Question

In what respect is an LED different from an ordinary PN - junction diode? Where should we prefer LEDs over ordinary incandescent lamps? Why?

Answer 1

When a P-N junction diode is for ward-biased the potential barrier is lowered. The majority carriers start crossing the junction. The conduction band electrons from the N region cross the barrier and enter the P region. Immediately on entering the P region each electron falls into a hole and recombination takes place.
Each recombination radiates energy in an ordinary diode (power diode or signal diode). The radiated energy is in the form of heat. In the light emitting diode (LED), the radiated energy is in the form of light (or photons):
LEDs are used in traffic signals, TV etc.
LEDs have number of advantages over ordinary incandescent lamps. They work on low voltage (1 or 2 V) and currents (5 to 10 mA) and thus consume less power. They require no heating, no warm-up time, and hence they are very fast in action. They are small in size and light in weight. They are not affected by mechanical vibrations, and have long life (more than 20 years).