White balance and colour temperature explained

Q: Does raising the Kelvin number make the photo warmer or cooler?

Raising the Kelvin setting makes the photo warmer. You are telling the camera the light is very blue, so it adds warmth. That runs opposite to the scale itself, which is why everyone gets it backwards at least once.

White paper reflects very different light at noon, under a tungsten bulb and on a grey day, yet it always looks white to you because your brain corrects for it. The camera can't. White balance tells it how.

An outdoor portrait in warm light with a sunlit background

1. Colour temperature and Kelvin

Colour temperature is measured in Kelvin (K), and it runs backwards from what you might expect: low numbers are orange, high numbers are blue.

A log-scale colour temperature ruler from 1500K to 10500K with candle, tungsten, sunrise/sunset, fluorescent, midday sun, overcast, open shade and clear blue sky marked — Colour temperature of common light sources: lower is more orange, higher is more blue.

Source	Approx. temperature	Looks
Candle	1800K	Deep orange
Tungsten / warm LED	2700–3000K	Yellow
Sunrise and sunset	3000–4000K	Warm
Midday daylight	5500K	Neutral
Overcast	6500–7500K	Bluish
Open shade / blue hour	8000–10000K	Strongly blue

2. What white balance does

Setting white balance tells the camera roughly what temperature the light is, and it adds the complementary colour to cancel the cast. 5500K means "correct for midday sun".

The same waterfall shot in daylight with white balance set to 3200K, 5600K and 7500K: blue, neutral and yellow, each with a grey card showing the cast — One scene, three white-balance settings. The grey card shows the cast most clearly.

Hence the classic mistake: leave it on daylight (5500K) under warm bulbs and the shot comes out yellow, because the camera assumed neutral light. Set tungsten in sunshine and everything goes blue.

Accurate and good-looking are different things. Correct a sunset to dead neutral and the gold disappears. Often you want to keep the colour of the light. White balance is a creative choice too.

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3. When auto white balance fails

Mixed sources. Cool window light, warm lamps inside. The camera splits the difference and neither side looks right.
One colour filling the frame. A field of grass or a red brick wall looks like a cast to the algorithm, and the colours come out washed-out and grey.
Drift across a burst. Reframe slightly and auto picks a new value, so the sequence won't match in batch editing.

4. Handling it in practice

Shooting RAW, don't sweat it on location. White balance is just a tag in the file and changes later at no cost; see RAW or JPEG.
Shooting JPEG, get it right in camera. It is baked into the pixels and only partly fixable. Under steady light, a fixed Kelvin value beats auto.
When colour must be exact, shoot a grey card in the ambient light, click it with the eyedropper in your editor, and apply that to the whole set.
In mixed light, get skin tones right first. A background leaning a little warm or cool is usually fine.

5. FAQ

Does a yellow photo always mean the white balance is wrong?

No. The light may really be warm, at sunset or under warm bulbs, and that may be the mood you want. Check whatever should be white or grey, like a wall or a shirt. If that has a cast, the white balance is off.

Can I just leave it on auto?

For everyday shooting, yes; auto is reliable under a single light source. In mixed light, with one colour filling the frame, or when a set has to match, go manual or use a grey card.

Does raising the Kelvin number make the photo warmer or cooler?

Raising the Kelvin setting makes the photo warmer. You are telling the camera the light is very blue, so it adds warmth. That runs opposite to the scale itself, which is why everyone gets it backwards at least once.