2. CONTENT
1.What is light emitting diode(led) ?
2.Principle
3.Symbolic diagram of LED
4.Advantages
5.Applications
3. What is light emitting diode(led) ?
• A p-n junction diode which emits light on forward biasing is
know as light emitting diode(led).
• The light emitting diodes emit either visible light or invisible
infrared light when forward biased.
• The led which emit invisible infrared light are used for remote
controls.
• Incandescent bulb by Thomas Edison(1879) and invented by
Nick Holonyak
4. • Principle
• If the led is forward biased then the free electron from
n-type material cross the junction and recombine with the
holes in p-type material. The free electrons are in conduction
band at higher energy level than the holes in the valence band.
When free electrons recombine with the holes , energy is
released in the form of heat and light. In materials like gallium
phosphide and gallium arsenide, the number of photons of
light energy is enough to produce intensive visible light.
• If the led is made with gallium phosphide then it will emit
green light.
