Aim: As our understanding of light's impact on human health grows, studies examining light exposure and related health outcomes in everyday settings are increasingly important, particularly in high-risk groups like nightshift workers.

Methods: In this observational study, we monitored personal light exposure and physiological functions in a large cohort of healthcare nightshift workers using a spectrally resolved light dosimeter and wearable body temperature, actigraphy, and electrocardiography sensors.

Results: Our findings revealed a common occurrence of unfavorable light conditions during both shift types. During nightshift work, participants frequently experienced exposure to biologically potent cool-white LED lighting. On dayshifts, melanopic light levels often failed to meet recommended guidelines, with daylight as the primary source of bright light levels. Sleep duration, but not quality, significantly varied between shifts, with longer sleep before the first nightshift but shorter sleep on subsequent nights. Daytime and nighttime napping helped compensate for reduced sleep on nightshifts. Limited associations between light exposure and sleep were found, partially contradicting existing knowledge. Diurnal physiological and activity rhythms followed the change from day-active to night-active schedules; however, the change in physiological rhythms appeared partly dissociated from that of activity, suggesting a circadian modulation. Moreover, physiological functions exhibited bi-directional phase-shifts across consecutive nightshifts, which may have been mediated by differences in daytime light exposure before the first nightshift.

Conclusion: By employing a multi-wearable approach including recent sensors, we provide new insights into the lighting environments experienced by nightshift workers and the potential impact of nightshift work and light exposure on endogenous circadian rhythms.