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Research confirmation: Night and indoor workers do not get enough light

People working indoors should be particularly aware about getting enough light for the sake of their mental health. This has been shown by researchers from Aarhus University and Aarhus University Hospital in the largest international study of light exposure in a worker population ever carried out.

Many people likely recognise the experience of not having seen any daylight after a working day that has only taken place indoors. And clearly this is also the case for anyone who works at night. How big a difference there actually is between being outside or inside – in terms of getting enough light exposure – has now been identified in a study carried out by researchers from Aarhus University.

The results are based on a study with five hundred test subjects including both daytime and night workers, who have carried light sensors  and kept a diary of their movements during a one-week period.

“The results emphasise that there is a big difference in the level of light exposure depending on whether someone is outside or inside during their working day. If people are unaware of this or aren’t working outdoors as a gardener or similar, then they will generally experience too little light in their everyday life. This can be problematic, because light is  important for our mental well-being," says Professor Henrik Kolstad from Occupational Medicine, which is part of the Department of Clinical Medicine at Aarhus University and Aarhus University Hospital.

Together with his research group, he has published the article Light Exposure during days with Night, Outdoor, and Indoor Work in the scientific journal Annals of Work Exposures and Health.

Lightening the mood

The amount of light or illuminance is measured in lux, where 100 lux corresponds to a very dark and overcast day, while 10,000 lux is full daylight. The study shows that indoor workers only receive 1,000 lux during daytime working hours in the summer and 400 lux during the winter. In comparison, outdoor workers receive an average of 4-5,000 lux in the summer and 1000-2,000 lux in the winter. This corresponds to the amount of light used in the treatment of depression. 

The purpose of the study was to gain an overview of how much or how little daylight we receive during the day, depending on what we are doing. This knowledge is important because daylight is important for our mental well-being and health, and it is something that everyone should take responsibility for. 

"This is something that developers and architects should know and take into consideration when building new housing or designing workplaces," says Henrik Kolstad.

Good news for people who work night shifts

The survey of night workers exposure to light is also part of the study. The focal point here has been the hormone melatonin which regulates the circadian rhythm and induces sleepiness. The production of melatonin is inhibited by light and the lack of melatonin has been associated with the occurrence of cancer in night workers. The new study shows that the majority of night workers are only briefly exposed to light levels which affect melatonin. According to Henrik Kolstad, this is reassuring news for the many people who work at night.

Background for the research study:


Professor Henrik Kolstad
Occupational Medicine, Department of Clinical Medicine, Aarhus University and Aarhus University Hospital.
Mobile: (+45) 2961 0359
Email: kolstad@clin.au.dk