Energy-Efficient Lighting Options: Predicted Savings and Occupant Impressions of Lighting Quality

Detailed simulations of lighting and HVAC energy consumption were performed on a prototype office building in six North American climates. The goal of these simulations was to calculate the overall energy savings attributable to reductions in lighting power density (LPD) from 25.8 W/mP2P (past practice) to 17.2 W/mP2P (current code) to 8.6 W/mP2P (low). Results showed that as LPD decreases, reductions in cooling energy, due to reductions in heat produced by lighting, could substantially increase cost savings over the cost savings attributable to lighting in isolation, particularly in warm climates. Further, nine different lighting designs were installed in a windowless, 83 mP2P (880 ftP2P), mock-up open-plan office space, containing six workstations. The nine lighting designs resulted from a combination of the three LPDs used in the simulations, created using three ambient lighting technologies (recessed troffers with prismatic lenses; recessed troffers with parabolic louvers; indirect or direct/indirect fixtures); in the low lighting power density options, the ambient lighting systems were supplemented with task lighting. At least thirty participants, in groups of three to six, worked for a full day under one design (292 participants in total). 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. Ratings of environmental satisfaction, lighting quality, task difficulty, and self-reported productivity indicated that participants preferred parabolic louver fixtures over prismatic lens fixtures, and preferred the low energy lighting designs.