We have stated, and will continue to state, that color depends on the light source, object, and the observer, shown in Figure 7.1. Chapter 1 is focused on the object while Chapter 2 considers the observer. We focus on the light source in this chapter. Many color tolerances are defined using standard illuminants such as D65. We describe how CIE daylight was derived as well as other standard illuminants. All viewing booths have lights that simulate CIE daylight. How well is daylight simulated? The luminous efficiency function, Vλ, is used to calculate luminance, illuminance, luminous efficacy of a source, and luminous efficacy of radiation (LER). These metrics are used to specify the amount of light necessary for a given task and to quantify energy efficiency. The color of a light source is defined by its chromaticity coordinates. However, it is difficult to infer hue from chromaticities. Instead correlated color temperature (CCT) is used. A wide variety of electric lighting is in use today including incandescent, fluorescent, metal halide, and solid state. These lights can have the same CCT, but because their spectral properties are vastly different, colored objects appear differently. The objects have been rendered differently and color rendering indices are used to quantify these differences compared with lights that are assumed to render an object's true color.
Figure 7.1 “Color” results from the interaction of a light source, an object, and the eye and brain, ...
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