Lighting for a clean key

Spill is not a grading problem. By the time it reaches the grade it is already someone else's problem, and they will charge you for it.

Distance first

Before you touch a lamp, move your subject away from the wall. Six feet is a starting point; ten is better if the room allows it.

Everything else on this list is easier at ten feet and harder at three. If you take one thing from this, take the distance — it is free, and it does more than any single fixture.

Light the wall on its own

Two soft sources at forty-five degrees, aimed across the wall rather than at it, will get you flat enough. Meter it and walk it: the difference between the brightest and darkest patch should be inside a stop.

Do not light the wall with the same instrument that lights your subject. It is tempting when you are short on lamps, and it produces a wall that is bright in one place and dying in another.

Then light the subject

Key, fill, and — the one people skip — a backlight. The backlight is what separates hair from background. Without it the key has to guess where the subject ends, and it guesses green.

Keep the key off the wall. Flag it if you have to. A subject lit at the right level against a wall lit at the right level is a clean key; a subject lit by the wall's light is a rotoscoping invoice.

Check it on the day, not in post

Pull a rough key on set. Any camera, any laptop, thirty seconds. You are not looking for a finished composite — you are looking for the edges of hair and the shoulders of a dark jacket.

If those hold, the grade will be routine. If they do not, you have a lamp and ten minutes to fix something that will otherwise cost days.