The effects of ambient light on task switching depend on the chronotype.

The aim of the present study was to investigate the synchrony effect between chronotype and time of day on task switching and vigilance, and the effect of high illuminance on the performance of two chronotypes at their non-optimal time. Four 46 minute sessions were administrated on separate days, the illuminance (200 vs. 1200 lx at eye level) and time of day (1.5 hours vs. 10.5 hours after waking up) were manipulated within participants. We found that high illuminance (1200 lx) significantly decreased the latency switch cost only for evening type independent of time of day, and there was a trend that low illuminance (200 lx) was better for morning type to decrease latency switch cost compared with evening type. The high illuminance could decrease the subjective sleepiness significantly for both chronotypes at the later part of the experiment. No synchrony effect on task switching and vigilance was found in the present study. The results suggested that the effect of ambient light on task switching was modulated by chronotype. Current study enriched the research on the effect of ambient light on task switching. When setting the optimal light environment, we should considerate the individual difference such as chronotype. [ABSTRACT FROM AUTHOR]