Light of both high and low melanopic illuminance improves alertness and attention during daytime

Light exposure during the day exerts acute effects on attention, such as how alert and ready a person is for solving problems and goal-oriented behavior. However, to increase the understanding of how different light conditions during daytime affect our attention, there is a need for more studies. The current study, using a sample of healthy, young adults (N = 39; 21.7 ± 2.6 y, 61.5% female), tested the acute effects of morning exposure (09:00-11:00) to four artificial lights on attention and alertness with the Psychomotor Vigilance Task (PVT). The PVT was administered three times in short-wavelength "blue" light [SWL, high melanopic illuminance], long-wavelength "red" light [LWL, low melanopic illuminance], and bright white light [BWL] of high correlated color temperature, and white dim light [DL] as control condition. PVT measures included fluctuations in attention, quantified as intra-individual Reaction Time (RT) variability and the number of lapses; mean RT; and optimum response capability (10% fastest RTs). Compared to DL, participants had significantly fewer lapses and faster mean RT during SWL and LWL, and they enhanced their optimum responses in LWL. There were no significant effects of BWL, and light did not affect RT variability. Surprisingly, SWL was not superior to LWL. Hence, our results suggest that light of both high and low melanopic illuminance can improve alertness and attention in the morning.