What Kelvin measures
Heat a piece of metal and it glows: dull red at first, then orange, yellow, white and eventually bluish white. Physicists model this with an ideal "black body", and color temperature is the temperature of a black body whose glow matches a given light, measured in kelvins (K).
The counterintuitive part is that low numbers look warm and high numbers look cool. A candle at about 1,850 K is orange, midday sun around 5,500 K is close to neutral white, and a clear blue sky can exceed 10,000 K. Photographers and lighting designers say "warm" and "cool" in the artistic sense, even though warm light comes from the colder source.
Light sources at a glance
| Source | Approx. K | On screen |
|---|---|---|
| Candle flame | 1,850 | #FF8100 |
| Incandescent bulb (60 W) | 2,400 | #FF9B3D |
| "Warm white" LED | 2,700 | #FFA757 |
| Halogen | 3,000 | #FFB16E |
| Neutral office light | 3,500 | #FFC18D |
| Cool white fluorescent | 4,100 | #FFD0AB |
| D50 print-viewing standard | 5,000 | #FFE4CE |
| Midday sun, camera flash | 5,500 | #FFEDDE |
| D65, the white point of sRGB screens | 6,500 | #FFFEFA |
| North-sky shade | 7,500 | #E6EBFF |
| Clear blue sky | 10,000 | #CADAFF |
The table in the tool also lists a match flame at 1,700 K. Click any Kelvin value there to jump the slider to it.
How the RGB values are calculated
The tool uses Tanner Helland's widely used curve fit, which approximates published black-body color data with a handful of logarithm and power formulas. It covers 1,000 K to 40,000 K and is accurate to within a few percent, plenty for design mockups. Below 6,600 K, red is held at 255 and green and blue rise with temperature. Above it, blue stays at 255 while red and green fall.
The results are display colors, normalized so the brightest channel is 255. They show the tint of the light, not its brightness: a candle isn't as bright as the sun, but both appear here at full intensity.
The "white page" preview
The panel under the readouts multiplies an off-white paper color (#FAF8F3) by the light color. That's roughly what a camera with its white balance fixed at daylight records: paper under a 2,700 K bulb comes out amber, and in shade at 7,500 K it turns blue. Our eyes adapt and see both as white, which is exactly why cameras need a white-balance setting.
Estimating the Kelvin of a color
Enter a color in the second panel to get its correlated color temperature (CCT) using McCamy's 1992 formula. The formula converts the color to CIE xy chromaticity and finds the nearest point on the black-body curve. Some examples:
#FFD6AA, a soft peach, is about 4,100 K.#FFFFFFon an sRGB screen is about 6,500 K, which is the D65 white point.#CCDDFF, a pale sky blue, is about 9,700 K.
The result only means something for near-white colors. Saturated colors like a strong green aren't on the black-body curve at all, and the tool tells you when an estimate is meaningless or only rough.
Uses
- Lighting mockups: tint a room render or product shot to show warm versus cool bulbs.
- Design themes: warm, sepia-like "night mode" tints are around 3,000–3,400 K.
- Photography: understanding white-balance presets (tungsten about 3,200 K, daylight about 5,500 K, shade about 7,500 K).
- Choosing bulbs: 2,700 K for cozy living rooms, 3,000–4,000 K for kitchens and offices, 5,000 K and up for workshops and color-critical tasks.
Related tools
To see the result in every color format, paste the HEX code into the color converter. The gradient generator can turn two temperatures into a sunrise sky. To check how warm and cool light mix, try the color mixer.
FAQ
Is 5000 K or 6500 K "daylight"?
Both are used. D50 (about 5,000 K) is the standard for judging print, and D65 (about 6,500 K) is the standard for screens and average daylight. Bulbs sold as "daylight" are usually 5,000–6,500 K.
Does a higher Kelvin mean brighter light?
No. Brightness is measured in lumens. Kelvin describes only the color of the light.
Why is 6500 K not perfectly white here?
The fit gives #FFFEFA, a hair warm, because it's an approximation. Exact D65 is defined as the white of sRGB, #FFFFFF.