Visual color matching light source

The conditions necessary for the use of color chips are relevant to all visual color-matching and assessment procedures. Such tasks must be done by individuals with normal color vision, using standard viewing and lighting conditions. The illumination should be white and diffuse, and there should be no interference from extraneous light sources, or reflections from the ceiling or other objects in the room. 

The principal use of the light booth is to compare a colored specimen with a control sample to obtain a visual assessment of the color match. The match and the standard can be compared under a variety of light sources to determine if metamerism is present. Metamerism occurs when a pair of samples appears to match under one light source but not under another. Metamerism is a common phenomenon and often occiurs when the two samples are colored with blends of different colorants. 

For a surface that does not fluoresce, its spectral reflectance characteristics can modify the quantity and geometry of incident monochromatic light, but not its wavelength. Viewed under separate monochromatic light sources of the same wavelength, any two surfaces with arbitrarily chosen spectral distributions can be made to match, both physically and visually, by adjusting the relative radiances of incident lights. Therefore, no chromatic color differences can exist under monochromatic illumination. 

The methods described above are based on additive color mixing, but color can also be specified using subtractive colorimetry. Where the sample is transparent, colored glasses are used to subtract light from a standard source until the resulting color visually matches that transmitted by the sample. 

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