Messages

Subject:
Explanation of CRI
Response To:
What is "CRI" Please *NM* ()

Bill Tindall, E.Tn.
Color Rendition Index

I don't know the details of how it is measured but the result is easy to explain. We have sun light and we have man made light from some lamp or another. If an object looks the same in this artificial light as in sun light the CRI is 100.

If the CRI of some artificial light is 93 likely only an expert in color matching could tell a difference from looking at it in the sun.

An artificial light has a CRI less than 100 because there is some color component of the artificial light that is missing or out of balance. In the case of the experiment I reported on the Max Light LED, this lamp was likely deficient in red and green which made the light harsh. (LED lights are inherently blue and need to be made redder and greener by some means. A cheaply made LED might skimp on adding these colors. )

You have probably seen the yellow "sodium" lamps used for street lighting. Stuff looks strange under their illumination. I don't know their CRI but it might be 20, or some other small number.

CRI is critical to color matching. You can be sure that the lamps lighting the paint strips in Lowes are very high CRI and the same for a designer clothing store. But crappy CRI can also have a psychological component, as demonstrated by the adverse reaction the bystander had to the Max Light or I have to crappy fluorescent lamps with a CRI of 60 or 70.

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