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Thoughts about Light and Sleep Abstract. Many aspects of health and disease are mainly determined by the constant change between light and darkness during a solar day. The resulting physiological rhythms correspond to the circadian rhythm, which was one of the most central drivers in the evolution of humans. However, over the last 20-30 years, these natural rhythms of the change of light and darkness are being increasingly ignored by modern societies. It is well known that these rhythms are modulators of many physiological pathways and any desynchronization or misalignment will activate different pathophysiological pathways, which contribute to the risk of chronic diseases. Light pollution by widespread illumination of our environment and the night sky and uncontrolled man-made use of any light source plays a key role in the pathogenesis of sleep disturbances. Blue light exposure in the evening from any artificial light source (especially from electronic device screens) is of special relevance in this context. In this article a few key facts concerning light, sleep and diseases are presented. We should by all means account for the effects of light and darkness and stop any further light pollution.

Everything in nature and life is occurring in a rhythmic manner. The major “Zeitgeber” is the change of light and dark during a 24 h day. This circadian rhythm is besides others reflected in circadian rhythms of behaviors or different biochemical parameters. A disruption of the circadian rhythm has a high pathophysiological potential. In this article a few basic issues about the role of circadian rhythms and the pathophysiological importance of desynchronisation are reviewed.