Light quality is important to energy efficiency because rooms with better lighting quality need less watts of illumination. Light quality describes how well people in a lighted room can see to perform visual tasks, like cooking or reading. Good lighting quality is characterized by uniform brightness and the absence of glare.
Imagine, for example, direct intense sunlight streaming through windows of a room with chocolate brown carpets and dark wall paneling. Bare light bulbs light the room’s dark areas. You will have difficulty seeing or working well in this room, and your eyes will be adjusting constantly as they wander over dark and bright areas. To reduce the contrast and improve the visual comfort of this room with more electric lighting would require a very high level of illumination, using many watts of electricity.
Now consider a room bathed in soft light. You can hardly tell where the light is coming from because no area of the room appears much brighter than another. Window shades diffuse the natural light as it enters. The walls, ceiling, floor, and work surfaces are light colored. The electric lights have diffusers that distribute light around the room. Light bounces off the light-colored surfaces without creating glare.
People can perform tasks faster and with fewer mistakes in this high-quality lighting environment. Lighting such a room requires far less electric lighting than the first example because of its superior lighting quality.
Keep this idea of lighting quality in mind when you are painting and decorating. A common error people make is selecting a paint that is too dark, resulting in a room with poor lighting quality. Stay with white for ceilings and the lightest tints of your chosen color family for walls. If you must use a darker color, reserve it for the window trim and baseboard. Both your eyes and your electric bills will benefit.
For more information on lighting, see Residential Energy: Cost Savings and Comfort for Existing Buildings Chapter 7.