The effect of light directionality on creative performance and subjective sleepiness in the early afternoon

The appropriate lighting conditions support concentration, cognitive performance and overall well-being. While this is especially true for daylight, many meeting rooms and co-working areas are in windowless, core areas of the buildings, making carefully designed artificial lighting even more critical. The spatial distribution of light has been documented to affect alertness and cognitive performance in simple tasks. However, its effect on more complex, creative challenges is largely unresearched. In this study, two distinct lighting conditions were tested in a simulated meeting room. The conditions represented either upper- or side-dominant lighting with a constant irradiance of 305 lx melanopic EDI at the eye level of participants. In a within-subject design, 35 participants completed a 2-h protocol involving tasks assessing various aspects of creative thinking (divergent, convergent and mental rotation), subjective sleepiness, room appraisal and mood. Results showed that side lighting significantly improved performance on the divergent creativity task but also led to increased subjective sleepiness over time. Conversely, upper lighting maintained stable sleepiness levels throughout the protocol. No significant effects were found for other dependent variables. Additionally, covariate analysis revealed a significant correlation between increased performance in creative tasks and extended time spent under daylight (indoors) prior to the experiment.