Color Temperature Converter
Convert a colour temperature in Kelvin to its RGB colour, with lighting presets from candlelight to overcast sky, and why higher numbers look cooler.
What color temperature means
Kelvin describes the colour of light, from the orange glow of a candle near 1900 K, through household warm white at 2700 K, up to the blue of open sky past 9000 K. Counter-intuitively, higher Kelvin means cooler-looking (bluer) light. Photographers match white balance to it; lighting designers pick bulbs by it.
"Warm" light is the cold end of the scale
Colour temperature is the temperature a black body would need to be to glow that colour. Heat something up and it goes red, then orange, then white, then blue — so bluer light always means a hotter source. The everyday vocabulary runs the other way, because orange feels warm:
| Temperature | Source | Colour | Called |
|---|---|---|---|
| 1900K | candle flame | #ff8400 | warm |
| 2700K | incandescent bulb | #ffa757 | warm |
| 3200K | studio tungsten | #ffb87b | warm |
| 4100K | moonlight | #ffd0ab | warm |
| 5000K | horizon daylight | #ffe4ce | warm |
| 5500K | midday sun | #ffedde | warm |
| 6500K | overcast daylight | #fffefa | warm |
| 7500K | blue sky shade | #e6ebff | cool |
| 10000K | clear blue sky | #cadaff | cool |
A candle at 1900K is artistically the warmest thing on the list and physically the coldest; a clear sky at 10000K is the coolest-looking and five times hotter. Both usages are correct and neither is going to give way, which is why "warmer" is ambiguous in a photography setting and the number is the safer thing to say. A 2700K bulb is unambiguous; a "warm white" bulb is a marketing phrase.
The crossover sits at 6600K, where all three channels reach 255 and the output is
exactly rgb(255, 255, 255). Below it red leads; above it blue does.
The output is a hue, not a brightness
Worth knowing before using any of these numbers. Sampling 281 temperatures from 1000K to 15000K, every single one has at least one channel pinned at 255. Not most — all of them.
| Channel pinned at 255 | Of 281 samples |
|---|---|
| red | 114 |
| green | 2 |
| blue | 169 |
That is not a defect. Colour temperature describes the chromaticity of a light: what colour it is, not how much of it there is. A candle and a floodlight at the same temperature emit the same ratio of red to blue, and the formula normalises so the brightest channel is full. If you want a dim warm light you scale the result yourself — the temperature cannot tell you.
Green is the interesting row: it is pinned 2 times, only right at the neutral point where all three reach 255 together. Everywhere else it sits below the leader, which is what makes the ramp a smooth orange-to-blue rather than a jump.
The practical consequence is that you cannot compare two swatches from this tool for brightness. They are all as bright as they can be, which is exactly what makes them comparable as colours and useless as intensities.
And the neutral point is 96K off
sRGB defines its white point as D65, about 6504K. A perfect conversion would give exactly equal channels there:
| Temperature | Output | Channel spread | |
|---|---|---|---|
| sRGB white point | 6504K | rgb(255, 254, 250) | 5 |
| most neutral here | 6600K | rgb(255, 255, 255) | 0 |
This approximation is most neutral at 6600K instead — 96K high. At D65 itself it gives a spread of 5 out of 255, which is invisible and worth knowing anyway: the formula is a curve fit to sampled blackbody data rather than a derivation, so it is accurate to around a per cent and exact nowhere.
It is at least well behaved. Sweeping the whole range, red never increases with temperature and blue never decreases — no reversals, no kinks. That is the right trade for picking a light bulb and the wrong one for calibrating a monitor.
How to use
- Set a temperature in Kelvin, or pick a preset.
- Read the resulting colour.
- Compare against the reference lighting conditions.
- Match your lighting before judging colour accuracy.
Frequently asked questions
Why is a higher temperature called cooler?
Because the naming follows physics rather than psychology. A heated object glows red at lower temperatures and blue-white at higher ones, so the Kelvin figure genuinely describes how hot the emitter is. We happen to associate blue with cold and orange with warmth, which puts the everyday language exactly backwards.
What are the common values?
Candlelight is around 1,900 K, a traditional incandescent bulb about 2,700 K, and warm white LEDs match that. Neutral white is around 4,000 K, direct midday sunlight about 5,500 K, and overcast sky or shade can exceed 7,000 K, which is why photographs in shade look blue without correction.
What is white balance?
The camera's correction for the colour of the light. Our eyes adapt automatically, so white paper looks white under a warm bulb and under daylight; a camera does not, and records the actual cast. Setting white balance tells it which light to treat as neutral.
Which colour temperature should I choose for a room?
Warmer light, around 2,700 to 3,000 K, suits living spaces and evening use, and matches what people expect from domestic lighting. Cooler light around 4,000 K and above suits kitchens, workshops and workspaces where alertness and detail matter more than atmosphere.
Does colour temperature affect sleep?
Blue-rich light in the evening does suppress melatonin, and screens and cool white lighting both provide it. The practical response is warmer light and lower brightness in the hours before bed, which most devices now offer automatically.
What is the colour rendering index?
A separate measure of how faithfully a light source shows colours, on a scale to 100. It is independent of temperature — two bulbs at the same Kelvin can render colours very differently. Low-index lighting makes skin and fabrics look wrong, which is why it matters in shops, studios and bathrooms.
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