• Project number: F 2449
• Institution: Federal Institute for Occupational Safety and Health (BAuA)
• Status: Completed Project

Description:

Light is the most important synchroniser (or Zeitgeber) for circadian processes in the human body with the Earth’s 24-hour day-night rhythm. Too great an exposure to light at night as well as not enough light during the day, for example when working night shifts or when working predominantly indoors with little access to daylight, can lead to circadian rhythm disruption which in turn is associated with health impairments.

Within the project, the circadian light exposure of 160 employees in various occupations was investigated between winter 2020 and spring 2023. Employees working night shifts (two occupations), employees working indoors during the day (eleven occupations) and employees working outdoors, where sufficient daylight exposure can be assumed (four occupations) have been included in the study. The test subjects measured their exposure to light over the course of one working week during and beyond working hours, in winter and in spring/summer.

The circadian light exposure was quantified as Melanopic Equivalent Daylight Illuminance (MEDI). MEDI describes the amount of daylight required for a comparable stimulation of the corresponding photoreceptors in the eye. Taking into account the new recommendations for indoor MEDI levels, the exposure time within certain MEDI ranges was analysed for the professions and seasons studied. With regard to the scientific recommendation for a minimum MEDI value of 250 lx indoors during the day, it can be stated that MEDI values are higher than 250 lx for several hours in spring/summer for both night shift workers and daytime indoor workers. While a 250 lx MEDI value is hardly ever reached by night-shift workers in winter, it is usually higher than 250 lx for 1.5 to 2 hours for daytime indoor workers.

Furthermore, the circadian light exposure was analysed as a 24-hour melanopic equivalent daylight dose, i.e. the product of the MEDI value and the exposure time. The percentage of the dose in relation to the respective dose of gardeners was also calculated. The dose for night shift workers is less than 10 % in winter and around 20 % in spring/summer, relative to the respective dose for gardeners. The corresponding values for daytime indoor workers are on average 19 % in winter and 23 % in spring/summer. Thus, the melanopic equivalent daylight dose for night-shift workers and daytime indoor workers is significantly lower than for outdoor workers. Finally, three-dimensional job exposure matrices were created including the melanopic equivalent daylight dose, the seasonal dependence and the occupations investigated.

As a tool for occupational health research, a job exposure matrix can help to estimate dose-response relationships and exposure-related health risks, even if no direct exposure data are available for an epidemiological study.