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

Hint: The concept and working principle of p-n junction has been used. We see the consequence when forward bias is applied to a p-n junction diode. The energy emitted during recombination is in the form of light in an LED. LED is preferred over normal lamps because of its numerous advantages.

Complete answer:
When a forward junction is applied to a p-n junction diode, the majority charge carriers i.e. electrons from n-region and holes from p-region cross the junction. An electron from n-region crosses the barrier and reaches p-region. When electrons reach the p-region, they recombine with holes and recombination takes place.
When electrons recombine with hole it radiates energy. The energy emitted is in the form of heat. In light emitting diodes this same process happens but the emitted energy is in the form of light or say photons.
In traffic signals, television etc we can use LED over incandescent lamps.
We prefer LED over incandescent lamp due to following reasons:
1. LEDs consume less power than incandescent lamps.
2. Low maintenance required for LED.
3. The lifespan of an LED is much better than an ordinary lamp.
4. LEDs are compatible as they are lightweight and small in size.
5. LED’s don’t have issues with frequent switching as that of ordinary lamps.

Note:
LED stands for light emitting diode. LED is a light source. It emits light when current flows through it. On applying forward bias recombination of electrons and holes take place. This releases energy in the form of light. There are different applications of LED such as night lighting, in electrical devices, motorcycles, cars etc.
Incandescent lamps are electric lights which have a filament wire. Current is supplied to the filament. The filament wire glows when heated. Incandescent lamps can be used for night lamps, table lamps etc.