White LEDs are the only way to achieve semiconductor lighting. A white LED is not a monochromatic light, and there is no white light in the spectrum of visible light. According to people's research on visible light, white light that can be seen by human eyes can be produced by mixing two or more kinds of light. There are currently three methods for obtaining white LED illumination sources.
The white LED developed is a yellow phosphor coated by blue LEDs. The yellow light generated by the phosphor is excited and the blue light originally excited. Complementary and produce white light. It is also possible to obtain white light by combining the green light and the red light emitted by the blue LED chip with the phosphor, and the color rendering property is good, but the phosphor conversion efficiency used in this method is low, especially the red phosphor.
At present, the white LED packaging technology using blue LED with yellow phosphor is relatively mature, but the problem of uniformity, high color temperature and poor color rendering index cannot be solved.
The principle of synthesizing white light with ultraviolet or violet (300-400nm) LED and RGB phosphor is similar to that of fluorescent lamp, but superior to fluorescent lamp performance, purple LED conversion The coefficient can reach 0.8, and the quantum conversion efficiency of each color phosphor can reach 0.9.
The method of using violet LED to excite three primary or multicolor phosphors to produce multicolor light and then mixing into white light has better color rendering, but there are also problems. Red phosphor and green phosphor are mostly sulfides, and the light emission stability is poor. The light decay is large.
This method combines three kinds of LED chips of green, red and blue, and simultaneously energizes, and then mixes the emitted green light, red light and blue light into white light according to a certain ratio. The ratio of green, red, and blue is usually 6:3:1. The method of directly packaging R-G.B three primary color LEDs into white LEDs has the best comprehensive performance of white light, and the white light lumen efficiency is also high under the premise of high color rendering index.
Due to the different color temperature and color rendering index required for the synthesis of white light, the lumen efficiency requirements for the LEDs of the composite white light are also different. However, the main technical problem of this method is to improve the electro-optical conversion efficiency of green LEDs and reduce costs.