Light Emitting Diode (LED) is a forward biased PN junctions which emits visible lights when energized. It emits low light when reverse biased and if operated in the reverse direction, the LED will be quickly destroyed.
The construction of a light emitting diode is very different from that of a normal signal diode. The PN junction of an LED is surrounded by a transparent, hard plastic epoxy resign hemispherical shaped shell or body which protects the LED from both vibration and shock. Surprisingly, an LED junction does not actually emit that much light so the epoxy resin body is constructed in such a way that the photons of light emitted by the junction are reflected away from the surrounding substrate base to which the diode is attached and are focused upwards through the domed top of the LED, which itself acts like a lens concentrating the amount of light. This is why the emitted light appears to be brightest at the top of the LED.
Application of LED:-
1. LED are used in burglar alarm system.
2. LED are used for the solid state video display which are rapidly replacing Cathode Ray Tube(CRT).
3. LED are used for numerical displays in pocket calculators.
4. LED are used for displaying alpha-numeric or supplying input powers to lasers for entering information into optical computer memories.