LED (Light Emitting Diode), light-emitting diode, is a solid state semiconductor devices, which can be diectly converted into electricity to light. LED is the heart of a semiconductor chip, the chip is attached to one end of a stent, is the negative side, the other end of the power of the cathode, the entire chip package to be epoxy resin. Semiconductor chip is composed of two parts, part of the P-type semiconductor, it inside the hole-dominated, the other side is the N-type semiconductor, here is mainly electronic. But linking the two semiconductors, among them the formation of a "PN junction". When the current throgh the wires role in this chip, will be pushing e-P, P zone in the hole with electronic composite, and then to be issued in the form of photon energy, and this is the principle of LED luminescence. The wave length of light that is the color of light, is formed by the PN unction of the decisions of the material. With the appearance of the White Light-Emitting Diodes, the LED also developed to be used for lighting. It is a new type of light source in the 21st century with advantages of high efficiency, long-life span and invulnerability which can not be compaed with the traditional light sources. When being pressured with positive voltage, the LED can emit single-color, discontinuous light, which belongs to kind of Organic Electroluminescent Effect. Varying the chemic componen of the emiconductor material being used, we can make the LED emit a certain light which is very closed to ultraviolet rdiation, visible light and infrared ray.