LED (Light Emitting Diode), light emitting diode, is a solid state semiconductor devices of electric energy translated into visible light, it can be directly converted to electric light. Heart of the LED is a semiconductor chip, the chip attached to a bracket on the end, negative electrode at one end and the other end to connect the power of positive, the whole wafer was encapsulated by epoxy resin. Semiconductor chip is composed of two parts, the part of the p-type semiconductor, in the dominant position it inside the hole, and the other end is the n-type semiconductor, here is mainly electronic. But when I connect the two semiconductor, a p-n junction formed between them. When a current passes through the wire act on the chip when electron is pulled into a p-region, electrons with holes in the p-compound then energy as a photon, which is the principle of LED lights glow. And the wavelength of the light is the color of the light, is decided by the formation of p-n junction of the material.
Initially LED as a light source for instrumentation, then various color of LED traffic lights and has been widely used in large-area displays, producing good economic and social benefits. With 12 inches of red traffic lights, for example, in the United States is the use of long-life, low luminous efficacy in 140-watt incandescent lamp as the light source, it produces 2000 lumens of white light. After the red filter light loss 90%, only 200 lumens of lights. In the light of new designs, Lumileds Corporation 18 red LED light sources are used, including circuit losses, total power consumption 14 w, you can produce the same luminous efficiency. Car lights are also important areas of application of LED light source.
For general lighting, people need a white light source. In 1998 LED the successful development of the white light. This LED to GaN chip and yttrium aluminium Garnet (YAG) packaged together to make. GaN chip blue (λ p=465nm,Wd=30nm), high temperature sintering of Ce3+ YAG Phosphor by this Blu-ray activated yellow light, m peak 550nLED lamp. Blue LED mounted on the Bowl-shaped reflecting cavity of the substrate and covered with resin mixed with YAG thin layer, about 200-500nm. Blu-ray part of the issue is the phosphor LED substrate absorption, another part of mixing blue and yellow phosphor issued, you can get white light. InGaN/YAG white LED, by changing the chemical composition and regulation of YAG phosphor phosphor layer thickness, color temperature 3500-10000K colors of white light can be obtained. This method of obtained by blue LED light, simplicity, low cost, high technology is mature, therefore the use of the most.
