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Lack of light and light at the wrong time

Circadian rhythm and occupational safety, from the 3/2017 edition of baua: Aktuell

Many physiological processes in the human body, such as the sleep-wake cycle, the release of hormones, changes in blood pressure or cognitive performance, are subject to the circadian rhythm. It is controlled by the central "internal clock", which is situated in a small area of the hypothalamus and which steers other "internal clocks" in the organs and cells of the body. The central "internal clock" adapts to the external 24-hour day-and-night rhythm with the support of external stimuli known as zeitgeber – with the keyword here being "synchronisation".


The most dominant zeitgeber is light. Information about the light conditions is recorded and relayed by non-visual photoreceptors in the retina of the eye. Therefore, both natural and artificial light do not simply serve the purpose of enabling eyesight. The non-visual effects of light on the circadian rhythm depend on several parameters, such as the intensity and the spectral composition of the light or the time of the light exposure. Blue light with a wavelength between approximately 450 nm and 490 nm, for example, has a stronger non-visual effect than light of other wavelengths.

The desynchronisation of the "inner clock" due to light at the wrong time during shift work or due to lack of light can promote impairments such as a lack of concentration, as well as metabolic disorders, cardiovascular diseases, the onset of depressive moods, or can even lead to an increased risk of cancer.

The effect of light on safety

The influence of circadian rhythms on fatigue, attention, cognitive performance and sleep is particularly evident. In this respect, such rhythms are relevant for the occupational safety and can also be seen to correlate with incidents and accidents. BAuA's analysis of some 3,000 industrial incidents, for example, demonstrated that daily and seasonal variations in the daylight were also reflected in the accidents, which suggests that their occurrence was influenced by the circadian rhythm.

The effect of light on health

The non-visual effects of light also play an essential role in terms of mental and physical health. In this context, the synchronisation of the circadian rhythm with the natural day-and-night rhythm is particularly important. In the scope of BAuA's research project on the "Effects of circadian desynchronisation", the effects of two disruptive mechanisms that can bring the internal clock out of sync were examined: the lack of light and light at the wrong time. In this respect, it was found that a lack of light during the day can lead to chronic fatigue, a reduced attention and later bedtimes. Furthermore, blue light in the evening resulted in poorer attention the next morning and a shorter duration of sleep. Since the knowledge about the actual levels of light exposure of specific occupational groups is still limited, in a joint project of BAuA and the Public Health England, the 24-hour personal light exposure of shift-working nurses is currently being examined. In a new BAuA longitudinal study on the social, psychological and physiological consequences of permanent night shifts and 12-hour shifts, the light exposure of these employees is being examined as well.

Chances and risks of biologically effective lighting

The effect of light on the circadian rhythm is currently undergoing intensive research. Despite many open questions in this area, the lighting industry is already developing so-called "biologically effective" lighting. In this context, the discussed effects are particularly relevant for occupational safety and health, and present both chances and risks to employees. In the future, it will be important to make use of the chances in practical applications, to minimise the risks, and to take both into account in the standardisation and in the further development of technical regulations.

In October 2016, BAuA held a European workshop on "Light, health and shift work" in Dortmund, Germany. A follow-up workshop entitled "Light and health at work" has been planned for 2018.

This article appeared in the 3/2017 issue of baua: Aktuell which can be downloaded on our German Website.