Colour Temperature
A measure of the colour of a light source, expressed as the temperature of a theoretical black body radiating the same hue.
Measured in
K (kelvin)
In depth
The scale runs counter-intuitively: low numbers are warm and orange, high numbers are cool and blue, because a heated metal glows red before it glows blue-white. It describes only the blue-to-orange axis, which is why a second control for green-magenta tint is always needed alongside it.
Examples in practice
Candlelight sits near 1900 K, tungsten near 3200 K, midday sun near 5500 K and open shade near 8000 K.