LED: Light Emitting Diode


It is heavily dopped PN junction diode which converts electrical energy into light energy. This diode emits spontaneous radiation under forward biasing.

Its symbol is-

LED Symbol
LED Symbol


When PN junction is forward biased, electrons and holes move toward opposite sides of the junction through it. Therefore, there are excess minority careers on the either side of the junction boundary, which recombines with majority careers near the junction.

On recommendation of electron and holes the energy is given out in the form of heat and light.

Working Of LED
Working Of LED
Working Of Light Emitting Diode
Working Of Light Emitting Diode

V-I Characteristics Of LED

From graph it is clear that the threshold voltages are much higher and slightly different for each colour. The colour of light emitted by a given LED, depends on its band gap energy. The photon emitted by an LED is of energy equal to or slightly less than the band gap energy.

V-I Characteristics Of LED
V-I Characteristics Of LED

LEDs Advantages Over Incandescent Low Power Lamps

It has the following advantages over conventional incandescent low power lamps.

(I) Fast action and no warm up time required.

(II) The bandwidth of emitted light is from 100 to 500 angstrom. So, it is nearly (not exactly) mono chromatic.

(III) Long life and ruggedness.

(IV) Low operational voltage and less power consumed.

(V) Fast ON-OFF switching capability.

Also Read: CBSE Class 12 Physics Chapter-14 (Semiconductor and Electronic Devices) All Topics

NCERT Class 12 Physics Chapter-1 Electric Charges And Fields Notes

NCERT Class 12 Physics Chapter-2 Electrostatic Potential And Capacitance Notes

NCERT Class 12 Physics Chapter-3 Current Electricity Notes

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