LED or Light Emitting Diode is a PN junction diode, which is specially doped and made of special type of semiconductor, emits light when it is forward biased is called light emitting diode. In other words, a light-emitting diode (LED) is a two-lead semiconductor light source. It is a p–n junction diode, which emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons.
The forward bias Voltage-Current (V-I) curve and the output characteristics curve are shown in the figure above. The V-I curve is practically applicable to burglar alarms. The forward bias of approximately 1 volt is needed to give significant forward current. The second figure is used to represent a radiant power-forward current curve. The output power produced is very small and thus the efficiency in electrical-to-radiant energy conversion is very less.
The commercially used LED‘s have a typical voltage drop of 1.5 Volt to 2.5 Volt or current between 10 to 50 milliamperes. The exact voltage drop depends on the LED current, colour, tolerance, and so on.