Does the higher the luminous efficacy of the LED, the lower the color rendering index (CRI)? and R9 spectrum importance

The higher the luminous efficacy of the LED, the lower the color rendering index,This Theory is clearly unsustainable. First of all, 

The causality of this logic is reversed, Not beacuse the luminous efficacy is low, So CRI is high.But in order to improve CRI and

 sacrifice some luminous efficacy.However, many people still have some misunderstandings about the luminous efficacy.

they think 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 units is  lm/W. 

Luminous effect refers to the visual effect. so it is different from Luminous Efficacy. They are two concepts.

Factors Influencing Color Rending Index：

Most commercial LED chips are coated with yellow phosphor (YAG) which can be stimulated by blue light. We usually call it yellow
powder. The blue light emitted by the chip complements the yellow light emitted by the phosphor powder to form white light.

If you want to improve the color rendering of LED, it needs 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.

The greater the R9, the better the red color of vegetables and fruits under different R9.

How can Greeled improve the color rendering index of LED?

There is a saying called "what is missing to make up for what", which can not be used here more accurately. Since it is missing R9,
then "make up R9",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.