Q-27. With the help of a diagram, show the biasing of a light emitting diode (LED Geeste
advantages over conventional incandescent lamps.
Answers
The biasing of LED is forward bias which is explained as follow:-
LED is light emitting diode which is heavily doped forward biased p-n junction which convert electric energy into optical energy.The shorter lead responds to n or cathode side while longer lead corresponds to p or cathode side.The junction is made up of gallium arsenide.
When it is forward biased light photons are emitted from non metallised surface of n region to p region and holes from p to n region .Near junction concentration of minority carrier increases .On either side the excess minority carriers combine with majority carriers.
On recombination energy is released in form of photons.Photons with energy equal or lightly less than band gap are emitted.As current increases in forward bias intensity of light increases and reaches maximum and further increase in current decreases the light intensity.
Advantages over conventional incandescent lamps are as follow:--
- Low operational voltage and less power consumption.
- Fast action and no warm up time is required.
- Long life and fast ON/OFF switching capability.
- Bandwidth of emitted light is 100 to 500 angstrom that is light is monochromatic in nature.
