Color temperature, white balance, and matching your lights

What is color temperature?

Every light source emits light at a particular color temperature, measured in Kelvin (K). The lower the number, the warmer (more orange) the light. The higher the number, the cooler (more blue).

A few reference points:

The cinema industry standardized on two main values: 3,200 K (tungsten) and 5,600 K (daylight). Most professional fixtures let you switch between those two modes, and many modern LEDs are continuously variable.

What white balance does

A camera doesn't know what color the light is. By default, it captures whatever color hits the sensor. White balance (WB) is the camera's correction: you tell the camera what color the light is, and it shifts the image so that white things actually look white in the recording.

If your white balance is set to 3,200 K but you're shooting under 5,600 K daylight, the camera assumes the light is warmer than it actually is — so it shifts the image toward blue. Everything looks cold. The reverse (5,600 K WB under tungsten) makes everything orange.

The simple rule

Match your camera's white balance to the dominant light source.

• Shooting outside at noon? Set WB to ~5,600 K (daylight).
• Shooting inside under household bulbs? ~3,000 – 3,200 K (tungsten).
• Mixed light (window plus a tungsten lamp)? Pick the source that's lighting your subject and match that. Or — better — change one of the light sources so they match each other (see below).

If your camera supports it, custom white balance is the most accurate option: hold up a white or neutral-gray card, fill the frame with it, and let the camera read the exact color of the light. Pros use this constantly because mixed light or unusual sources (sodium vapor parking lot lights, gas-discharge bulbs, mixed LEDs) defeat the preset values.

Mixed light is the enemy

The single most common color problem on indie sets is mixed color temperature — for example, daylight coming through a window competing with a tungsten lamp in the corner of the room.

You have three options when you're stuck with mixed light:

1. Match the lights to each other. This is the cleanest. If you can, gel (cover with a colored translucent sheet) your tungsten fixtures with CTB (color temperature blue) to convert them to daylight. Or gel daylight fixtures with CTO (color temperature orange) to convert them to tungsten. Cinema gel rolls (Rosco, Lee) are inexpensive and one roll lasts forever.

2. Match the windows to the lights. Tape or clip CTO gel on the window glass to convert daylight coming in to match your tungsten fixtures inside.

3. Choose one and live with the contrast. If you can't fix it, decide which source is "correct" and let the other one fall warm or cool. This can look intentional — warm window light pouring in vs. cool office fluorescents, for example. Just make sure it reads as a deliberate choice and not an accident.

A few practical truths

• Mixed white-LED quality varies a lot. Two LEDs both labeled "5,600 K" can look noticeably different. Modern professional LED fixtures publish a CRI (color rendering index) and ideally a TLCI (television lighting consistency index) score — both above 95 is what you want. Cheap LEDs can score under 80 and produce ugly, muddy skin tones.
• Skin tone is what your audience will judge. Get skin right and most other color problems become tolerable. Get skin wrong and nothing else can save the shot.
• Shoot a gray card or color chart on every setup. Hold a gray card up at the start of each take while the camera rolls for one second. In post, your colorist (or you) can use that frame to nail neutral color before any creative grading.

Common mistakes

• Auto white balance for video. AWB is for stills. In video, it drifts as the subject moves or someone walks past — your background color literally shifts mid-shot. Always set a fixed WB.
• Forgetting to switch WB between scenes. You walked from a daylit lobby into a tungsten interior and forgot. Everything is orange now. Set a phone reminder if you have to.
• Bouncing into a colored wall. Bouncing daylight off a yellow wall to make a fill light gives you a yellow fill. Bounce off neutral surfaces (white, gray, or specifically a "color-correct bounce" like Ultra-bounce) when color matters.
• Trusting "5,600 K" labels at face value. Test your fixtures against each other on a white card before the shoot. Adjacent fixtures should look identical.

What to practice this week

Set up a white card or piece of white paper. Shoot ten seconds of it under three different light sources — a window, a household lamp, an overhead fluorescent (or whatever you have). Set your camera to a fixed WB of 5,600 K for all three shots. Then 3,200 K for all three. Watch the recordings back and you'll have an immediate, visual education in how white balance works.

Then go back and white-balance correctly for each. Notice how skin tones settle into "right" instead of "orange" or "blue." That's the win.