Effect of Wall Brightness on Room Illumination

By S. De Backer, M.P. Diebold, M.P. Milone

While there is an intuitive connection between wall brightness and the electrical demand for illuminating a room, there has been little data reported to quantify this relationship. Here, we report the relative electrical load needed to light a room at the 500 lux level specified by European lighting standard EN12464-1:2011, as a function of wall brightness.

A room was painted white, black, and two intermediate shades of gray, and room brightness was measured at multiple locations and directions using four light levels (controlled with a light dimmer), for both warm and cool fluorescent bulbs. Results were compared to computer modeling. Based on these results, we determined the expected electrical requirements for rooms painted with over a dozen “colors of the year,” as designated by major décor coatings manufacturers.

The results were compared to the electrical requirement for a white wall. Significant energy savings are possible when painting a dark wall white.