A light-emitting diode (LED) is a diode that gives off visible light when forward biased.
Light-emitting diodes are not made from silicon or germanium but are made by using elements like gallium, phosphorus and arsenic. By varying the quantities of these elements, it is possible to produce light of different wavelengths with colors that include red, green, yellow and blue.
For example, when a LED is manufactured using gallium arsenide, it will produce red light. If the LED is made with gallium phosphide, it will produce a green light.
Working Theory of LED
The schematic symbol for a LED is shown in the above figure. The arrows are shown as pointing away from the diode, indicating that light is being emitted by the device when forward biased.
Although LEDs are available in several colours (red, green, yellow and orange are the most common), the schematic symbol is the same for all LEDs. There is nothing in the symbol to indicate the colour of a particular LED.
This is a graph between radiated light and the forward current of the LED. It is clear from the graph that the intensity of radiated light is directly proportional to the forward current of LED.