The Color Rendering Index (CRI) is a quality metric that measures a light source's ability to accurately reproduce colors compared to a reference source (like natural daylight). CRI is expressed as a number between 0 and 100; a high CRI (90+) indicates better spectral quality and truer color reproduction.

CRI is related to, but distinct from, Standard Illuminant D50. D50 (5000 Kelvin) represents the required Color Temperature for the printing industry (neutral), while CRI represents the spectral quality of that 5000K light. To guarantee Color Accuracy, a print house must use a light source that is both 5000 Kelvin and has a high CRI. A low CRI, even at the D50 temperature, causes spectral gaps that can render printed colors dull or with unwanted tints (like blue) and makes detecting subtle color deviations impossible.