The ability of the human eye to see the world in color and to perceive the smallest variations in the color of objects and illuminated spaces enriches the visual experience beyond measure.
A major factor in the perception of color is the light source that is illuminating the object or space. The perceived color of an object is the color of the light reflected or transmitted by the object when it is illuminated.
For example, if you purchase a new red sweater in a shop illuminated by typical fluorescent lights and then walk out of the store into a bright blue sky day, the red sweater will have a slightly different perceived color compared to how it appeared inside the shop. The light source changed, the perceived color changed.
The importance of the light source on perceived color is why the lighting industry has developed a metric to help buyers of light bulbs and light fixtures purchase the appropriate lighting products for specific applications.
Color Rendering Index (CRI)
The term color rendering describes how a particular light source that is illuminating an object makes that object appear compared to how it will appear when illuminated by a different light source.
The Color Rendering Index (CRI) is a scale from 0 to 100 percent indicating how accurate a specified light source is at rendering color when compared to a "reference" light source - usually daylight.
The higher the CRI, the better the color rendering ability. Incandescent and halogen light sources have a CRI close to 100. LED, fluorescent and metal halide light sources with a CRI of 85 to 90 are considered good at color rendering. These same light sources with a CRI of 90 or higher are excellent at color rendering.
For example, if the shop where you purchased the red sweater had LED light fixtures producing illumination with a CRI of 95, the difference in the color appearance of the sweater when you walked out of the store into a bright day would have been minor compared to the shop illuminated with fluorescent bulbs with a CRI of 80.