How to improve CRI of LEDs? (3)

Theoretically, white rays can be obtained by combining three primary colors in a certain ratio (red : green : blue = 3:6:1). This technology can be used in LED display but not in LED lighting products, since it is based on the premise that we have seen the object. Objects can be seen by us due to the light reflected from them. During this process, lights will be absorbed by objects. Therefore, white rays generated by the combination of three primary colors have innate defects: objects absorb red rays, blue rays and green rays at different levels. Even they have been mixed exactly in ratio to create purely white rays, after reflecting, they cannot maintain the original ratio, leading to a distortion. That means, lit by LED lamps, objects will look different from looking them in the sun. CRI of LEDs reduces. However, it is not to say that this kind of technique is infeasible. The photo-mixing operation should be taken within LED lamps (before sending out) to improve the CRI of LEDs.

 

Three primary color LED photo-mixing technology is much mature currently. There are two different ways for photo-mixing: on the surface of LED chips; on the surface of lamp covers. Both of them have disadvantages. The former: distances between LED chips are too far for photo-mixing, causing inevitable distortions. The latter: this method will cause light attenuation. Although this type of LED lamps has a higher CRI, lights sent out by them are no longer white rays if captured by our eyes directly.

 

In recent years, many studies for three primary colors LED photo-mixing technology are focus on these two problems. Studies demonstrate that with the decrease of distances between LED lights, light mixing distances exponentially reduced. With the increase of color-scattered agent’s concentration, the light mixing effect will be increased. The balance point between LEDs’ distances (reduce) and color-scattered agent’s concentration (increase) will be the optimal value. With such solution, it is possible for photo-mixing LEDs to be white lighting sources one day.

 

This technology can be used in LED display but not in LED lighting, since it is based on the premise that we have seen the object.

 

Feature above depicts relation between light intensity and concentration of color-scattered agent. From it we can see that light attenuation is proportional to color-scattered agent’s concentration. Currently, transparent glue has a light attenuation of 5%, while glue with color-scattered agent has a light attenuation of 12%. With current technology, this problem will not be solve in short term.