Color Temperature (Kelvin) Converter
Drag the slider (or type an exact value) to see the approximate RGB color that corresponds to a given color temperature, in degrees Kelvin. Useful for photographers, lighting designers, and anyone matching screen or bulb color to a target white balance.
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About Color Temperature
Color temperature describes the color of light emitted by an idealized "blackbody radiator" heated to a given temperature, measured in Kelvin (K). At low temperatures the emitted light is deep orange-red; as temperature rises it shifts through yellow-white to blue-white. This is the same physical basis used to describe the "warmth" or "coolness" of light bulbs, daylight, and camera white-balance settings.
The Approximation Formula
Rendering true blackbody colors requires integrating a full emission spectrum against the CIE 1931 color-matching functions — too slow for an interactive tool. This converter instead uses the widely published Tanner Helland approximation, a curve-fit algorithm that reproduces the same visual result to a close degree for temperatures between roughly 1000K and 40000K. Given \( T \) in hundreds of Kelvin (\( T = K / 100 \)), the red, green, and blue channels are computed piecewise:
\[ \text{Red} = \begin{cases} 255 & T \le 66 \\ 329.698727446 \times (T-60)^{-0.1332047592} & T > 66 \end{cases} \]
\[ \text{Green} = \begin{cases} 99.4708025861 \times \ln(T) - 161.1195681661 & T \le 66 \\ 288.1221695283 \times (T-60)^{-0.0755148492} & T > 66 \end{cases} \]
\[ \text{Blue} = \begin{cases} 0 & T \le 19 \\ 138.5177312231 \times \ln(T-10) - 305.0447927307 & 19 < T < 66 \\ 255 & T \ge 66 \end{cases} \]
Each channel is clamped to the 0-255 range and rounded to the nearest integer. This is a practical approximation commonly used in lighting and photography software, not a full spectral calculation.
Reference Points
The legend below the slider marks well-known real-world sources: candle flame (~1900K), incandescent/tungsten bulbs (~2700K), halogen (~3200K), midday daylight (~5600K), overcast sky (~7000K), and open shade or blue sky (~10000K+). Click any reference point to jump the slider to it.
Frequently Asked Questions
What color temperature is daylight?
Direct midday sunlight is commonly referenced at around 5600K, which is also the standard white-balance setting on most cameras labeled "daylight." Actual daylight varies through the day — sunrise/sunset can drop below 2000K, while a blue sky in open shade can exceed 10000K.
What's the difference between "warm white" and "cool white" LED bulbs?
Warm white LEDs are typically rated around 2700-3000K, matching the yellowish glow of traditional incandescent bulbs. Cool white or "daylight" LEDs are typically rated 5000-6500K, producing a whiter or slightly blue-tinted light.
Why does a higher Kelvin number mean a cooler, bluer color when it sounds like it should be warmer?
This is a naming convention from blackbody physics, not everyday color language. A physical object glows orange-red at lower temperatures and blue-white at higher temperatures — the opposite of how we casually call orange/red "warm" and blue "cool" in design. So high-Kelvin light is physically hotter but visually "cooler" in the everyday sense.
Is this exact enough for professional color-critical work?
No. This tool uses a fast curve-fit approximation intended for design, education, and general reference — it's not a substitute for a calibrated colorimeter or spectrophotometer. Professional photography, film, and display calibration work should rely on measured, hardware-calibrated color data.