p4.81 outdoor rental led display.White LED

　　For general lighting, people prefer white light sources. In 1998, LED emitting white light was successfully developed. This type of LED is made by encapsulating GaN chips and yttrium aluminum garnet (YAG) together. GaN chip emits blue light( λ P=465nm, Wd=30nm), high-temperature sintered YAG phosphor containing Ce3+emits yellow light after being excited by this blue light, with a peak value of 550nm. The blue LED substrate is installed in a bowl shaped reflection cavity, covered with a thin layer of resin mixed with YAG, approximately 200-500nm. The blue light emitted by the LED substrate is partially absorbed by the fluorescent powder, while the other part is mixed with the yellow light emitted by the fluorescent powder to obtain white light. Now, for InGaN/YAG white LEDs, by changing the chemical composition of YAG phosphor and adjusting the thickness of the phosphor layer, various colors of white light with a color temperature of 3500-10000K can be obtained.

　　Table 1 lists the current types of white LEDs and their emission principles. The first product that has been commercialized at present is a blue light single crystal chip with YAG yellow fluorescent powder, which has the best luminous efficiency of about 25 lumens/watt. YAG is mostly imported from Nippon Nippon Corporation, with a price of 2000 yuan/kg; The second type is a white LED made of ZnSe, which was also developed by Sumitomo Electric in Japan, but its luminous efficiency is poor.

　　From the table, it can also be seen that certain types of white LED light sources cannot do without four types of phosphors: rare earth red, green, blue powder with three primary colors, and yellow powder with garnet structure. In the future, three wavelength light is more promising, which is to use inorganic ultraviolet light chips and R.G.B three color phosphors to encapsulate LED white light. It is expected that three wavelength white light LEDs will have the opportunity for commercialization this year. However, the particle size requirements for the three primary fluorescent powders here are relatively small, and the stability requirements are also high. The specific application aspects are still being explored.

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