The Color Rendering Index (CRI) is a scale from 0 to 100 percent, indicating how accurate a given light source is at rendering color, when compared to a reference light source. The higher the CRI, the better the color renderability.
The kelvin is used in the measure of the color temperature of light sources. Color temperature is based upon the principle that a black body radiator emits light whose color depends on the temperature of the radiator. Black bodies with temperatures below about 4000 K appear reddish, whereas those above about 7500 K appear bluish.