Short recap on the key light specifications
In order to create desired lighting effects, lighting designers need to be familiar with the different characteristics that express the color of white light. Correlated Color Temperature (CCT) is used to indicate the color appearance (or tint) of white light. CCT values indicate the apparent warmth or coolness of a light source. Lighting with a CCT value between 2700 K and 3000 K emits more energy at the red end of the spectrum and therefore appears somewhat reddish, which is associated with warmth. On the other hand, lighting with a CCT value of 4000 K and above, emits more energy at the blue end of the spectrum and hence appears more bluish, which is associated with coolness. However, CCT alone does not fully define white appearance since two light sources with the same CCT value can have very different visual appearances. That’s because the exact position of the chromaticity coordinates also contributes to the perception of whiteness.
Color Rendering Index (CRI) is a fidelity index that indicates how close, on average, the colors of objects appear when illuminated by a test source in comparison to a reference illuminant. CRI 100 is the maximum value, meaning that the light in question is as close as possible to the reference light source. Lower CRI values indicate that some colors may appear different in comparison to the reference illuminant.
Another index that is currently being standardized within CIE, and is closely related to CRI, is the Color Gamut Index (CGI). The colors of an object illuminated by a light source with a high CGI (CGI > 100) will appear, on average, more saturated, whereas the colors of an object illuminated with a lower CGI light source (CGI < 100) will appear, on average, less saturated. Whereas CRI only indicates there is a difference in color appearance between the test source and the reference illuminant, CGI indicates the direction of the difference: more or less saturation.