The Kelvin (K) is a unit of temperature measurement starting from absolute zero at -273 Celsius. Degrees Kelvin (or color temperature) is used in color photography to indicate the color balance or spectrum of light emitted from a light source. If you were to heat a chunk of iron to 3000Âº Kelvin, the light emitted from the iron (a dull red glow) would be said to have a color temperature of 3000K for the purposes of color photography. Sunlight measures about 5500K and film balanced for sunlight (daylight film), will assure ‘true’ color rendition for objects reflecting the sun. Photographic, or Xenon, flash creates a light source with a color temperature of about 6000K. AlienBee flash units come with a standard flash tube which measures 5600K, and is daylight-balanced for film. We also offer optional UV-coated tubes, rated at 5200K.