Light Bulbs Alter True Colors
Kelvin and Color Rendition Scales
Kelvin Scale Comparative Values
The following list gives you a feel of where certain light sources are relative to one another on the Kelvin scale.
- High Pressure Sodium
- Regular Incandescent Bulb
- Warm Fluorescent Bulb
- Some Halogen Bulbs
- Mid Range Fluorescent Bulbs
- Cool Fluorescent Bulb
- Some Metal (Mercury)Halide Bulbs
- Special Fluorescent Bulbs
- North Blue Sky light in low pollution area, low humidity, ideal weather conditions, high noon
Color Rendering Index
The color rendering index is an arbitrary scale of 0 to 100. It was developed in the 1930's, before fluorescent lights. True color samples (8) picked by the international lighting community are used to test the manner in which a particular bulb affects the color of the samples. Since the color of the sample is known, the amount that its color changes because of the bulb illumination determines the bulb's scale rating.A 0 rating would be the absolute worst, with a score of 100 being perfect.
Ratings can be all over the scale. For example, certain mercury vapor lamps have a CRI rating of 20! That is why your car looks weird in some parking lots at night. Some fluorescent bulbs have a CRI rating as high as 90.
For comparative shopping, any bulb with a CRI rating of 70 or higher will produce excellent color rendition. Values between 60 and 70 would be considered good. Below 60, and you run the risk of poor color rendition. Be careful!