Light Emitting Diode The LESD is basically a device which changes input electrical energy into output optical radiation in the visible or infrared position of spectrum depending on the semiconductor material used. LEDs have replaced incandesced lamp in many applications because of low voltage long life and fast on off switching. He materials used in manufacturing the LEDs are 1. Gallium Arsenide Phosphide (GaAsP): It provides either red light or yellow light. 2. Gallium Phosphide (GaP): It provides red or green light. 3. Gallium Arsenide (GaAs): It provides infrared radiation Principle: When a P-N junction forward biased, charge carrier recombination take place at a junction as electron cross from the n- side and combine with holes on the p- side. Free electrons are in the conduction band of energy level while holes are in the valence band. Therefore electronics are at place ...