The Effect of power constraints on occupant lighting choices and satisfaction: a pilot study

Several recent studies have provided evidence that individual lighting control results in occupant satisfaction benefits. As part of a larger series of pilot studies, we examined the use of individual controls under various lighting power constraints. The studies took place in a mock-up open-plan office space, in which participants spent around two hours doing typical office tasks and answering satisfaction questionnaires. Participants were offered control over lighting circuits via virtual dimmers on their computer screen. The effect of power constraint varied depending on how the constraint was applied. When the constraint was obvious to the participant there were negative satisfaction effects, but when the constraint was hidden there were no apparent satisfaction penalties. One of the hidden constraints we applied was similar to a load shedding situation, whereby lighting is slowly dimmed to avoid peak load problems. We reduced light level slowly (1% of maximum output every 2 minutes) after participants had made their initial lighting level choices. Participants were not conscious of the dimming, allowing the illuminance to fall by 40-50% (typically) before choosing to increase light levels. Therefore, as a method of avoiding peak load-induced power outages this method has promise. These pilot study findings have important implications for practice, and warrant a larger future study.