Light Emitting Diode (LED)

Light Emitting Diode

The LED is a PN-junction diode which emits light when an electric current passes through it in the forward direction.

The electron from the N-side and the hole from the P-side are combined and gives the energy in the form of heat and light. 

The LED is made of semiconductor material which is colourless, and the light is radiated through the junction of the diode.

Construction of LED

The semiconductor material used in LED is Gallium Arsenide (GaAs), Gallium Phosphide (GaP) or Gallium Arsenide Phosphide (GaAsP). Any of the above-mentioned compounds can be used for the construction of LED, but the colour of radiated light changes with the change in material. Below are some of the material and their respective colour of light which they emit. 

Working of LED

The electrons are majority carriers in N-type and holes are majority carriers in P-type. The electrons of N-type are in the conduction band and holes of P-type are in the valence band. The energy level of the Conduction band is higher than the energy level of the Valence band. Thus, if electrons tend to recombine with holes they have to lose some part of the energy to fall in lower energy band.

The electrons can lose their energy either in the form of heat or light. The electrons in Silicon and Germanium lose their energy in the form of heat. Thus, they are not used for LEDs as we want semiconductor in which electrons lose their energy in the form of light.

Thus, semiconductor compounds such as Gallium Phosphide (Gap), Gallium Arsenide (GaAs), Gallium Arsenide Phosphide (GaAsP) etc. emit light when electrons-holes recombine. The electrons in these compounds lose their energy by emission of photons.

If the semiconductor material is translucent, the light will be emitted from the junction as junction acts as the source of light. LED is operated in forward biased mode only. If it will operate in reverse biased it will get damage as it cannot with stand reverse voltage.

Advantages of LED

1. Temperature Range: It can be operated over a wide range of temperature ranging from 00C -700C

2. Low Power Consumption: They consume less power and they can be used even if the dc power supplied is low.

3. Better Controlling: The radiant power of LEDs is the function of the current flowing in it. Thus, the light intensity of LED can be controlled 

4. Economical and Reliable: LEDs are cheap and they possess a high degree of reliability.

5. Small Size and Portability

6. Higher Efficiency

Disadvantages of LED

  1. Over voltage or Overcurrent:The LEDs may get damaged when the current is increased beyond a certain limit.
  2. Overheating due to radiant power




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