LED, a light-emitting diode, is a solid semiconductor device capable of converting electrical energy into visible light, which can directly convert electricity into light.
The heart of the LED is a semiconductor wafer, one end of which is attached to a bracket, the other end is the cathode, the other end is connected to the cathode of the power supply, so that the entire wafer is encapsulated by epoxy resin. Semiconductor wafers consist of two parts, one of which is a P-type semiconductor, in which the holes dominate, and the other end is n-type semiconductors, which are mainly electrons on this side. But when the two semiconductors are connected, they form a p-n knot between them. When the current passes through the wire on the wafer, the electrons are pushed into the P zone, the electrons are combined with the holes in the P zone, and then the energy is emitted in the form of photons, which is the principle of the LED lamp glowing.
The wavelength of light, also known as the color of light, is determined by the material that forms the p-n knot. LEDs can be directly emitted red, yellow, blue, green, green, orange, purple, white light.  The original LED as an indicator light source for instrumentation, and later a variety of light color LEDs in traffic lights and large area display has been widely used, resulting in good economic and social benefits. In the United States, for example, a 12-inch red traffic signal, a 140-watt incandescent lamp with a long life and low light performance as a light source, produces 2000 lumens of white light. After the red filter, the light loses 90%, leaving only 200 lumens of red light. In the newly designed lamp, Lumileds company uses 18 red LED light sources, including circuit loss, a total of 14 watts of power consumption, can produce the same light efficiency.
Automotive signal lights are also an important field in the application of LED light sources. For general lighting, people need a white light source more. 1998 of White Light led development successfully. This led is made by encapsulating the GAN chip and the yttrium aluminum garnet (YAG) together. Gan Chip Blue Light (λp=465nm,wd=30nm), high temperature sintering made of ce3+ YAG phosphor by this Blu-ray excitation after the issuance of yellow radiation, peak 550nLED lamp m. The Blu-ray led substrate is mounted in a bowl-shaped reflector cavity, covering a thin layer of resin mixed with YAG, about 200-500nm.
The Blu-ray part 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 get white light. For Ingan/yag white LEDs, by changing the chemical composition of YAG phosphor and adjusting the thickness of the phosphor layer, you can obtain color temperature 3500-10000k of all kinds of white light.
This method of getting white light through Blu-ray LEDs is simple in construction, low in cost and high in technical maturity, so it is most used.