It is heavily dopped PN junction diode which converts electrical energy into light energy. This diode emits spontaneous radiation under forward biasing.
Its symbol is-
When PN junction is forward biased, electrons and holes move toward opposite sides of the junction through it. Therefore, there are excess minority careers on the either side of the junction boundary, which recombines with majority careers near the junction.
On recommendation of electron and holes the energy is given out in the form of heat and light.
V-I Characteristics Of LED
From graph it is clear that the threshold voltages are much higher and slightly different for each colour. The colour of light emitted by a given LED, depends on its band gap energy. The photon emitted by an LED is of energy equal to or slightly less than the band gap energy.
LEDs Advantages Over Incandescent Low Power Lamps
It has the following advantages over conventional incandescent low power lamps.
(I) Fast action and no warm up time required.
(II) The bandwidth of emitted light is from 100 to 500 angstrom. So, it is nearly (not exactly) mono chromatic.
(III) Long life and ruggedness.
(IV) Low operational voltage and less power consumed.
(V) Fast ON-OFF switching capability.