A diode which are given light when it is forward bias is called LED. Led is the abbreviation of light emitting diode. Silicon or germanium are not used to made led. The other elements like as gallium and arsenic are used to made this type of diode. To produce different lights like as red, blue, green or yellow with different wavelengths, it is possible to varying the quantities of these elements which are used to made this type of diode. For example red light diode are manufactured by using gallium arsenide. Same as this method gallium phosphide are used to manufactured green colour led.
When led is forward bias the electrons from n-type material are forward to p-type material by cross the pn-junction and recombine with holes in p-type material. Recall these electron are in conduction band and holes are in valence band. After recall process the electron are release energy in the form of heat and light. If we used silicon or germanium material in led the result of these types material are just given up heat. However we used gallium types material in which produce visible light.
The modern world led change the concept of light. There are some advantages of led are.
1. Its operate at low voltages.
2. Its have a long life as compare to other light.
3. Its starting and closing is very fast.
Thanks.........for regard yasir ali