LEDs are p-n junction diodes which can emit radiation in the visible range (370nm to 770nm) under forward biased condition.
In a p-n junction electrons from n side diffuses to p side and holes from p side moves towards n side forming a depletion region. So no mobile charges present in the depletion region.When sufficient voltage is applied movement of electrons across junction takeplace. These electrons when recombined with holes , a quantum of electromagnetic energy is emitted in the form of photon of light with frequency charateristic of semiconductor material ( generally GaAsP , GaP).
Characteristics:
1. These give adequate power.
2. These give low noise.
3. LEDs are compatible with optical fibre.
4. The light from LED can be varied or modulated by altering applied voltage or current which is helpful in transmitting information.
Applications:
1. They can be used as cheap source of light.
2. In optical fibre applications.
3. They can be used as sensor as in case of optical mouse of computer.
