A light emitting diode or LED is a semiconductor device that emits incoherent narrow spectrum light when electrically biased in the forward direction.
This effect is a form of electroluminescence. The color of the emitted light depends on the composition and condition of the semiconducting material used, and can be near ultraviolet, visible or infrared. Like a normal diode, LED consists of a chip of semiconducting material impregnated, or doped, with impurities to create a structure called a p-n junction. As in other diodes, current flows easily from the p-side, or anode to the n-side, or cathode, but not in the reverse direction. Charge carriers flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon.