Reflectance indicates the percentage of luminous flux reflected by a surface. The reflectance of light surfaces is high; that of dark surfaces is low. White walls reflect up to 85% of the light that strikes them, while light-coloured wood panelling reflects as much as 35%. The reflectance of red brick, however, is only 15%.

So the darker the decor and furnishings, the more light is needed to produce the same illuminance at the working plane.

Specular materials with directional reflection characteristics can also be defined by their reflectance. The reflectance of highly polished anodised aluminium, for example, is 85%.