Color Rendering Index (CRI) is a way to measure a light source's distinctive attributes. It is an assessment of how the light source shows object colors "naturally" when compared to a familiar basis of reference, either incandescent light or daylight.
What is a Good CRI?
The color rendering index (CRI) is measured as a number between 0 and 100. At zero (0), all colors look the same. A CRI of 100 shows the true colors of the object. Incandescent and halogen light sources have a CRI of 100.
Typically, light sources with a CRI of 80 to 90 are regarded as good and those with a CRI of 90+ are excellent! The general rule is: The higher the CRI, the better the color rendering capacity.
CRI is independent of color temperature. These are two different things. For example, a 5000K (daylight color temperature) fluorescent light source could have a CRI of 75, but another 5000K fluorescent light source can have a CRI of 90.
This chart is a good depiction of differing CRIs, with each image having the same warm color temperature (2700K):