LED, Light Emitting Diode, is a solid state semiconductor devices, which can directly converte electricity into light. Its heart is a semiconductor chip, which is attached to one end of a stent, the negative pole, and the other end to the positive pole of the power , which makes the entire chip to be epoxy resin packaged. Semiconductor chip is composed of two parts. One is P-type semiconductor, where inside is hole-dominated, and the other one is the N-type semiconductor, where there is mainly electronic. When linking these two semiconductors together, a "PN junction" will form between them. When current goes through the wire and works on this chip, electronic will be pushed towards P zone, where it complex with the hole, and then to be issued in the form of photon energy, and this is the principle of LED luminescence. The wavelength of light, namely the color of light, is decided by the material which forms the PN junction.