Objective Exposure to high levels of light during night and low levels during day time may have adverse health effects. Our aim is to characterise light exposure levels in night shift, outdoor, and indoor day workers.

Methods We recruited 535 night shift, outdoor, and indoor workers that for seven days wore a Phillips Actiwatch Spectrum on the upper dominant arm during days of work and days off. This device records red, green, blue and white light level every minute. Participants also filled in a diary on work and sleep hours that was synchronised with illuminance- calibrated white light exposure recordings (lux).

Results A total of 3.7 million one-minute lux recordings were obtained. They were highly right skewed with work day mean and medians of 968 and 33 lux, respectively. Night shift workers showed a night time mean level of 20 lux, which was fourfold the levels seen in indoor (6 lux) and outdoor workers (4 lux) during night time. However, 24 h mean levels during workdays were lower in these mainly rotating night shift workers (572 lux) than in outdoor (1449 lux) and indoor workers (996 lux). Indoor workers compensated for low work time exposure by higher off work illuminance levels, while this was not the case for the night and outdoor workers.

Discussion This study provides illuminance levels during work, leisure and sleep that may link laboratory and epidemiological findings. Account has to be taken that periods where the measuring devise was not used was excluded in the study.

Conclusion Night shift workers experience higher levels of illuminance during night shifts but lover overall levels during work days compared to indoor and outdoor workers. Both may affect circadian rhythm. Outdoor workers experience illuminance levels during the day that has shown to ease depression in experimental studies.