As everyone knows, the wavelength range of the visible light spectrum is 380nm to 760nm, which is the seven colors of light that the human eye can perceive - red, orange, yellow, green, cyan, blue, and purple, but these seven colors of light are each. A monochromatic light.
For example, the peak wavelength of red light emitted by an LED is 565 nm. There is no white light in the spectrum of visible light, because white light is not monochromatic light, but a composite light composed of multiple monochromatic lights, just as sunlight is composed of seven monochromatic lights. White light is also synthesized from the three primary colors red, green and blue.
It can be seen that to make an LED emit white light, its spectral characteristics should include the entire visible spectral range. But to make LEDs of this performance is impossible under process conditions. According to people's research on visible light, the white light that the human eye can see requires at least a mixture of two kinds of light, that is, two-wavelength light (blue light + yellow light) or three-wavelength light (blue light + green light + red light) mode . Both the above-mentioned white light modes require blue light, so the absorption of blue light has become a key technology for manufacturing white light, that is, the "blue light technology" currently pursued by major LED manufacturing companies. There are only a few manufacturers who have mastered "blue light technology" in the world, so the promotion and application of white LEDs, especially the promotion of high-brightness white LEDs in my country, still has a process.
For general lighting, in terms of process structure, white LEDs are usually formed by two methods. The first is to use "blue light technology" to cooperate with phosphors to form white light; the second is to mix a variety of monochromatic light. Both methods have been successful in producing white light devices. In the first method to generate white light, the LED GaM chip emits blue light (λp=465nm), which is encapsulated with YAG (yttrium aluminum garnet) phosphor powder. When the phosphor powder is excited by blue light, it emits yellow light. As a result, blue light and Yellow light mixes to form white light. The second method uses chips of different colors to be packaged together to generate white light by mixing the colors.