Question

(1) Describe the working of Light Emitting diodes (LEDs).
(2) Which semiconductors are preferred to make LEDs and why?
(3) Give two advantages of using LEDs over conventional incandescent low power lamps.

Answer 1

Hint:A light emitting diode is a semiconductor device which propagates or throws light around, for the device to throw light around current must flow through it. Earlier the LED’s could only produce red colour but nowadays they can produce a variety of colours.

Complete step by step solution:
LED works on the principle of a Quantum Theory. The quantum theory states that when the energy of electrons which are present in the semiconductor decreases from the higher level to a lower level, it emits energy which is in the form of photons. The larger the gap the more energy the photons will have. The recombination of the electrons shows that they move from conduction band to valence band and emits an energy which is electromagnetic in nature and is in the form of photons.
The preferred semiconductors that are used in making the LED are Gallium Arsenide, Gallium phosphide or the combination of the two Gallium arsenide phosphide. The different materials of the semiconductors and doped with different impurities results in different colours from LED.
LED’s are highly energy efficient and use 90% less energy than the lower power incandescent bulbs. It dramatically decreases power costs and also the LED’s are more luminous than the bulbs because most of the power of the bulb goes waste as heat.

Note:LEDs are one of the most ubiquitous products today thanks to their power efficiency, cost reduction, easy maintenance etc. It was only recently that the elusive blue LED was made. Scientists have developed a technique for producing multiple colours from a single LED.