CRI (Color Rendering Index, also denoted Ra) is a quantitative measure (0–100) of how accurately a light source renders colors compared to a reference illuminant (daylight or incandescent). CRI≥90 is considered excellent (museums, retail, healthcare). CRI≥80 is standard for commercial offices. CRI<70 is acceptable for industrial/outdoor applications. Extended CRI includes R9 (saturated red)—critical for skin tones, food, and art. Note: CRI alone doesn't capture color preference; TM-30-18 provides a more comprehensive 99-color-sample analysis.