Quick Answer: CRI (Color Rendering Index) measures how accurately a light source renders color compared to sunlight, with 90+ considered high quality. CRI itself is a single number, and this is both a blessing and a curse. It is a great, convenient metric that is both intuitive and simple to communicate, but at the. What is the difference between Kelvin and CRI? The CRI or R9 is very different than Kelvin. They are not used for calculation of CRI but may be used for supplemental analysis when necessary. The “strong red” color sample, R9, is especially 5 The reference is specified as blackbody. For example, R9 is a deep red—a critical reference color for many applications such as lighting in butcher shops, grocery stores, and medical settings.