A diode is a two terminal electric component that enables the flow of charge in only one direction. It can be a vacuüm tube diode or a semiconductor diode. A semiconductor diode is a crystalline piece of semiconductor material with the p-n junction acting as two electrical terminals.
A semiconductor conducts electricity between a metal and an insulator. A light emitting diode is a semiconductor chip doped with certain impurities to create p-n junction. The term p-n stand for positive (anode) and negative (cathode). When a small electric current flows, charge carriers namely, electron and holes flow into the junction well from electrodes having different voltage. When an electron meets a hole, it falls into a lower energy level. The excess energy escapes in the form of an illuminating photon. A photon is a particle representing a quantum of light. This is known as electroluminescence.
The color of this light depends on the amount of excess 2CL2FM released. This is known as band gap energy. Depending upon the band gap, we get light from the near infrared to near ultraviolet frequencies. Band energy depends upon the semiconductor material. For instance, Gallium Arsenide gives infrared light. Indium Gallium Nitride offers green light. Zinc Selenide emits blue color.
White light LED lamp consists of several diodes. These diodes individually emit the three primary colors namely, blue, green, and red. A phosphor material is also used to convert the ultraviolet emission into a white light.
A microsphere shaped semiconductor gives the largest output of light. The emanating light from inside the center of the semiconductor will be perpendicular to the entire surface area of the microsphere. There will be no internal reflection. The next best option is a hemispherical semiconductor. The flat back surface serves as a reflecting mirror to back scattered photons.
Semiconductor chips are commonly encapsulated in molded plastic shells. This makes mounting a circuit easier. It gives support to fragile electric wires. These plastic shells have an intermediate refractive index with respect to the semiconductor and the open air.
The LED operates at a very low current. It needs 20 mA current. Its configuration makes it a low temperature device. There is hardly any unforced wear and tear. Therefore, it has a very long life cycle. It is between 25,000 to 100,000 hours. However, high power LED may have a shorter life cycle as these are subjected to high junction temperature and current densities.