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Light is actually made up of colors. For an object to be perceived a certain color, that color must be present both in the object and the light striking it. Because of this, choice of lamp can influence how colors are perceived in a space. This means that perception of objects in the space is, to an extent, controllable. Color Tone: The color temperature of a light source, expressed in kelvins (K), indicates the color tone of the light source itself and the light it emits. Light sources are generally classified as “cool” (>4000K), which appear bluish-white; “neutral” (3000K-4000K), which appear white; or “warm” (<3000K), which appear orangish-white. Warm light sources are more heavily laden with red and orange wavelengths, bringing out some flesh tones and richer content in objects that have warmer colors. Cool light sources are more heavily laden with blue and green wavelengths, enriching the visible color content of blue and green objects.
Color Rendering: Color temperature describes the “whiteness,” “bluishness”, etc. of a light source, its warmth or coolness. However, it does not define how natural the color of objects will appear when lighted by the source. Two light sources can have the same color temperature, but render colors differently. The color rendering index (CRI), a rating scale with a maximum of 100, offers a metric to address this. For most common color temperatures, CRI uses the incandescent lamp as the reference for color rendering (100 CRI). Incandescent lamps, however, are not a perfect light source for color rendering. (They are weak in blue.) So the CRI system has its drawbacks. It is, however, the only internationally agreed upon system for expressing a lamp’s color rendering ability. It should only be used as an indicator of relative, not absolute, color rendering ability.
Performance characteristics of major lamp types. Source: LIGHTFAIR 2009 Lamp and Ballast Basics Seminar by Craig A. Bernecker, PhD, FIES, LC.
Posted on May 27, 2010, 6:40 AM, by Craig DiLouie, under Lighting Design