LED is short for light-emitting diode and works by running an electrical current through a semiconductor material, typically aluminum-gallium-arsenide, into the junction of a diode. Phosphor is added to the diode to filter the light output and create a more pure color.
Electroluminescence, the phenomenon of a material emitting light when electricity is passed through it, was first discovered in 1907 by H. J. Round. Gary Pittman and James R. Baird discovered the light-emitting diode in 1961. The first LED emitted infrared light and was used by Texas Instruments.
Amber, red, green and blue are common colors of LEDs. Since white light is not possible to produce using a single LED, a mixture of colored LEDs are used to generate the white light used in homes and offices. Colored LEDs are commonly used as signal or indicator lights, like a power button on a computer.
Different semiconductor materials produce different colors of light. Gallium arsenide produces red and infrared light, gallium nitride produces a bright blue light, and aluminum gallium phosphide produces green light. Orange and blue are also produced with a single semiconductor material, but violet, purple and pink are produced using layers of LED light and phosphors to tint the colors. Ultraviolet light is produced by diamond, boron nitride or aluminum nitride.