Kelvin (K) is the SI unit of absolute temperature that photographers use to express the color temperature of light. In color and white balance for photography, a Kelvin value describes how warm or cool a light source looks: lower values such as 2,700 K are orange, and higher values such as 7,000 K are bluish. Cameras use Kelvin settings to tell the white balance system what kind of light illuminates the scene.
The scale is named after the physicist William Thomson, Lord Kelvin. It is written without a degree sign, so the correct form is 5,500 K, not 5,500 °K.
Why light color is measured in Kelvin
The link between temperature and color comes from the ideal black-body radiator. As a black body is heated, it glows first dull red, then orange, yellow, white and finally bluish white. The color temperature of a light source is the temperature of the black body whose glow matches that light most closely.
This creates an apparent paradox: higher Kelvin values look cooler in everyday color language, even though they correspond to hotter radiators. The table lists typical sources and their approximate values.
| Light source | Approximate value | Visual impression |
|---|---|---|
| Candle flame | About 1,800 to 1,900 K | Deep orange |
| Household tungsten bulb | About 2,700 to 2,900 K | Warm yellow-orange |
| Studio tungsten halogen | About 3,200 K | Warm, film standard |
| Sunrise or sunset light | About 2,500 to 3,500 K | Golden |
| Midday sun | About 5,000 to 5,500 K | Neutral white |
| Electronic flash | About 5,500 to 6,000 K | Neutral to slightly cool |
| Overcast sky | About 6,500 to 7,500 K | Cool |
| Open shade under blue sky | About 7,500 to 10,000 K | Distinctly blue |
Correlated color temperature and its limits
Only incandescent sources follow the black-body curve closely. Fluorescent tubes, LEDs and discharge lamps emit light with a different spectral distribution, so their value is given as a correlated color temperature (CCT): the nearest point on the black-body curve.
A Kelvin value describes only the warm-to-cool axis. Deviations toward green or magenta are expressed separately as tint, often on a Duv or green-magenta scale. Two lamps with the same CCT can therefore look different on camera, and their color rendering can differ even more.
| Property | Described by Kelvin | Separate measure |
|---|---|---|
| Warm to cool balance | Yes | Not needed |
| Green to magenta shift | No | Tint or Duv |
| Spectral quality | No | Color rendering indices such as CRI or TLCI |
| Brightness | No | Lux or exposure value |
Kelvin values and white balance settings
In a camera, the Kelvin setting tells the white balance system what light color to neutralize. Setting the camera to 3,200 K tells it the light is warm, so it adds blue to render white objects white. A common confusion is that a higher Kelvin setting makes the image warmer, because the camera compensates for an assumed cooler light.
| Actual light | Camera setting | Result in the image |
|---|---|---|
| Tungsten at 3,200 K | 3,200 K | Neutral whites |
| Tungsten at 3,200 K | 5,500 K | Strong orange cast |
| Daylight at 5,500 K | 3,200 K | Strong blue cast |
| Shade at 7,500 K | 5,500 K | Cool, bluish result |
| Shade at 7,500 K | 7,500 K | Neutral whites |
Most cameras accept settings from about 2,500 K to 10,000 K in steps of 100 K. For precise results, a custom white balance from a gray card or a color checker is more reliable than estimating the Kelvin value by eye, especially under mixed or artificial light.
Mireds and correcting light with filters
Equal Kelvin steps do not produce equal visual changes. A shift from 2,700 K to 3,200 K looks much larger than a shift from 6,500 K to 7,000 K. For this reason, lighting technicians use the mired scale, calculated as one million divided by the Kelvin value.
Color correction gels are rated in mireds. A full CTO gel converts daylight to roughly tungsten color, and a full CTB gel does the reverse. Matching flash or LED sources to ambient light with gels prevents mixed color casts that no single white balance setting can fix.
| Kelvin value | Mired value | Typical context |
|---|---|---|
| 2,700 K | About 370 | Domestic warm white |
| 3,200 K | About 313 | Tungsten studio light |
| 4,000 K | 250 | Neutral white LED and office light |
| 5,600 K | About 179 | Daylight balanced light |
| 6,500 K | About 154 | Display white point D65 |
Common misconceptions about Kelvin
- Higher Kelvin means warmer light is false; higher values describe cooler, bluer light.
- Kelvin alone defines light color is false; tint and spectral quality also matter.
- Daylight is always 5,500 K is false; daylight ranges widely with time, weather and shade.
- Correct Kelvin always means correct color is false; mixed sources need gels or local correction.
In simple terms
Kelvin is the number photographers use to describe whether light looks warm or cool. Candlelight and old light bulbs have low numbers and look orange, while cloudy daylight and shade have high numbers and look blue.
Cameras use this number to correct colors so that a white shirt looks white under any light. Telling the camera the right Kelvin value is like telling it what kind of lamp is shining on the scene.
A practical example
A corporate photographer shoots executive portraits in a meeting room lit by warm ceiling spots of about 3,000 K, while a large window adds daylight of about 6,000 K. With auto white balance, faces look orange on one side and blue on the other.
She places a full CTO gel on her flash to bring it near 3,200 K, closes the blinds and sets the camera to 3,200 K. A test frame with a gray card confirms neutral whites. The portraits show natural skin tones and consistent color across the whole series, which saves hours of local correction in editing.