Color Rendering Index (CRI or Ra)
CRI measures the ability of a light source to accurately reproduce colors and is measured on a scale from 0 to 100. Natural light has a CRI of 100 and is what all light sources strive to replicate (top picture). A CRI of 65 is considered poor (bottom picture) while a CRI of 80 is considered good. Halogen and Incandescent sources have CRIs close to 100, while fluorescent sources are usually around 80. ENERGY STAR® requires a CRI of 80 for integral LED lamps.
CRI for LED lamps is measured in an integrated sphere which analyzes the chromatic effect of the light source over a scale of 14 standard colors (R1-R14). After testing, each color receives a value. The actual CRI number is derived from taking an average of the values assigned to R1-R8.
Although the R9-R14 values are measured, they have no impact on a product’s CRI rating. R9 includes reds associated with things like food, clothing, and even skin tones. For commercial lighting, it is important to consider an LED’s CRI as well as the R9 value, especially in places like supermarkets, clothing stores, and other places where reds are prominent colors.