The reflectance of the walls and floor is a determining factor in calculating the ambient light level in a space by the zonal cavity method. One way to increase the light level without spending additional energy on lighting is to paint the walls a lighter color or to resurface the floor in a lighter motif. The same can be accomplished by keeping the floor clean and waxed and the walls clean and in good repair.
Careful attention to other items in a space can further enhance the lighting environment. Keeping the windows clean allows maximum use of available daylighting, while clean sills and Venetian blinds reflect more daylight deep into a large space to supplement artificial lights. It’s also important to keep the lamps, lenses, and reflective surfaces on luminaires clean and dust-free.
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Excerpt from Energy Conservation Projects.