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Background Information:
Fluorescent lamps emit wavelengths in varing degrees from the entire range of the visible spectrum. Most fluorescents will be deficient in at least one of the regions of the color spectrum. This deficiency is why objects appear to be one color outdoos and another color indoors under fluorescent lighting. This is also why objects look one color in the store under fluorescent lighting, and look entirely different when you get them home. (see Full Spectrum Lamps.)
Definition:
CRI (Color Rendering Index) is defined as the effect that a light source has on the appearance of an objects color. In short, CRI is how the lamp makes an object appear.
Measurement:
CRI is a universal measurement system numbering from 0 - 100, with outdoor light having a CRI of 100. Generally, the higher the CRI the better the color rendering properties of the lamp. However, a correct judgement can not be made based upon CRI alone. A second measurement also needs to be considered, Kelvin Temperature.
Background Information:
History of Kelvin Temperature (K) originally comes from the incandescent lamp. In order to understand Kelvin (K) one needs to look at the following example:
When you heat an iron bar the color of the bar changes from dull red, to red-orange, to white as the temperature of the iron bar increases.
In an incandescent lamp the tungsten filament goes through similar color changes as the voltage increases. Thus K measures the change in color appearance.Definition:
Kelvin Temperature (K) is defined as the appearance of a light source. Simply put, how the light source itself appears.
Measurement:
Kelvin is measured in degrees.
Less than 3000 K are considered warm colors and have a reddish appearance. ie: Warm White, Warm White Deluxe, Design Spec 30.
3400 K to 4500 K are considered to be white or neutral in appearance. ie: Natural, Design Spec 35 and 41, and Cool White.
Greater than 4600 K are cool or bluish in appearance. ie: Artic Lite, Sign Lite, Chroma 50, Chroma 75, True Lite, and Daylight.