system
Given the following post, respond as if you're commenting on Reddit:
human
I was looking at an LED lighting catalog, and I noticed that a higher color rendering index seems to correspond to a lower efficiency. Is this coincidental, or is there some physical mechanism that causes a negative correlation?
gpt
It's a correlation...

Most white LEDs use blue LEDs with a phosphor that absorbs the blue light and then emits a different colored light. 

To get high CRI indexes, you generally need to add in a phosphor that emits in the red range, but these phosphors are less efficient, so the overall efficiency of the bulb suffers. 

This is an oversimplification; there are tons of different phosphors out there are different ways to get high CRI bulbs.