Light-emitting diode (LED) is an electric component that emits light when connected to direct current. It works on electroluminescent principle and can emit light in visible spectrum as well as in infrared (IR) and ultraviolet (UV).
Historical course
- At early 20th century, it was noticed for the first time that when a potential of 10volts is applied to carborundum (silicon carbide) crystal, it emits yellowish light. For decades no progress was made for different reasons.
- Mid of 20th century, it was observed that some simple diodes emit infrared light when connected to a current. Later on, it was found that gallium-arsenide diode emits infrared light every time it is connected to current.
- In 1960's, a light-emitting diode was developed for the very first time, that emitted light in the visible part of the frequency range. It was a red LED.
- In 1970's, the first yellow LED and a brighter red LED was invented.
- The first blue LED was made at late 70's but it was too expensive for commercial use until mid 90's.
- Light emitting diodes are now available in one or in more colors.
At first, LED were very expensive. By using innovative methods of packaging and a planar process of chip production, LED became a commercial product with variety of uses.
LED with visible light is used as a replacement for incandescent and neon lights, as elements in seven-segment displays, in large RGB screen displays and other visual signals, in calculators, watches and in flashlights. Infrared LEDs are used in units for remote control in TVs, DVDs and other places that need wireless control.
