Light Emitting Diode

Light Emitting Diode

Light Emitting Diode definition
Light Emitting Diode working
Light Emitting Diode circuit diagram
Light Emitting Diode applications

Good Morning everyone!
Today we will be learning about LED and its working.

Lets start with the topic

Light Emitting Diode 

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

    A PN junction can convert absorbed light energy into a proportional electric current. The same process is reversed herre. This phenomenon is generally called electroluminescence. Electroluminescene is the property of the material to converrt electric energy into light energy and later it radiates this light energy. 

Working Principle

The charge carriers recombine in a forward biased PN junction as the electrons cross from the N region and recombine with the holes existing in the P region. Free electrons are in the conduction band of energy levels, while holes are in the valence energy band. Thus the energy level of the holes is less than the electrons. Some portion of the energy must be dissipated to recombine the electrons and holes. This energy is emitted in the form of the heat and light.



Fig

The working of the LED depends on the quantum theory. The quantum theory states that when the energy of electrons decreases from the higher level to lower level, it emits energy in the form of photons. The energy of the photons is equal to the gap between the higher and lower level as shown in fig

 The LED is connected in the forward biased, which allows the current to flows in the forward direction. The flow of current is because of the movement of electrons in the opposite direction. The recombination shows that the electrons move from the conduction band to valence band and they emits electromagnetic energy in the form of photons. The energy of photons is equal to the gap between the valence and the conduction band. Color of light was determined by the band gap of semiconduction or material.

 Applications
  • There are used in remote control systems such TV or LCD remote.
  • Used in electronic calculators for showing the digital data.
  • Used in traffic signals for controlling the traffic crowds in cities.
  • Used in digital computer for displaying the computer data.
  • Used in digital watches and automotive heat lamps.

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