Visual Comfort and Acute Alerting Effects of Diurnal Intermittent Bright Light

Intermittent bright light during the night has shown to be able to generate circadian phase-shifting effects, suppress melatonin and induce alertness, but little attention has been devoted to the effects of diurnal intermittent bright light. Following a night of sleep restriction, forty participants were exposed in a counterbalanced within-subject design to an intermittent (100 lux–1000 lux), a continuous dim (100 lux) and a continuous bright light condition (1000 lux) each lasting 90 min. Repeated assessments of self-reported sleepiness, cognitive performance and physiological arousal as well as subjective visual comfort were taken during each light condition. Results showed that alertness-related parameters were not significantly affected by the light conditions: neither the intermittent nor the bright condition improved alertness compared to the dim condition. Visual comfort was highest in the dim condition, followed by the intermittent and bright conditions respectively, even though the visualizations showed marked decreases in visual comfort during the bright light phases in the intermittent condition. The results illustrate the diversity in mechanisms underlying these visual experiences and neurobehavioral responses.