<Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (June 2012) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (June 2012) (Learn how and when to remove this template message) </Td> </Tr> <P> The color temperature of a light source is the temperature of an ideal black - body radiator that radiates light of a color comparable 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 kelvin, using the symbol K, a unit of measure for absolute temperature . </P> <P> 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 infrared, and most natural warm - coloured light sources emit significant infrared radiation . The fact that "warm" lighting in this sense actually has a "cooler" color temperature often leads to confusion . </P>

What is the k rating of a light bulb