To avoid metamerism (colors that match under one color source but not under another), samples to be matched should be compared under two widely different sources, i.e., daylight fluorescent (lacks red) and incandescent (lacks blue). If the samples match under both of these sources alternately, they will likely match under any source. A simple, white painted box with two F20T12/D fluorescent lamps and two 40-watt silver bowled lamps, separately switched, is all that is needed to solve most color matching problems.

Color Selection

The choice of lamp color and space color(s) is the prerogative of the lighting consultant, the interior designer, and the owner. The decisions should be made jointly since the interaction of the light and colored objects will affect the success of the installation.

There are a number of common sense rules of thumb that can help make color selection easier:

• All space colors (wall and floor covering, furniture, drapes, accents, etc.) should be chosen under the lamp color specified for the installation. Experience suggests that warm sources should be used at low lighting levels, cool sources at high levels. However, the choice may be influenced by space colors and by degree of luminaire brightness control.
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• Warm color schemes may appear overpoweringly warm is lighted with a warm source to relatively high levels - use a cooler source.
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• Cool color schemes may need warm sources, particularly at low lighting levels.
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• Where color rendition is critical, use high CRI continuous spectrum sources such as fluorescent lamps with Chroma 50 (C50) or Chroma 75 (C75) phosphors.
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• Where both color and lighting level are important, use the SP30, SP35, or SP41 tri-Phosphor fluorescent lamps for good color rendering and high efficiency. For even better color rendering and higher efficacy, consider GE's SPX30, SPX35 or SPX41 lamps.
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• Tri-Phosphor lamps tend to make spaces look more colorful because the 3-peak phosphors compress all colors into the blue, green, and red-orange bands. This increases the contrast between colors. Three peak lamps do not, however, increase the contrast of black and white tasks. Claims that less light is needed for typical office and industrial tasks when they are used are scientifically unfounded.
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• The color of a light source does not affect the visual performance of people doing black-on-white visual tasks. Vision and productivity studies, however, indicate that productivity may be affected by the color contrast and appearance of the visual environment and that color can contribute strongly to appearance.