Correlated Color Temperature (CCT)

CCT describes the color appearance of white light, in kelvin, by comparison to an ideal blackbody radiator. Lower values are warmer (2700–3000 K, amber-white), middle values neutral (4000 K), higher values cooler (5000–6500 K, blue-white daylight). Industrial practice: 4000 K for most factory and warehouse interiors, 5000–6500 K where alertness and contrast matter (inspection, security), 2700–3000 K for residential streets and ecologically sensitive areas since warmer light scatters less and attracts fewer insects. CCT does not describe color accuracy — that is CRI — and two fixtures at the same nominal CCT can differ visibly, which chromaticity tolerance (SDCM) controls.

For the application chart from 2700K to 6500K, the 4000K versus 5000K decision and the colour-consistency tolerance worth specifying alongside it, see LED colour temperature.