Principles of LED Light Products

LED (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 an LED is a semiconductor chip, with one end attached to a bracket, one end being the negative electrode, and the other end connected to the positive electrode of a 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 the current passes through the wire and acts on the 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.

LEDs can emit red, yellow, blue, green, blue, orange, purple, and white light directly.

Initially, LED was used as an indicator light source for instruments and meters. Later, various colored LEDs were widely used in traffic signals and large-area displays, producing 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 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 electricity and produce the same light effect. Car signal lights are also an important field for the application of LED light sources.

For general lighting, people need white light sources more. The development of LED emitting white light was successful in 1998. This type of LED is made by encapsulating GaN chips and yttrium aluminum garnet (YAG) together. GaN chip emits blue light（ λ The YAG fluorescent powder containing Ce3+produced by high-temperature sintering (p=465nm, Wd=30nm) emits yellow light after being excited by this blue light, with a peak of 550n LED light m. The blue light LED substrate is installed in a bowl shaped reflector cavity, covered with a resin thin layer mixed with YAG, about 200-500nm. The blue light emitted by the LED substrate is absorbed by the fluorescent powder, and another part of the blue light 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 construction, low cost, and high technological maturity.