LED (light emitting diode)
, is a solid-state semiconductor device that can convert electric energy into visible light. It can directly convert electricity into light. The heart of LED is a semiconductor chip. One end of the chip is attached to a bracket, one end is the negative pole, and the other end is connected to the positive pole of the power supply, so that the whole chip is encapsulated by epoxy resin.
The semiconductor chip of the LED light
consists of two parts. One part is a p-type semiconductor, in which holes dominate, and the other end is an n-type semiconductor, mainly electrons. But when the two semiconductors are connected, a p-n junction is formed between them. When the current acts on the chip through the wire, the electrons will be pushed to the p region, where the electrons and holes compound, and then emit energy in the form of photons. This is the principle of LED light emission. The wavelength of light, that is, the color of light, is determined by the material forming the p-n junction.
can directly emit red, yellow, blue, green, green, orange, purple and white light.
At first, LED light
was used as the indicator light source of instruments and meters. Later, LED of various light colors was widely used in traffic lights and large-area display screens, resulting in good economic and social benefits. Take the 12 inch red traffic signal lamp as an example. In the United States, 140 watt incandescent lamp with long service life and low luminous efficiency was originally used as the light source, which produced 2000 lumens of white light. After passing through the red filter, the light loss is 90%, leaving only 200 lumens of red light. In the newly designed lamp, Lumileds adopts 18 red LED light sources, including circuit loss, which consumes a total of 14 watts to produce the same light effect. Automobile signal lamp is also an important field of LED light source application.
For general lighting, people need white light source more. In 1998, white LED was successfully developed. This led is made of Gan chip and yttrium aluminum garnet (YAG). Gan chip emitting blue light（ λ P = 465nm, WD = 30nm), YAG phosphor containing Ce3 + made by high-temperature sintering emits yellow light after being excited by this blue light, with a peak value of 550n LED lamp m. The blue LED substrate is installed in the bowl shaped reflecting 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 LEDs, various colors of white light with color temperature of 3500-10000k can be obtained by changing the chemical composition of YAG phosphor and adjusting the thickness of phosphor layer. This method of obtaining white light through blue LED has the advantages of simple structure, low cost and high technical maturity, so it is used most.