Home · Published 2026-04-01 · Updated 2026-07-20
Understanding Colour Temperature: A Complete Guide
2700K, 4000K, 6500K — what do these numbers actually mean, and which should you use where?
3 min read
ICBy Imogen ClarkeEditorial contributor
TL;DR
What Colour Temperature Describes
Correlated colour temperature is expressed in kelvin (K). Lower values generally describe a warmer, more yellow appearance, while higher values describe a cooler, bluer appearance. Kelvin does not tell you how bright a lamp is or how accurately it renders colours.
Choose for the Task and the Space
There is no single correct colour temperature for every bedroom, kitchen, bathroom, or office. Warmer light is often chosen for relaxed settings, while neutral or cooler light may be preferred for visually demanding tasks. Daylight, wall colours, materials, and individual preference can change how the same lamp appears, so compare options in the actual space when possible.
Check Colour Rendering Separately
Colour rendering and colour temperature describe different qualities. CRI indicates how a source renders colours relative to a reference, and higher values generally indicate a closer match. Check the product's CRI alongside lumen output, efficiency, and dimmer compatibility rather than treating kelvin as a complete measure of light quality.
When Tunable White Helps
Tunable-white lamps let users change the appearance of white light for different activities or preferences without replacing the bulb. Schedules can automate those changes, but colour temperature alone does not establish a particular sleep, alertness, or health outcome.
Sources
- 1Purchasing Energy-Efficient Light Bulbs
U.S. Department of Energy
- 2Downlights: Key Product Criteria
ENERGY STAR