Things to note when making white light LEDs that synthesize RGB three primary colors

When making white light LEDs that synthesize RGB three primary colors, the following issues must be noted:

(1) The dominant wavelengths of light emitted by the three LED chips are generally: 615~620nm for red light, 530~540nm for green light, and 460~470nm for blue light. To achieve the best lighting effect, the best dominant wavelength ratio can be selected through experiments within the dominant wavelength range of these three lights. If you want to improve the color rendering index, you can use a combination of blue light (460nm), green light (525nm), yellow light (580nm), and red light (635nm). This dominant wavelength ratio of light can obtain the best color rendering index (above 95), the lighting effect can reach 35~40lm/W, and the lowest color temperature can reach 2700K. In order to take into account both the light output efficiency and the color rendering index, the dominant wavelength and luminous intensity of the light emitted by the three LED chips need to be optimized. Performing several experiments according to the model and materials used can obtain the best effect.

(2) The ratio of the luminous intensity of the three LED chips, red, green and blue, is generally 3 (red): 6 (green): 1 (blue), but it is necessary to consider that the light decay of different chips is different; and when they are lit and heated, the main wavelength drift of the three primary colors of light is also different. Considering these factors at the same time, a comprehensive experiment is conducted to obtain the best effect, so the above ratio is only a reference, not a fixed conclusion.

(3) If the three LED chips are simply arranged and packaged together, the three LED colors cannot be mixed well into white light. Figure 1 shows a schematic diagram of RGB color mixing. Only area A has all three colors, so only area A is white light, and other areas are not white light. The light energy emitted by the three RGB chips is mainly distributed within a certain angle centered on the optical axis of the light source. Therefore, the light emitted by different chips at different positions can only overlap and mix colors after propagating a certain distance. However, even after propagating a certain distance, white light still only appears in the central area, that is, the areas outside the central area are still not mixed, and the light with a larger divergence angle moves away from the center after propagation, which in turn causes a decrease in luminous efficiency.

Figure 1 Mixture of RGB primary colors

Therefore, how to efficiently mix light within a short propagation distance is the key to packaging high-quality three-primary-color white light LEDs. This problem can only be solved through special packaging design, as shown in Figure 2. After adopting this structure, the three types of light are basically concentrated in one area for mixing, so when making three-primary-color synthetic white light LEDs, some special structural designs should be implemented on the heat sink and the die, so that the three primary colors of light can be mixed in a concentrated area to produce effective white light.

Figure 2 Special structural design for mixing three primary colors

(4) When multiple chips are packaged in one device, it is more difficult to dissipate heat. Therefore, when mixing RGB primary colors into white light, special attention should be paid to heat dissipation. The temperature characteristics of these three chips are different, and temperature changes will cause color temperature deviation. Table 1 compares the production effects of several major white light LEDs.

Table 1 Several main white light LED production effects