This study examines the way people choose to use individual control of lighting, the effect of having such control on the illuminance selected for different activities and the performance of those activities and how people feel about having such control. The experiment took place in three small, windowless, private offices, one lit to a maximum of 1240 lx, another to a maximum of 680 lx, both these offices having a handheld dimming system. The third office was lit to a fixed illuminance of 490 lx. Eighteen subjects worked for one eight-hour day in each of the offices. During the day they carried out an alphanumeric verification task in forms which were visually difficult and visually easy, on paper and on a computer, as well as doing some casual reading. The subjects in the offices equipped with individual lighting control could use the control whenever they liked. The data collected showed that the subjects did use the individual lighting control to adjust the illuminance for different tasks, but there were wide differences between individuals. Use of the lighting controls saved energy. The ability to dim the lighting was considered highly desirable and made the tasks seem less difficult. However, the ability to control the lighting did not put the subjects in a more positive mood, did not make them more alert, and did not affect the performance on the task.
