gallium Arsenide emitted infrared radiation when electric current was applied and received the patent for the infrared LED.
The first practical visible-spectrum (red) LED was developed in 1962 by Nick Holonyak Jr., while working at General Electric Company. Holonyak is seen as the "father of the light-emitting diode". 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 created the first high-brightness, high efficiency LEDs for optical fiber telecommunications by inventing new semiconductor materials specifically adapted to optical fiber transmission wavelengths.
LEDs remained mostly limited to indicator applications as they were not yet bright enough to function as usable lighting. This changed in 1994 when the first high-brightness blue LED was demonstrated by Shuji Nakamura of Nichia Corporation. The existence of blue LEDs and high efficiency LEDs quickly led to the development of the first white LED, which employed a phosphor coating to mix yellow (down-converted) light with blue to produce light that appears white.
The development of LED technology has caused their efficiency and light output to increase exponentially, with a doubling occurring about every 36 months since the 1960s.
In February 2008, Bilkent university in Turkey reported 300 lumens of visible light per watt luminous efficacy (not per electrical watt) and warm light by using nanocrystals. |
