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Non-visual effectiveness of light at night as a function of the light direction

Project number: F 2496 Institution: Federal Institute for Occupational Safety and Health (BAuA) / Technische Universität Berlin Status: Ongoing Project Planned end: 2022-12-31


Light not only enables visual perception. About two decades ago, a new type of photoreceptor in the retina was detected that gives rise to the so-called non-visual effects of light. Via these photoreceptors light coordinates numerous processes in the human body with the rhythm of day and night and influences both physiological processes (like the release of hormones) and the cognitive abilities of humans (e.g. alertness).

During the night shift, light is required in the workplace in order to perform the work tasks. A higher light intensity increases the alertness and thereby also the safety. At the same time, light at night suppresses the release of the sleep hormone melatonin. According to the current state of knowledge, permanent suppression of melatonin by light at night probably plays an important role in the development of chronic diseases.

The non-visual light effect is dependent on the intensity and spectral composition of light, but also on the direction of light entering the eye, since the photoreceptors responsible for this effect are not evenly distributed over the retina. Light that strikes the eye from above and hits the bottom half of the retina, for example, suppresses the night-time release of melatonin stronger than light from below. In laboratory tests with subjects at night, a dependency of alertness on the direction of light entering the eye was found as well.

Since the direction of light at night causes melatonin suppression and affects alertness, this subject study investigates if by appropriate positioning of light sources during night work it is possible to reach a high level of alertness and sufficient visual stimulation for fulfilling the visual task, while at the same time reducing melatonin suppression. This would enable health-promoting lighting recommendations for workers in control centers, control rooms or similar workplaces.


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