Hits:Updated:2020-01-17 01:01:31【Print】
LED (Light Emitting Diode), a light-emitting diode, is a solid-state semiconductor device that can convert electrical energy into visible light. It can directly convert electricity into light. The heart of the LED is a semiconductor wafer. One end of the wafer is attached to a bracket, one end is the negative electrode, and the other end is connected to the positive electrode of the power supply, so that the entire chip is encapsulated by epoxy resin.
A semiconductor wafer consists of two parts, one is a P-type semiconductor, where holes dominate, and the other end is an N-type semiconductor, where electrons are mainly. But when these two semiconductors are connected, a P-N junction is formed between them. When a current is applied to the chip through a wire, the electrons are pushed to the P region, where the electrons and holes recombine, and then energy is emitted in the form of photons. This is the principle of LED light emission. The wavelength of light, which is the color of light, is determined by the material that forms the P-N junction.
LED can directly emit red, yellow, blue, green, cyan, orange, purple and white light.
Initially, LEDs were used as indicator light sources for instruments and meters. Later, various light-colored LEDs have been widely used in traffic lights and large-area displays, which have produced good economic and social benefits. Take a 12-inch red traffic light as an example. In the United States, a long-life, low-light 140-watt incandescent lamp was used as the light source, which produced 2000 lumens of white light. After the red filter, 90% of the light is lost, leaving only 200 lumens of red light. In the newly designed lamp, Lumileds uses 18 red LED light sources, including a total of 14 watts of power, including circuit losses, to produce the same light effect. Automotive signal lights are also an important area for LED light source applications.
For general lighting, people need a white light source more. In 1998, the white light LED was successfully developed. This LED is made by packaging a GaN chip and yttrium aluminum garnet (YAG). The GaN chip emits blue light (λp = 465nm, Wd = 30nm). The Ce3 + -containing YAG phosphor produced by high-temperature sintering emits yellow light after being excited by this blue light, with a peak of 550n LED lamp m. The blue LED substrate is installed in a bowl-shaped reflection cavity and covered with a thin layer of resin mixed with YAG, about 200-500 nm. Part of the blue light emitted by the LED substrate is absorbed by the phosphor, and the other part of the blue light is mixed with the yellow light emitted by the phosphor to obtain white light.
For InGaN / YAG white LED, by changing the chemical composition of the YAG phosphor and adjusting the thickness of the phosphor layer, white light of each color with a color temperature of 3500-10000K can be obtained. This method of obtaining white light through a blue LED has the advantages of simple structure, low cost, and high technology maturity, so it is used the most.
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