Light

Daylight in deep rooms

1 June 2026

Light reaches about twice the window head height into a room. Planning around that number saves a lot of lamps.

A room can have a large window and still feel dark at the back. Daylight falls off quickly with distance from the glass, and the height of the window head matters more than its width.

Useful daylight reaches roughly 2 to 2.5 times the height of the window head above the floor. A head at 2.4 m lights a room about 5-6 m deep.

Ways to push light further

1. Raise the window head to the ceiling instead of leaving a deep wall above it
2. Keep the ceiling and the back wall light in colour - reflectance does more than extra glass
3. Splay the reveals so the wall around the window is lit, not silhouetted
4. Add a second window on another wall; light from two sides evens out glare
5. Use a clerestory or a roof light for the deepest part of the plan

Wide, low windows give views but light only the front of the room. Tall, narrow windows spaced along a wall often light it better and leave more wall for furniture.