The working principle of LED lamp

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 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 entire chip is encapsulated by epoxy resin. The semiconductor chip consists of two parts, one part is a P-type semiconductor, in which holes dominate, and the other end is an N-type semiconductor, which is mainly electrons. But when these 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 area, where the electrons and holes recombine, and then they will 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 that forms the P-N junction.

Initially, LED was used as an indicator light source for instruments and meters. Later, LEDs of various light colors were widely used in traffic lights and large-area display screens, producing good economic and social benefits. Take the 12-inch red traffic light as an example. In the United States, a long-life, low-light-efficiency 140-watt incandescent lamp was originally used as the light source, which produces 2,000 lumens of white light. After passing through 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 circuit losses, and consumes a total of 14 watts of power to produce the same light effect. Car signal lights are also an important field of LED light source application.

For general lighting, people need white light sources more. In 1998, white light LEDs were successfully developed. This LED is made by encapsulating GaN chips and yttrium aluminum garnet (YAG) together. The GaN chip emits blue light (λp=465nm, Wd=30nm), and the YAG phosphor containing Ce3+ made by high-temperature sintering is excited by this blue light and emits yellow light with a peak value of 550nm. The blue LED substrate is installed in a bowl-shaped reflective cavity and covered with a thin layer of resin mixed with YAG, about 200-500nm. 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, by changing the chemical composition of the 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 LEDs is simple in structure, low in cost, and highly mature in technology, so it is the most widely used.