led lighting emitting principle
LED (Light Emitting Diode), light-emitting diode, is a solid state semiconductor devices, it can put electricity into light.
The heart of the LED is a semiconductor chip, the chip is fixed on a bracket, is the negative side, the other end connected to the positive power supply, so that the whole chip is epoxy encapsulated. Semiconductor wafer consists of two parts, part of the P-type semiconductor, dominated by the hole in it, the other end of the N-type semiconductor, here is mainly electronic. These two semiconductor connected between them to form a PN junction. When the current through the wire on the chip, the electrons will be pushed to the P region, the P zone electron hole recombination, and then will be issued in the form of photons of energy, which is the principle of LED light. And the wavelength of light that is the color of the light is determined by the material forming a PN junction.
The initial LED as a light source instrumentation instructions, then each light color LED traffic lights and a large area of the display has been widely used, resulting in a very good economic and social benefits. 12-inch red traffic lights, for example, in the United States was using long-life, low-efficiency 140-watt incandescent lamp as a light source, which produces 2,000 lumens of white light. The red filter, 90% light loss, only the red light of 200 lumens. In the light of the new design, Lumileds uses 18 red LED light source, including circuit losses, a total power of 14 watts to produce the same light efficiency. Car lights are also important areas of application of LED light source.
For general lighting purposes, people need a white light source. 1998 white LED development. This LED is GaN chip and yttrium aluminum garnet (YAG) packaged together to make. GaN chip emits blue light (λp = 465nm, Wd = 30nm), yellow and irradiating Ce3 +-containing high-temperature sintering the YAG phosphor affected by blue light excitation peak of 550 nm. Blue LED substrate mounted on the the reflective cavity bowl, cover mixed with YAG thin layer of resin, about 200-500nm. The blue light emitted by the LED substrate is absorbed by the phosphor can be too white, and some blue phosphor issued yellow mixed. For InGaN / YAG white LED, by changing the chemical composition of the YAG phosphor and adjusting the thickness of the phosphor layer can be colored white color temperature 3500-10000K. This phosphor excited by blue LED white light, simple structure, low cost, high technology is mature, and therefore use the most.
