A light-emitting diode (LED) is a semiconductor light source that emits light when current flows through it. LEDs combine a P-type semiconductor with an N-type semiconductor. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light is determined by the energy required for electrons to cross the bandgap of the semiconductor. The applications of LEDs are to illuminate objects, places and indications.