A light-emitting diode (LED) is a semiconductor device which works whenever a forward current is flowing through a semiconductor junction diode, each time an electron and a hole recombine; energy is released as a photon. The color of the light is related to the energy of the photon, which is in turn determined by the energy band gap of the semiconductor material. The light is not particularly bright, but in most LEDs it is monochromatic, occurring at a single wavelength.