LIGHT EMITTING DIODES (LED) BY AARTHI.M (221710303001)

 WHAT IS LED?

It is a p-n junction diode that emits light when activated.When  suitable voltage  is being applied to the LED electrons are able to recombine with the electron holes within the device releasing energy
in the form of photons. This effect is called  electroluminescence and the  colour of the light is determined by the energy band gap of the semiconductor.The first typical LED was of low intensity and was limited to red.Modern LED are available across the visible,ultraviolet and infrared wavelengths,with very high brightness.



WORKING PRINCIPLE

The p-n junction diode can convert absorbed light energy into proportional electric current.The same process is reversed here. this process is called electroluminescence which can be defined as the emission of light from the semiconductor under the influence of an electric field.the charge carriers recombine in forward bias p-n junction as the electrons flow from the N region and recombine with the holes existing in the P region.   Free electrons are in the conduction band of energy levels,where holes are in the valence energy band.thus energy level of the holes is less than the energy level of electrons.some energy must be dissipated in order to recombine the  electrons with the holes.This energy is dissipated in the form of heat and light.

ADVANTAGES

• low energy consumption
• longer life time
• improved physical robustness
• smaller size
• faster switching
• environment friendly
• efficient

DIADVANTAGES

• costly
• correct voltage must be applied
• increase in temperature and age can change LED colour