Most buildings and facilities, by necessity, have cleanup crews come in after the close of business. The entire space is brightly lit for several hours every evening while these crews do their work. This expense can be avoided entirely if the crews come before darkness or if they do their job discreetly during the daytime. Alternately, the janitorial services can be instructed to use the minimum lighting necessary and to turn off the lights in areas not in use.
A more sophisticated approach is to install a lighting controls system for the entire building that turns a block of lights on and off at set intervals throughout the night, with sufficient time allowed in each block for the cleanup crews. A little more economical system is to install occupancy sensors, turning off lights when there is no noise or movement in an area for 10 or 15 minutes.
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Excerpt from Energy Conservation Projects.