For general lighting, people need a white light source. In 1998, the white LED was successfully developed. This LED is made by encapsulating a GaN chip and yttrium aluminum garnet (YAG). The GaN chip emits blue light (λp=465nm, Wd=30nm), and the Ce3+-containing YAG phosphor produced by high-temperature sintering 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 reflective cavity, covered with a thin layer of resin mixed with YAG, about 200-500nm. The blue light emitted by the LED substrate is partially 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.