Lighting quality and energy-efficiency effects on task performance, mood, health, satisfaction, and comfort

The adoption of energy efficiency measures in building codes places constraints on lighting designers that they fear will reduce the quality of the lit environment. This experiment was designed to test the hypothesis that lighting quality, as understood by lighting designers, affects the task performance, mood, comfort, health, and aesthetic judgments of office workers. Nine lighting systems were installed in a windowless, 83 m(2) (880 ft2), open-plan office space containing six workstations. The designs combined three levels of lighting power density (LPD) and three levels of designers' lighting quality (DLQ) (recessed troffers with prismatic lenses; recessed troffers with parabolic louvers; indirect or direct/indirect fixtures). In the low LPD options, the ambient lighting systems were supplemented with task lighting. Temporary office workers (292 in total) each worked for one day under one of the nine lighting conditions. In addition to morning and afternoon visual performance tests, they performed a variety of computer-based and paper-based tasks designed to be representative of modern office work, and completed questionnaires to assess satisfaction and impressions of lighting quality, mood, physical comfort, and social behaviors. The results show that energy-efficient lighting and good-quality lighting can be compatible. For computer-based work under existing lighting power density limits, parabolic-louvered luminaires provide better verbal-intellectual and clerical task performance than recessed lensed luminaires. Verbal-intellectual task performance and visual performance were better under electronic ballasts than magnetic ballasts, regardless of lighting system.