Filming next to a window

You picked the spot because of the light. It is the brightest corner in the flat, it costs nothing, and on the afternoon you tested it you looked better on camera than you ever have. Then you filmed a series there, and the third video refuses to sit next to the first one. Nothing was moved, no setting was touched, and the footage still does not match.

Daylight is not a light source in the way a lamp is. A lamp is a decision you make once. Daylight is a decision the weather keeps making, and it never mentions having made one. Two changes solve most of this: film at the same hour every time, and leave one lamp on so the daylight is not the only thing holding your exposure up.

Why does the footage not cut together?

Because two shots filmed an hour apart were lit differently, and viewers notice even when they cannot name it.

Cutting works when the shots agree about three basics: how bright the subject is, what colour the light is, and which direction it comes from. Break one and the cut announces itself. Break all three and the video reads as though it came from two separate days, which, in the way that matters, it did.

How daylight drifts

Three things, on three different clocks.

Brightness

The sun moves slowly and cloud moves quickly. A cloud can take most of the light out of a room in seconds and give it back just as fast.

With automatic exposure, the camera may adjust as the light changes. With manual exposure, the settings stay fixed but the recorded brightness can still change during a take. Both need a test when daylight varies.

Colour

Colour temperature is just a way of saying whether a light leans orange or blue. Direct midday sun is fairly neutral, an overcast sky is noticeably bluer, and late sun through a window is warmer and gets warmer as the hour goes on.

So the same chair, in the same room, on the same day, hands you a slightly orange face at one point and a slightly blue one at another. Skin is the one thing every viewer judges without training, which is why this is the change people spot first.

Direction

The sun crosses the sky, so the angle it enters your window at moves with it, and the shadow under your nose that fell one way at eleven falls another way at two. This is the slowest of the three and much the hardest to deal with afterwards, because a shadow that has moved is not a setting. It is geometry, and it was recorded.

Should you sit beside the window or face it?

Face it, or nearly.

Side-on is the default almost everybody lands on, and it gives a bright half and a dark half with a hard line down the middle: more contrast than a face wants, and more than a camera copes with in a room with nothing pale on the shadow side.

Turn your chair until the window sits where a key light would sit, in front of you and off to one side, and you keep the shape while losing the split. Do not put it behind you, though. A window behind your head is a very bright light aimed at your camera, and the camera will expose for the window and leave you as an outline.

Adding one lamp

It puts a floor under the exposure.

The reason to add artificial light to a daylight room is not that daylight looks bad. It is that daylight is unsupervised. A lamp that stays on all session contributes a constant amount, so when the cloud arrives the total light drops by less and when the sun returns it rises by less. The swing shrinks and the clips move closer together, with nothing about the look having to change. It reduces the variation rather than removing it, which is the most you can ask of one lamp.

On one music education partnership, filming happened in classrooms on daylight alone, and inside a single session the footage swung from too dark to blown out. The fix was not to shut the blinds and start again with lamps. It was to add artificial light alongside the daylight, so the daylight stopped being the only thing holding the exposure up.

In this setup, the lamp provides a stable base while daylight supplies part of the look. In another room, controlling or replacing the daylight may be the better choice.

When should you close the curtain and start again?

When the sun is doing something interesting.

Direct sunlight can create a moving bright patch or hard shadow. Exposure and grading may help, but cannot reliably make changing light look identical. Diffuse or block it when continuity requires more control.

Two decent options. Diffuse it: a thin white curtain turns a small hard source into a large soft one, the trick a softbox performs on a lamp. Or shut it out and light the room yourself. Both beat three hours of material that will not cut together.

A window routine you set up once

1. Film at the same time of day, every time. A recurring calendar slot, not a reminder. 2. Sit facing the window rather than beside it, and record thirty seconds from that seat before you mark the position with tape. A bare window is a hard, flat, reflective surface, and Why your video sounds echoey has the fix if you can hear the room in the playback. 3. Set exposure and white balance manually, so the camera stops chasing the weather mid-sentence, and roll a few seconds of a white or grey card at the start as a colour reference to match back to. 4. Leave one lamp on for the whole session, at a level you never adjust. 5. If the sky changes badly, stop and refilm the section instead of pressing on.

If the light changes significantly, check the take while the setup is still available. A short retake may be simpler than matching the change later, though the time needed depends on the material.

Sources and evidence

What here is established colour science, and what is our own routine for a window setup.

What is established. Daylight's colour changes materially through a session with the height of the sun, the cloud and the atmosphere, which is why the same chair, in the same room, hands back a slightly orange face at one point in the day and a slightly blue one at another. The CIE's daylight locus describes the family of daylight chromaticities this variation moves within, rather than a fixed path a day follows by the clock. CIE colorimetry more broadly underpins treating white as a setting a camera has to be told rather than something it senses on its own, which is why manual white balance stops a camera re-deciding it mid-session.

Our method. Facing the window rather than sitting beside it, filming at the same hour each time, and leaving one lamp on to put a floor under the exposure, are this studio's own working routine for a window setup, not a claim that daylight can be fully controlled.

References.

• CIE. Daylight locus (International Lighting Vocabulary 17-23-060). cie.co.at . The daylight locus is the locus of chromaticities of CIE D illuminants parameterised by correlated colour temperature. Not a fixed daily blue-overcast-to-warm-low-sun path; real daylight scatters around it.
• Knoop, M., Weber, N. & Diakite, A. K. Approach to Analyse Seasonal and Geographical Variations in Daylight Illuminants. files.cie.co.at . Daylight illuminant chromaticity and spectrum vary seasonally and geographically; daylight is highly variable.