It would seem that, if the luminaires are cleaned and relamped occasionally, the major light loss factors will have been taken care of. However, since high room surface reflectances have been shown to be a requirement for good system efficiency, any decrease in room surface reflectances will also increase light loss. Depending on the environment, room surfaces should be washed periodically and painted when the reflectance has dropped significantly. In the cleanest environments, room surface depreciation can easily account for a five percent decline in illuminance level in the space during a 24 month cleaning cycle. Bleaching out of paint, curtains, or other materials, as well as light-colored dust, can cause the appreciation of surface reflectances.
Most preliminary design assumes that the space is entirely empty.
When furniture and equipment are placed in a room, the distribution of the light can change radically. Furniture that is light in color with a matte finish will help prevent glare and absorption of light. Shadows that occur from equipment shielding light can be prevented by properly locating equipment with respect to the lighting system.