Lighting Design Lab researcher Eric Strandberg did some computer simulations of a room and varied only the surface reflectance, while keeping the lighting the same.

Much of the light in interior spaces is reflected off of room surfaces at least once before reaching task areas. Every time light bounces it loses energy, so how reflective the surfaces are will impact your measured light levels.

Changing surfaces from low-reflectance (brick, wood, dark carpet) to high-reflectance (white or light paint, light floor coverings) increased the measured light by 50%. Why not more?

Doors, artwork and furniture take up about half a wall's potentially reflective surface. But that's not the only factor.

Another factor is the way the luminaires distribute light. A room with direct lighting (recessed cans or highbay industrial lights) will drive more light onto the floor, so ceiling reflectance will have less impact than floor reflectance. Conversely, if the lighting is predominantly indirect, a high ceiling reflectance is critical to achieving high light levels.

Lightening the surfaces also smoothes out the light in a room -- there is less difference between the light and dark areas of the room -- so we perceive the space to be lighter.

For his newsletter article, Strandberg modeled a typical room. He points out that in large spaces, like ballrooms or parking garages, the walls play a smaller part in reflecting light.