Non-image forming effects of illuminance and correlated color temperature of office light on alertness, mood, and performance across cognitive domains

Research has explored acute effects of light level and correlated color temperature (CCT) of indoor lighting on subjective measures of alertness and task performance during daytime. Yet, these investigations did not render a conclusive or consistent finding on the relative contribution of illuminance and CCT on various cognitive domains. The current study (N = 57) investigated diurnal effects of illuminance level (100 lx vs. 1000 lx at eye level) and correlated color temperature (3000 K vs. 6500 K) in a simulated office environment on subjective alertness and performance in sustained attention, response inhibition, conflict monitoring, and working memory. Moreover, effects on mood and appraisals were explored. The findings revealed that the high vs. low CCT manipulation elicited no statistically significant benefits on subjective alertness and task performance, but revealed an increase in negative affect. Exposure to high vs. low illuminance rendered subtle benefits on participants' mood and selectively improved performance. Reaction speed in the Go/No-go task and Flanker task (only incongruent trials) were significantly enhanced with 1000 lx compared to 100 lx lighting, but not statistically significant in the PVT task or the PVSAT task. Effects are discussed in consideration of task type and melanopic activation under the various light conditions.