The higher the luminous efficacy of the LED is, the lower the color rendering index (CRI) is? And the importance of R9 spectrum
The higher the luminous efficacy of the LED is, the lower the color rendering index is? No, this theory is clearly unsustainable. The causality of this logic is reversed. Not the luminous efficacy is low, so the CRI is high. But to improve CRI, so we have to sacrifice some luminous efficacy. However, many people still have misunderstandings about the luminous efficacy, they thought Luminous efficacy is Luminous effect.
Luminous Efficacy: The luminous flux (lm) emitted by an LED light source divided by the
power consumed by the light source (W) is called the luminous
efficiency of the LED, The unit is lm/W.
Luminous effect refers to the visual effect. So it is different from Luminous Efficacy.
They are two different concepts.
Factors Influencing Color Rending Index (CRI)：
Most commercial LED chips are coated with yellow phosphor (YAG), which can be stimulated by the blue light, we usually call it yellow powder. The blue light emitted by the chip complements and the yellow light emitted by the phosphor powder, synthesize the white light.
If you want to improve the color rendering of LED, you need to involve the calculation of color rendering index. Generally, the calculation of color rendering index is R1-R8, and the chromatogram is relatively narrow.
But there is still a lack of a very important spectrum, which is the special reference R9, red R9 (saturated red color),it is an index to evaluate the quality of red reproduction. For their application studios and other occasions that need to truly reproduce skin color, as well as for the color reduction of fresh meat and vegetables has an irreplaceable role.
R9 is also an important indicator to measure the color rendering of LED. You will notice it from the following pictures, the greater the R9 is, the better the red color of vegetables and fruits is.
How Greeled improve the color rendering index of LED?
There is a saying "what is missing, to make up for what", which can not be used here more accurately. As it is missing R9, so "make up R9", then how to make up for it?
Adding red phosphor can make up for the deficiency of red spectrum of LED and adjust the color index of white LED. For example, if the original color index of an LED is 70, it may only need a little red phosphor to increase the color index of 80. To achieve the color index of 90, It is necessary to increase the concentration of red powder by multiple.
