Preferred surface illuminances and the benefits of individual lighting control: a pilot study

Current office lighting recommendations stress the importance of vertical surface illumination over horizontal desktop illumination for VDT work, where the occupant is primarily in a “heads up” position. We investigated this recommendation by creating two very different lighting conditions in two workstations in a mock-up open-plan office space. One workstation was provided with conventional, dimmable ceiling-recessed parabolic fixtures. The other, adjacent, workstation featured an innovative, dimmable, “partition washer” system designed to preferentially light the vertical surfaces in the occupant’s field of view; this was supplemented by a fixed 150 lx on the desktop from overhead. Participants (lighting experts) were assigned to one of the workstations and spent around 7 minutes reading and evaluating an on-screen article and a summary of the article, and completing an on-screen questionnaire on satisfaction with the lighting. This was done under one of four fixed initial lighting conditions. The participants then set the lighting to their own preference using on-screen dimmers, and repeated the task and questionnaire. Participants then switched workstations and repeated the procedure under the other lighting condition. Results showed that there was no significant difference in satisfaction between lighting conditions, although the partition washer condition required significantly less power. Participants were more satisfied with the lighting after control independent of lighting conditions, as expected. Further, derivation of preferred surface illuminances suggests that supplementary partition illuminance, beyond that which is provided by ceiling-recessed parabolics, is desirable.