Color Temperature FAQ
The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable color to that of the light source. Color temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, manufacturing, astrophysics, horticulture, and other fields. In practice, color temperature is meaningful only for light sources that do in fact correspond somewhat closely to the radiation of some black body, i.e., those on a line from reddish/orange via yellow and more or less white to blueish white; it does not make sense to speak of the color temperature of, e.g., a green or a purple light. Color temperature is conventionally expressed in kelvins, using the symbol K, a unit of measure for absolute temperature.
Color temperatures over 5000 K are called cool colors (bluish white), while lower color temperatures (2700–3000 K) are called warm colors (yellowish white through red).Warm in this context is an analogy to radiated heat flux of traditional incandescent lighting rather than temperature; the spectral peak of warm-coloured light is closer to infra-red and most natural warm-coloured light sources emit significant infra-red radiation. The fact that warm lighting in this sense actually has a cooler color temperature often leads to confusion.
CRI or Color Rendering Index
The CRI is the measure of the ability of a light source to reproduce colors of various objects compared to an ideal light source such as incandescent (only because it’s what our eyes are used to) or natural light. The scale is from 0-100, and those lights with a CRI closer to 100 have an ability to show truer colors across a wide spectrum. It’s important to consider for some applications, but definitely not for all. For example, it’s very important in a retail store to have lights with a high CRI, so that colors appear as they truly are. Whereas in a factory (CRIs often in the 70s or 80s), or with street lamps (CRIs in the 30s or 40s), color accuracy isn’t nearly as important as the overall amount of light produced; or lamp cost.