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Light emitting diodes (LEDs) are semiconductor devices which provide visible or infrared light when an electric current is applied. The light emitted by the LED is monochromatic in nature, i.e., occurs at single wavelength. The wavelength of the LED light output can vary between 700 and 400 nm. In some cases, LEDs are capable of emitting infrared light at a wavelength of 830 nm or more.
Basic Principle
A typical LED consists of two elements made up of semiconductor materials, namely p-type semiconductors and N-type semiconductors. Both the elements are in close contact with each other to form a P-N junction. Like other diodes, electric current easily passes to the N-side region or cathode from the P-side region or anode. As a result, charge carriers such as electrons and holes are transmitted via the junction at varying voltages. When an electron interacts with a hole, it falls into lower energy level thereby releasing energy in the form of photons. Thus, the wavelength of light emitted by the LED depends on the energy of band gap of the semiconductor materials.
Applications
Some of the major applications of LEDs include the following:
- Signs and indicator lamps
- Lighting systems
- Remote controls
- Optocouplers and optoisolators
- Medical applications
Sources and Further Reading