What is color rendering index (CRI)?

Click on a picture below to view bulbs within a specific CRI.
Low High
Low High
CRI is a unit of measure that defines how well colors are rendered by different illumination conditions in comparison to a standard (i.e. a thermal radiator or daylight). CRI is calculated on a scale from 1-100 where a CRI of 100 would represent that all color samples illuminated by a light source in question, would appear to have the same color as those same samples illuminated by a reference source. To put it another way, low CRI causes colors to appear washed out and perhaps even take on a different hue, and high CRI makes all colors look natural and vibrant.

This four-foot T12 fluorescent tube (F40DSGN50) has a CRI of 90, which is excellent. While this four-foot T12 fluorescent tube (F40CW/SS/ECO) has a CRI of just 62.