What "color temperature" actually means
Color temperature is a way of describing the warmth or coolness of a light source. It's measured in Kelvin (K) and originates from the physics of how an idealized object — a "black body" — glows as it gets hotter. Counter-intuitively, lower Kelvin values are warmer in appearance (yellow, orange, red), and higher Kelvin values are cooler (blue, white-blue). A candle is around 1800K. The midday sun is around 5500K. An overcast sky can climb to 10,000K.
When to care about color temperature
Common reference points
- 1700K — candle flame. Deep amber, very warm, almost orange.
- 2400K — sunrise / sunset. Warm golden hour quality.
- 2700K — classic incandescent bulb. The "old-school warm" people often miss when switching to LEDs.
- 3000K — soft white LED. Slightly cooler than incandescent but still distinctly warm.
- 3500K — warm-leaning neutral. Used in hallways, kitchens, retail.
- 4000K — neutral white. Workspace and bathroom default.
- 5000K — daylight. Approximates noon sunlight; great for visual clarity.
- 6500K — bright daylight. Computer monitor default; also the "D65" reference white.
- 10000K — overcast sky / shade. Distinctly blue cast.
Sleep tip: Anything below 3000K in the evening is sleep-respectful. Above 4000K, especially with significant blue content, your circadian system reads "still daytime." See our colors guide for which Night Light X color matches each temperature.
How this tool computes color
The Kelvin-to-RGB conversion uses a well-known approximation derived from black-body radiation curves. It's accurate enough for visualization and bulb-shopping purposes — color science software uses more elaborate spectral calculations, but for "what does 3500K actually look like," this is a great approximation.