Electric lighting is a major component of electrical energy use in large commercial buildings and has additional significant impact on the cooling energy requirements. This paper evaluates the monitored performance of such an integrated lighting scheme in a recently completed 600,000-ft² office structure located in the San Francisco Bay Area. Decentralized data acquisition systems monitored 62 different locations in the building between May 1985 and January 1986, recording average illuminance levels and corresponding ambient lighting power usage across the north and south building sections. A graphic summary of data compares the performance of effectiveness of the buildings lightshelf system for north and south orientations. One counterintuitive conclusion of the study is that the dimmer north side light shelf scheme exhibits a higher potential (69% reduction from full power) for electric light reduction than the brighter south side scheme (56% reduction).