5500K is photographer shorthand for neutral daylight. It’s the colour temperature of midday sun on a clear day, and the value most flashes, LED panels and HMI bulbs are tuned to. When you see “5500K” on a strobe box, that’s why.
But to actually use that information, you need the Kelvin scale.
The Kelvin scale in 60 seconds
The Kelvin scale measures colour temperature - the colour of light a black object would emit when heated. Lower temperatures glow red-orange (think a campfire); higher temperatures glow blue-white (think a star).
For photographers and filmmakers, lower Kelvin = warmer light, higher Kelvin = cooler light.
Common Kelvin values
| Kelvin | Light source | Looks like |
|---|---|---|
| 1800K | Candle flame, gas lamp | Deep amber |
| 2500K | Sunrise / sunset | Golden orange |
| 2800K | Soft white incandescent bulb | Warm yellow |
| 3200K | Standard tungsten / halogen | Yellow-orange |
| 4000K | Warm fluorescent | Pale yellow |
| 4500K | Cool fluorescent / moonlight | Near-neutral |
| 5000K | Horizon daylight | Slightly warm white |
| 5500K | Midday sun, camera flash, daylight LED | Neutral white |
| 6000K | Overcast sky | Slightly blue |
| 6500K | Cloudy daylight, “daylight” monitors | Cool blue |
| 7500K | Open shade | Blue |
| 10000K+ | Deep blue sky (north light) | Strong blue |
Why 5500K is the reference
Camera sensors and film stock are designed around two anchor points: 3200K (tungsten) and 5500K (daylight). Almost everything else is a deviation from one of those two.
- A daylight-balanced light source = 5500K.
- A tungsten-balanced light source = 3200K.
- A bi-colour LED panel = adjustable between 2700K and 6500K.
When you set a camera’s white balance to “Daylight,” you’re telling it to assume the light is 5500K. If you light the scene with HMI or daylight LEDs (both 5500K), white objects render white. If you light with tungsten at 3200K but leave WB on Daylight, white objects render orange on the sensor.
How to find the actual Kelvin of a scene
You don’t have to guess. Point a phone-based meter at the scene and read the number.
- Install KEV - White Balance Meter AI on your iPhone or iPad.
- Open the app, aim the rear camera at the light source or the subject.
- The Kelvin value (plus magenta/green tint) updates in real time.
Then dial that exact Kelvin into your camera’s custom white balance.
Full step-by-step → How to measure color temperature with your iPhone
Why the scale runs backwards
Everyone trips over this once: 3000K is called warm and 7000K is called cool, which is the opposite of how temperature normally works.
The numbers are real temperatures - just not of the light. They describe how hot you would have to heat an idealised black object before it glowed that colour. A bar of iron at 1000 K glows dull red. Push it to 3000 K and it glows the yellow-orange of a household bulb. At 5500 K it glows white. Past 7000 K it glows blue.
So the physics is hotter-equals-bluer. The vocabulary - warm light, cool light - came from painters and interior designers describing how colours feel, and it stuck. Both are correct and they point in opposite directions.
Where 5500K comes from
It is not a round number someone picked. The reference is a CIE standard illuminant called D55, defined to represent average midday sunlight, and its correlated colour temperature works out at roughly 5500K. Its better-known sibling D65 (~6500K) represents average north-sky daylight and is the white point your monitor and every sRGB image is built around.
That is why 5500K and 6500K both turn up constantly and mean slightly different things: 5500K is sunlight, 6500K is daylight including sky. Film stock and strobes standardised on the first; displays standardised on the second.
5500K or 6500K?
| Situation | Set | Why |
|---|---|---|
| Direct midday sun | 5500K | The reference case |
| Overcast, flat grey sky | 6500K | Cloud scatters out the red end |
| Open shade on a sunny day | 7000 - 7500K | Lit by blue sky, not by the sun |
| Studio strobe or daylight LED | 5500K | Manufacturers tune to D55 |
| Grading suite / monitor calibration | 6500K | D65 is the sRGB and Rec.709 white point |
| Interior with daylight through a window | Meter it | Usually lands 6000 - 7000K |
Setting 6500K under 5500K light does not make the light cooler - it makes the image warmer, because you have told the camera the light is bluer than it is and it compensates by adding orange.
What happens when the number is wrong
The direction of the error is worth memorising, because it lets you fix a shot by eye.
| Camera set to | Light actually is | Image comes out |
|---|---|---|
| 5500K | 3200K tungsten | Heavily orange |
| 3200K | 5500K daylight | Heavily blue |
| 5500K | 6500K overcast | Slightly warm |
| 6500K | 5500K sun | Slightly warm |
| 3200K | 2800K bulb | Slightly blue |
The rule underneath: set the camera higher than the light and the image warms; set it lower and the image cools. Some people deliberately dial 300 - 500K above the metered value to warm skin tones. That is a look, not an error - but you only get to make it on purpose if you know the real number first.
Buying bulbs by Kelvin
The same scale is printed on every bulb box, and it is the most useful number there.
| Marked | Called | Suits |
|---|---|---|
| 2700K | Soft white | Living rooms, bedrooms, restaurant warmth |
| 3000K | Warm white | Kitchens, bathrooms, hospitality |
| 3200K | Tungsten / studio | Matching film lights and practicals on set |
| 4000K | Cool white / neutral | Offices, garages, task lighting |
| 5000K | Daylight | Workshops, retail, colour-critical inspection |
| 6500K | Cool daylight | Clinical spaces, plant grow lights |
For anyone dressing a set: buy every practical in a room at the same Kelvin. Mismatched bulbs in one frame is the single most common cause of a shot that will not grade cleanly, and it costs nothing to avoid at the shop.
Tips for using the Kelvin scale on set
- Bi-colour LEDs: match your key light to the practicals. If the room’s tungsten bulbs read 2900K, set your LED to 2900K, not 3200K.
- Magic hour: Kelvin shifts ~200K every five minutes near sunset. Re-meter often.
- Mixed sources: meter each one. Then either gel them to match, or pick a Kelvin between them as a compromise WB.
- Shooting log/RAW: you can fix Kelvin in post, but you cannot fix it if AWB drifted shot-to-shot. Lock it manually.