| Abstract | This paper reports on two experiments conducted in the same office laboratory. As part of a larger experiment, 58 participants worked for a day under one of two lighting designs. The first design used ceiling-recessed parabolic luminaires only; the second design employed the same parabolic ambient lighting, with the addition of an angle-arm task light. Participants had no control over the lighting until the afternoon, when they were offered dimming control over the ambient parabolic lighting; participants with task lighting were also permitted to move the arm location. During the day participants performed a variety of simulated office tasks, as well as completing a number of questionnaires on mood, satisfaction, and discomfort. There was no main effect of lighting design on questionnaire outcomes, however, task lighting was associated with performance improvements on some tasks. Interestingly, provision of a task light did not lower participants' preferred ambient light output. The second experiment, with 31 participants, followed up on this final point. Again, ambient lighting was provided by ceiling-recessed, parabolic luminaires, and participants were provided with a task light. For two task light types (angle-arm and luminous shade) at three different levels of output (0%, 50%, and 95%), participants used a dimmer to select their preferred level of ambient lighting. Increasing task lighting did reduce chosen ambient light output, but the reduction in lighting power was small, and only about the same as the power drawn by the task light. Results suggested that participants did not dim ambient lighting further because they preferred to maintain illumination on non-task surfaces, and to avoid extreme luminance ratios. |
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