A field study of illuminance reduction

Many offices are illuminated at levels much higher than necessary for office tasks. Lowering ambient illuminance, while maintaining task illuminance, i.e., task-ambient lighting, can save energy without impairing visual performance. A downside of task-ambient lighting is rooms appear dark and gloomy. Maintaining brightness perception is the key to success in task-ambient lighting. To examine the practicality of brightness-enhanced task-ambient lighting for illuminance reduction a field study was conducted in a modern office setting. This study examined office workers' responses to approximately one-third lower ambient illuminance than the initial illuminance and two measures designed to enhance brightness perception: higher correlated color temperature lamps (6500 K) and sparkle elements. Surveys showed that after an initial adaptation period, office workers were generally satisfied with the lower level of ambient lighting. They did increase their use of task lighting at their desks but this had little impact on overall energy consumption. The 6500 K lamp was effective at increasing perceptions of brightness in offices with the lower ambient light level. Over a longer period, the sparkle elements used did not significantly change workers' perceptions of gloom. (C) 2005 Elsevier B.V. All rights reserved.