In the planar LED, The reflection loss is more because most of the emitted light strikes the material interface at an angle greater than the critical angle. Therefore they are totally internally reflected and will not come out of the interface, thus the light is lost. This loss of light due to internal reflection can be minimized by two ways.
By making the ‘p’ material in the shape of a hemispherical dome. the angle at which the light strikes the interface can be made less than the critical angle and hence he light will not be lost by the total internal reflection.
By covering he p-n junction by a plastic medium of higher refractive index in the shape of hemispherical dome, total internal reflection can be reduced. This LED is used for commercial purpose. Hence, usually the dome shaped hemispherical LED is preferred than planar LED’s.
Advantages:
They are smaller in size.
Its cost is very low.
It has long life time.
LED’s are available in different colours at low cost.
It operates even at very low voltage.
Response time of LED is very fast in the order of secs.
Its intensity can be controlled easily.
It can be operated at a wide range of temperature .
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