At present, there are three main methods for LED to achieve white light:

　　1. Synthesize white light through LED red, green and blue three-color multi-chip set and light emission.

　　Advantages: high efficiency, controllable color temperature, good color rendering.

　　Disadvantages: the different light attenuation of the three primary colors leads to unstable color temperature, more complicated control circuits, and higher cost.

　　2. The blue LED chip excites the yellow phosphor, and the blue light and the yellow-green light emitted by the phosphor are synthesized into white light. In order to improve the color rendering performance, a small amount of red phosphor or an appropriate amount of green and red phosphor can be added at the same time.

　　Advantages: high efficiency, simple preparation, good temperature stability, good color rendering.

　　Disadvantages: poor consistency, color temperature changes with angle.

　　3. The ultraviolet LED chip excites the phosphor to emit three primary colors to synthesize white light.

　　Advantages: good color rendering and simple preparation.

　　Disadvantages: At present, the efficiency of LED chips is low, there are problems of ultraviolet light leakage, and the problem of phosphor temperature stability needs to be solved.

　　Features of UV LED + RGB three-color phosphor solution

　　advantage:

　　1) The white coordinate point is only determined by the phosphor itself and has nothing to do with the excitation chip (the discreteness of the LED chip can be tolerated).

　　2) A high color reduction index RI can be achieved.

　　3) In theory, it is the simplest manufacturing scheme.

　　4) The stability of the color light only depends on the phosphor, which can be very stable.

　　Disadvantages:

　　1) Leaking ultraviolet light will damage the LED encapsulant and cause device life problems.

　　2) The light conversion efficiency is not high, self-absorption, light transmittance, etc.

　　Challenges:

　　1) The test has not been successful so far.

　　2) There is no phosphor that can excite blue light.

　　3) The color will change with the angle of observation.

　　4) The sealant must be able to resist UV damage.

　　5) The stability of RGB phosphors needs to be further improved.

　　Features of the LED (Blue) + phosphor (Yellow) solution

　　advantage:

　　1) There is only a single phosphor, which is relatively simple to manufacture.

　　2) Phosphors with blue light alone are mature and abundant.

　　3) The color reproduction of the white light is moderate (RI 75%).

　　4) The stability of the phosphor can already meet the requirements of color reduction.

　　Disadvantages:

　　1) Low light conversion efficiency, self-absorption, light transmittance, etc.

　　2) The color reduction degree is not high enough.

　　3) The color stability is greatly affected by temperature and drive current.

　　4) The color will change with the viewing angle.

　　Features of RGB three primary colors LED color mixing scheme

　　advantage:

　　1) The highest photoelectric efficiency. From a long-term development point of view, this solution will be the mainstream solution.

　　2) Can realize arbitrary color adjustment.

　　3) Excellent color rendering ability (RI).

　　4) Very wide color gamut range.

　　Disadvantages:

　　1) A complex color and light feedback control is required to compensate for the characteristics of LED materials that change with temperature, and the light attenuation characteristics of LEDs.

　　2) The color adjustment is very strange and changeable.