Understanding Color Temperature

Color temperature describes the hue of a light source by comparing it to an ideal blackbody radiator. Cooler light appears bluish and has a higher temperature, while warmer light looks orange or red. Photographers, videographers, and lighting designers rely on this measurement to balance scenes. A candle might burn around 1800 K, whereas midday sun can reach 5500 K or more. Awareness of these values helps match different lights and keep colors consistent when moving from one environment to another.

Kelvin and the Visible Spectrum

The Kelvin scale dates back to the 19th century and ties temperature to the glow of heated objects. As a filament or bar of metal rises in temperature, it first glows a dim red, then orange, yellow, and eventually white or even blue. Scientists plotted these colors along a path called the Planckian locus. Our eyes interpret these changes as shifting warmth or coolness. The range between 1000 K and 40,000 K covers nearly all practical lighting situations in photography and cinematography.

The Mired Scale

While Kelvin is convenient, small changes in low temperatures produce more noticeable shifts than the same changes at high temperatures. To account for this perception, cinematographers often use mireds, or micro reciprocal degrees. Mired values are the inverse of Kelvin multiplied by a million. A daylight-balanced bulb around 5600 K converts to about 179 mireds. This representation spreads the differences more evenly across the range of human vision, making it easier to calculate filter strengths for correction gels.

Converting Between Kelvin and Mired

The conversion is straightforward. Mired value equals one million divided by the temperature $T$ in kelvin:

To go back from mireds to kelvin, simply invert the equation:

This calculator performs the first of these conversions, but you can easily rearrange it for the reverse if you need to match filters or gels in the field.

Approximate RGB Values

Digital imaging devices represent colors using combinations of red, green, and blue. Converting kelvin to these RGB values lets you preview how light of a given temperature will appear on screen. The relationship is not perfectly linear, but a widely used approximation models how each channel brightens as temperature increases. Below about 6600 K, red stays nearly saturated while green climbs with the logarithm of temperature. Blue only begins to show prominently above 2000 K. For hotter sources, both red and green taper off following negative power laws. After calculating all three channels, the values are clamped between 0 and 255 for display.

Applications in Photography

Mixed lighting is a common challenge when photographing indoors. Tungsten bulbs glow around 3200 K, but daylight from a window may be closer to 5500 K. If your camera is set for the warmer light, everything near the window takes on a blue cast. Conversely, using a daylight balance makes incandescent lamps look orange. Knowing how to convert and compare color temperatures helps you choose gels for your fixtures or adjust the white balance in your camera. Some artists also exploit these differences creatively to evoke certain moods or times of day.

Example Conversion

Suppose you measure a vintage filament bulb at 2700 K. Using the formula above, the mired value is . The calculator also produces approximate RGB values. In this case, the red channel is near its maximum, the green channel is moderate, and blue is quite low. The resulting color appears warm and amber, exactly what you'd expect from household lighting.

Table of Common Light Sources

Source	Kelvin	Mired
Candle Flame	1800	556
Tungsten Bulb	3200	312
Midday Sun	5500	182
Overcast Sky	6500	154
Clear Blue Sky	12000	83

Limitations and Real-World Considerations

Real light sources often deviate from ideal blackbody behavior. Fluorescent lamps, LEDs, and discharge tubes produce spikes in their spectra that a single number cannot capture. Still, color temperature remains a useful shorthand. When exact accuracy matters, use a color meter that measures multiple wavelengths and calculates precise chromaticity coordinates. For everyday photographic work, the kelvin and mired scales provide a fast and effective way to match equipment. Keep in mind that screens and printers may interpret RGB values slightly differently, so the conversion here should be considered an approximation rather than a guarantee.

Historical Perspective

The idea of characterizing color by temperature arose in the early days of thermodynamics. William Thomson, later known as Lord Kelvin, formalized the absolute temperature scale in the 1840s. By the early 20th century, engineers studying incandescent lamps used the concept to classify bulbs. Cinematographers adopted it to plan filter selections and unify multiple light sources on set. Today the concept extends beyond film and photography into astronomy, horticulture, and even computer display calibration. Understanding this terminology builds a bridge between art, science, and practical lighting design.

Conclusion

This Color Temperature Converter quickly translates a Kelvin value into mireds and offers an estimated RGB color. Use it to determine gel strengths, set camera white balance, or simply visualize how warm or cool a light source appears. Because the calculation runs entirely in your browser, you can experiment with different temperatures without sending data anywhere. Whether you're lighting a portrait, designing theatrical scenery, or calibrating a monitor, mastering the relationship between Kelvin and color opens up new creative possibilities.