At present, there are three main methods to realize white light in LED:
1, through the LED three primary colors red green blue, multi chip group and the synthesis of white light luminescence.
Advantages: high efficiency, controllable color temperature and better color display.
Disadvantages: three color light color temperature leads to different instability, complex control circuit and high cost.
2, Blu ray LED chip stimulates yellow phosphor. The yellow green light emitted from LED blue and phosphor is used to synthesize white light. In order to improve the color rendering performance, we can add a small amount of red phosphor or add proper amount of green and red phosphor to it.
Advantages: high efficiency, simple preparation, better temperature stability and better color display.
Shortcomings: poor consistency, color temperature changes with the angle.
3, ultraviolet LED chip stimulates the phosphor to produce three basic colors to synthesize white light.
Advantages: good color rendering and simple preparation.
Shortcomings: at present, the efficiency of LED chip is low, there are ultraviolet light leakage, and the temperature stability of the phosphor needs to be solved.
Characteristics of UV LED + RGB three color fluorescence scheme
Advantage：
1) the white coordinates are determined only by the phosphor itself, independent of the excited chip (it can tolerate the dispersion of the LED chip).
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.
Shortcomings:
1) the leakage of ultraviolet light will destroy the LED sealing, which leads to the problem of device life.
2) light conversion efficiency is not high, self absorption, light transmittance and so on.
The challenges faced:
1) no experiments have been done so far.
2) there is no phosphor that can stimulate blue light at present.
3) the color changes with the change of the angle of observation.
4) sealing must be able to resist the destruction of ultraviolet light.
5) the stability of RGB phosphor remains to be further enhanced.
Characteristics of LED (Blue) + phosphor (Yellow) scheme
Advantage：
1) only a single phosphor is made relatively simple.
2) the fluorescent powder with single blue light has been mature, and the source of the goods is abundant.
3) the color of the white light is moderate (RI? 75%).
4) the stability of the phosphor can already meet the requirement of the degree of color reduction.
Shortcomings:
1) light conversion efficiency is not high, self absorption, light transmittance and so on.
2) the degree of color reduction is not high enough.
3) the stability of the color is greatly influenced by the temperature and the driving current.
4) the color changes with the observation angle.
Characteristics of RGB three color LED color mixing scheme
Advantage：
1) the photoelectric efficiency is the highest. From the point of view of the long-term development, this scheme will be the mainstream.
2) the optional color adjustment can be realized.
3) excellent color rendering ability (RI).
4) very wide range of color gamut.
Shortcomings:
1) complex color characteristics compensation feedback control, the characteristics of the LED material varies with temperature, and the attenuation characteristics of LED.
2) the adjustment of color is very strange and changeable.