The correlated colour temperature CCT is a measure for describing the quality of light sources. It indicates the equivalent temperature that a black body radiator would need to have in order to produce light of the same colour.
Blackbody Radiation for several CCTs
Confusingly enough, the concept of a colour temperature is somewhat contrary to what we would describe as 'warm' or 'cold' colours. The light produced by an incandescent lamp, for instance, has a low colour temperature, whereas daylight has a very high one. This is because when a body is heated up, its light goes through red, orange, yellow, white and finally blue as it becomes hotter and hotter.
| CCT | CCT class |
|---|---|
| below 3,300K | warm |
| 3,300...5,300K | intermediate |
| above 5,300K | cold |
Classes of correlated colour temperature
The way we feel when put into an environment with a dominant CCT class depends on the brightness of the room. The higher the illuminance, the more comfortable we feel with cool colour temperatures.
| Illuminance (lux) | Colour of light sources | ||
|---|---|---|---|
| warm | neutral | cold | |
| Emotional response | |||
|
below
500
| pleasant | neutral | cold |
|
500...1,000
| |||
|
1,000...2,000
| stimulating | pleasant | neutral |
|
2,000...3,000
| |||
|
above
3,000
| un-natural | stimulating | pleasant |
The emotional reponse depends on the ambient illuminance level