LED (light emitting diode)
In a PN junction electrons cross from N-side and recombine with holes on the P side free electrons in the conductions band of energy level while holes in the valence bond. this electrons have a higher energy level than the holes. During the recombination the same energy is given up in the form of heat and light. If the semiconductor material is transistor translucent the light will be emitted and the junction becomes a light source. such a diode is called a light emitting diode.
The materials used in the PN junction are gallium arsenide, gallium arsenide phosphide or gallium phosphate.
Led lights are used in the panel indicator of electronic devices like UPS and COMPUTER, led lights are small semiconductor devices which emit light when a small forward current is applied to them.
when using LED light one need to add high value current limiting resistor( 1k) in series. LED'S available in day white, warm white, red ,green, yellow and pink colours.
When PC power switch is pressed once then SYSTEM turns ON and green LED get ON. POWER TURNS OFF by repressing this power switch and green led also turns off. power indicator is made on in that condition when power is made ON. power indicator displays the operating condition after turning ON
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