Colour temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, manufacturing and other fields. Colour temperature is conventionally stated in units of absolute temperature, kelvin (K).
Higher colour temperatures (5,000 K or more) are called cool colours (blueish white); lower colour temperatures (2,700–3,000 K) are called warm colours (yellowish white through red).
In the categorisation of light sources, such as fluorescent lamps, many sources emit light primarily by processes other than thermal radiation. This means the emitted radiation does not follow the form of the visible spectrum. These sources are assigned what is known as a correlated colour temperature (CCT). CCT is the colour temperature of this radiation which to human colour perception most closely matches the light from the lamp.