The principle of LED lights

LED (Light Emitting Diode) is a solid-state semiconductor device that can convert electrical energy into visible light, which can directly convert electricity into light. The heart of an LED is a semiconductor chip, one end of which 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, making the entire chip encapsulated in epoxy resin.
A semiconductor chip consists of two parts, one is a P-type semiconductor in which holes dominate, and the other is an N-type semiconductor in which electrons dominate. But when these two semiconductors are connected, a P-N junction is formed between them. When an electric current passes through a wire and acts on this chip, electrons are pushed towards the P region, where they recombine with holes and emit energy in the form of photons. This is the principle of LED light emission. The wavelength of light, also known as the color of light, is determined by the material that forms the P-N junction.
LED can directly emit red, yellow, blue, green, blue, orange, purple, and white light.
Initially, LED was used as an indicator light source for instruments and meters. Later, various color LEDs were widely used in traffic lights and large area displays, resulting in good economic and social benefits. Taking the 12 inch red traffic light as an example, in the United States, a 140 watt incandescent lamp with a long lifespan and low visual efficiency was originally used as the light source, producing 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 uses 18 red LED light sources, including circuit losses, which consume a total of 14 watts of power, producing the same light effect. Car signal lights are also an important field for the application of LED light sources.
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 fluorescent powder containing Ce3+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 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.
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. This method of obtaining white light through blue LED is widely used due to its simple structure, low cost, and high technological maturity.