Light Emitting Diode (LED)

                                                           Light Emitting Diode (LED) 

Diode 

•       A semiconductor device with two terminals typically allowing an electric current to flow in one direction, but blocks in the opposite direction. 

• The diode is formed by bringing two slightly different materials together to form a PN junction. 

Light Emitting diode 

• LED is a semiconductor light source that emits light when current flows through it. 

• LED convert electrical energy into light energy. 

  
  
  

LED Symbol 

The LED symbol is the standard symbol for a diode, with the addition of the two small arrows denoting the emission of light. 

Principle 

Energy is required to take an electron from valence band to conduction band, to generate electron hole pair. Conversely, energy is emitted when an electron and hole recombine. In semiconductors like GaAs (gallium Arsenide), GaP (gallium phosphide) the energy is emitted in the form of light.  

How Light emitting Diode work 

When the negative end of a circuit is hooked up to the N-type layer end the positive end is hooked up with P-type layer then electron and holes start moving. If you try to run current the other way, with the P-type side connected to the negative and of the circuit and the N-type side connected to the positive end, current will not flow. No current flows across the junction because the hole and the electron are each moving in the wrong direction. When current flows across a diode. Negative electrons move one way, and the positive holes move the other way. The whole exists at a lower energy level than the free electrons. Therefore, when a free electrons falls it losses energy. The energy is emitting in a form of a photons, which cause light. The color of the light is determined by the fall of the electron and hence energy level of the photon.