CRI, or Color Rendering Index, is a measurement of a light source's accuracy in rendering different colors when compared to a reference light source with the same correlated color temperature. It generally ranges from 0 for a source like a low-pressure sodium vapor lamp, which is monochromatic, to 100, for a source like an incandescent light bulb, which emits essentially blackbody radiation. The higher the CRI, the better the visual perception of colors. CRI is related to color temperature, in that the CRI measures for a pair of light sources can only be compared if they have the same color temperature (see Color Temperature Chart).
The highest attainable CRI is 100. Lamps with CRIs above 70 are typically used in office and living environments. A standard "cool white" fluorescent lamp will have a CRI near 62.