Some additional notes on the topic:

The author describes color rendering index as a percentage; it is not. It's 100 - [a calculation of average color error on 8 color samples]. Reporting the color error directly would probably be better; 90% and 95% would both be pretty good grades on most tests, but a rendering error of 10 sounds a lot worse than a rendering error of 5.

Being based on only 8 samples, CRI Ra doesn't tell the whole story. There are other standards like TLCI that use more samples, and six supplemental samples some sources report. R9 (strong red) and R12 (strong blue) are particularly relevant to modern lighting, as LED sources often struggle with them despite high CRI (Ra) ratings.

CRI is a comparison to blackbody radiation (like an incandescent bulb) or simulated daylight at the same correlated color temperature as the sample light source. An incandescent bulb and midday sunlight at the equator both have CRI of 100, but a CCT of 2700K and a CCT of 5700K will render colors very differently. White balance in a camera's settings or raw development software can make one look like the other.

CCT is roughly blue-yellow balance, but light sources can deviate from blackbody radiation on a red-green axis. This is most often expressed as "delta u v" or "Duv", as it refers to distance in the CIELUV color space[0]. Duv numbers are small, with differences of less than 0.001 being noticeable in a side by side comparison and more than +/- 0.006 falling outside the ANSI standard for white light. Positive numbers are green, and negative numbers are red/pink.

[0] https://en.wikipedia.org/wiki/CIELUV