Every lighting plan is also a plan of shadow. The difference between a room that feels considered and one that feels merely bright is usually what was left dark.
Darkness has a job
Shadow gives the eye somewhere to rest. It tells you where a room ends, which way a wall turns and how far away the garden is. When every surface is lit to the same level, a room loses its depth: the ceiling comes down, the corners disappear, and the view outside becomes a black mirror.
So we start the other way round. Before we place a single fitting, we mark what should stay quiet — a stretch of wall beside a window, the far end of a corridor, the underside of a stair. Those are not gaps in the scheme; they are part of it.
How much is enough
The useful measure is contrast, not quantity. A reading chair needs its pool of light, but the pool only reads as a place if the floor around it is a little darker. Three to one is often enough; ten to one starts to feel theatrical.
A room lit everywhere is a room lit nowhere.
Leaving a room unfinished in this way takes some nerve, especially on a drawing, where dark areas look like mistakes. Mock-ups help: nothing persuades a client like standing in the half-light and feeling the room settle.