Key Light

What this is about

Every lighting setup starts with one question: where does the key come from. Its angle writes the shadow across a face, its height decides whether eye sockets stay open, its size decides whether the shadow edge is a line or a gradient. Everything added afterwards is a reaction to that choice. The DP calls the key position, the gaffer builds it, and the AC meters it to confirm the working stop.

A term only helps when everyone on set means the same thing by it — so what follows is how it is used, not a dictionary definition.

What runs differently here

Where this differs from the general case:

• The key is defined by dominance, not by hardware — a window, a fire or a phone screen can be the key of a shot.
• Its angle and height are continuity information and belong in the lighting notes, not only in the gaffer's memory.
• Metering the key gives the working stop; every other unit in the setup is then measured in relation to it.

With TillyGen

TillyGen's lighting notes record the key position per setup, so a scene resumed on another day rebuilds the same geometry from the plan.

Change one constraint and the consequences travel through the whole plan: affected shots are flagged, the call sheet is regenerated, and nobody keeps working from yesterday's version.