Background Shiftworkers’ increased risk of adverse health outcomes has been linked to their exposure to light-at-night (LAN). However, few data characterising light exposures in nighttime working environments have been reported. The purpose of this study was to measure and compare shiftworkers’ exposures to LAN in the province of British Columbia, Canada.

Methods Between October 2015 and March 2016, over 150 personal full-shift data were collected from more than 100 shiftworkers in emergency health services (paramedics, dispatchers) and healthcare (nurses, support aides, security, pharmacy, laboratory staff). Participants wore a small continuous monitoring device to measure LAN exposure once per minute. Preliminary analyses during the 23:00–05:00 period were conducted to characterise exposure levels with potential impacts on melatonin secretion and alertness.

Results Personal light exposure levels ranged from <5 lux (minimum) to >650 lux (maximum). Cumulative time ≥1 hour above 30 lux (minimum level influencing melatonin secretion) occurred in over 60% of samples, and in over 40% of samples using a 100 lux cut point (midpoint of light’s maximum alerting effect). Significant exposure differences were seen across occupations and workplaces. Nurses, aides, and laboratory workers had the longest cumulative time exceeding 100 lux; dispatchers had the longest cumulative time below 30 lux. By workplace, laboratory, intensive care, and labour and delivery workers had the longest cumulative time exceeding 100 lux; call centre workers had the longest cumulative time below 30 lux. Within-worker variation across shifts was most pronounced among laboratory assistants and least pronounced among dispatch officers.

Conclusions This study constitutes an initial step in documenting and comparing levels of LAN exposure across shiftwork occupations, workplaces, and time. Results will be useful for planning future LAN sampling strategies, assigning exposure estimates in epidemiological analyses, and identifying groups of shiftworkers at greatest risk of circadian disruption and/or fatigue at work.