Operation of LED[Light emitting diode]

1. The increasing use of digital displays in calculators, watches, and all forms of instrumentation has contributes to the current extensive interest in structures that will emit light when properly biased.
2. The two types in common use today to perform this function are the light-emitting diode (LED) and the liquid-crystal display (LCD).
3. As the name implies, the light-emitting diode (LED) is a diode that will give off visible light when it is energized. In any forward-biased p-n junction there is, within the structure and primarily close to the junction, a recombination of holes and electrons.
4. This recombination requires that the energy possessed by the unbound free electrons be transferred to another state. In all semiconductor p-n junctions some of this energy will be given off as heat and some in the form of photons.
5. LED displays are available today in many different sizes and shapes. The light emitting region is available in tengths from 0.1 to 1 inch. By applying a forward-bias to the proper p-type material segment, any number from 0 to 9 can be displayed.
6. LEDs are presently available in red, green, yellow, orange, and white, and white with blue soon to be commercially available. LEDs operate at voltage levels from 1.7V to 3.3V, which makes them completely compatible with solid-state circuits.
7. They have a fast response time (nano seconds) and offer good contrast ratios for visibility. The power requirement is typically from 10 to 150mW with a lifetime of 1,00,000 hours.