A week in the life of full-time office workers: Work day and weekend light exposure in summer and winter

• Measured 24-h light exposure in full-time office workers in summer & winter weeks.
• Consistent workday/weekend schedules and circadian phase between summer & winter.
• Morning light exposure was greater on workdays versus weekends in both seasons.
• Early evening light exposure was greater in summer versus winter on all days.
• In the 2 h before sleep onset, light exposure was consistently low (<20 lux).

Little is known about the light exposure in full-time office workers, who spend much of their workdays indoors. We examined the 24-h light exposure patterns of 14 full-time office workers during a week in summer, and assessed their dim light melatonin onset (DLMO, a marker of circadian timing) at the end of the working week. Six workers repeated the study in winter. Season had little impact on the workers' schedules, as the timing of sleep, commute, and work did not vary by more than 30 min in the summer and winter. In both seasons, workers received significantly more morning light on workdays than weekends, due to earlier wake times and the morning commute. Evening light in the two hours before bedtime was consistently dim. The timing of the DLMO did not vary between season, and by the end of the working week, the workers slept at a normal circadian phase.