This study investigated the non-image forming (NIF) effects of dynamic light on alertness, cognitive performance and mood on mental fatigue, as well as moderation of task difficulty in lighting perception. Sixteen participants completed a psychomotor vigilance test (PVT) and two complex cognitive tasks (multi-attribute task battery-II (MATB-II) and n-back) with low, medium and high difficulty levels under dynamic (4000 to 12 000 K, melanopic equivalent daylight illuminance (EDI) = 224 lx to 420 lx) and static (4000 K, melanopic EDI = 224 lx) lighting with illuminance set at 500 lx on the desk. Psychological, behavioural, biochemical and electrophysiological responses to light were assessed. The results showed that exposure to dynamic light had significant benefits on subjective sleepiness, positive mood and task performance, which may be moderated by task difficulty. The intervention effect of dynamic light on fatigue was also found during an electrophysiological activity due to increase in the amount of attentional resources allocated to the tasks by dynamic light, but was not observed in biochemical measures.

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