LED stands for Light Emitting Diode. An LED is a solid state device that converts electric energy directly into monochromatic (single color) light. It is a "PN junction semiconductor diode" that emits light when operated in a forward biased direction. The basic LED structure consists of the die or light emitting semiconductor material, a lead frame where the die is actually placed, and the encapsulation epoxy which surrounds and protects the die.
LED's employ "cold" light, which means that most of the energy delivered is in the visible spectrum. LED's waste little energy in the form of heat. In comparison, most of the energy in an incandescent light source is in the infrared (non-visible) portion of the spectrum that results in a lot of heat.
In addition to producing cold light, LED's require much less power than existing lighting solutions, are small in size, resistant to vibration & shock, have a very fast "on-time" (less than 1 millisecond compared to 250 milliseconds for incandescent), have good color resolution, and present low or no shock hazard. The first commercially usable LED's were developed in the 1960's by combining three primary elements: Gallium, Arsenic, and Phosphorous (GaAsP) to obtain a red light source. As LED technology progressed through the 1970's, additional colors and wavelengths became available. The most common materials were GaP-green and red, GaAsP-orange or high efficiency red, and GaAsP-yellow; All of which are still utilized today. In the 1980's a new material was developed (Gallium, Aluminum, Arsenide (GaAlAs)) that provided superior performance with an increase in brightness of 10x over the previously available LED's.
Currently, white LED's are achieved in one of the following three methods:
- Red, Blue, Green (RGB) LED color mixing;
- Coating a Blue LED with Phosphor (typically Yttrium Aluminum Garnet – YAG) so that when energized photons strike the coating it will emit a mixture of wavelengths to produce a white color;
- Coating an Ultra Violet (UV) LED with Phosphor as above