The effects of lighting levels on the perception, performance and physiological responses in offices

It is widely acknowledged that light plays an important role in individuals’ perception and cognitive functions. However, the optimal daytime lighting levels that benefit office workers’ experience, performance, and physiology remain to be fully elucidated, as most studies to date have evaluated only two to three lighting conditions at low and high illuminance levels. This study employed a within-subjects design with six lighting conditions based on melanopic equivalent daylight illuminance (melanopic EDI) set at equal logarithmic intervals, with melanopic EDI values of 54 lx, 90 lx, 150 lx, 250 lx, 417 lx, and 694 lx at eye level. Thirty healthy participants were exposed to each lighting condition for 75 min, and their feedback, task performance, and physiological parameters were collected. Results indicated that the most comfortable and satisfactory lighting condition was the melanopic EDI of 150 lx, while no statistically significant differences were found in subjective alertness and mood. The effects of lighting on cognitive performance was related to the task type. Scores of memory and problem-solving tasks all increased with melanopic EDI set at 250 lx, while performance on other tasks did not improve significantly across lighting levels. Additionally, no statistically significant differences were found in physiological measures such as heart rate and skin temperature. By experimentally exploring multiple lighting conditions, this study provides insights into the quantitative specification of lighting levels for visual and nonvisual needs. The findings suggest a divergence, with a melanopic EDI of 150 lx facilitating comfort and satisfaction, while 250 lx enhancing cognitive performance. Notably, higher lighting levels did not always lead to better outcomes, with the highest level (melanopic EDI = 694 lx) even reducing comfort and satisfaction.