Design Nomenclature / Light & Optics
Kelvin
Also called K, correlated colour temperature, CCT, colour temperature (of a source)
- Light & Optics
- Color
- 2D & 3D
This entry has not been translated yet and is shown in English.
The temperature of the blackbody whose emission a source's colour most nearly matches — 1,900 K for candlelight, 5,500 for midday sun, 6,500 for the D65 white point. Higher numbers are bluer, which inverts the everyday sense of warm and cool.
In practice
A single number collapsing a two-dimensional chromaticity, so it says nothing about a spectrum's gaps. Two lamps rated at the same CCT can render a red wall completely differently.
Not to be confused with
- Color temperatureThe temperature of a blackbody radiator whose color matches the light in question, given in kelvin. It runs backwards from intuition: 2700K is warm orange, 6500K cool blue. Only sources near the Planckian locus have a true color temperature; LEDs and fluorescents get a correlated one, which hides any green or magenta tint the number never reports.
- White balanceThe decision about which spectrum in a scene should record as neutral, and the per-channel scaling that makes it so. It models the eye's own chromatic adaptation in software: get it wrong and everything tints, get it deliberately wrong and a scene turns cold on purpose.
Origin
After William Thomson, Lord Kelvin. A thermodynamic scale borrowed for light because incandescent sources genuinely are hot bodies; LEDs are not, which is why their rating is only 'correlated'.