It is a kind of semiconductor electronic element that can emit light through a composite light source composed of trivalent and pentavalent elements. The electronic device, which appeared in 1962, emits only low-light red light in its early days and was used as an indicator light after HP bought the patent. And later developed other monochromatic versions. Today, they can emit light in visible, infrared and ultraviolet light, and their luminosity has increased to a very high level. With the emergence of white light emitting diode, the use has been from the initial indicator light and display board and other indicators, gradually developed to the recent lighting use.
A light-emitting diode (LED) that conducts electricity in only one direction is called forward bias. When an electric current flows through it, electrons and holes combine in the diode to emit a monochromatic light, called electroluminescence. The wavelength and color of the light depends on the type of semiconductor used and the element added intentionally. It has the advantages of high efficiency, long life, not easy to be damaged, fast reaction speed and higher reliability than traditional light source. The luminous efficiency of white LED has been improved in recent years. The cost per thousand lumens, also due to a large amount of capital investment has brought the price down, but the cost is still much higher than other traditional lighting. Nevertheless, in recent years it has been increasingly used for lighting purposes.