Light pollution: street lighting gets the inner clock out of rhythm

Light pollution: street lighting gets the inner clock out of rhythm

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Artificial light suppresses the hormone melatonin

Humans lived in harmony with the natural day-night rhythm for thousands of years. At least since the discovery of the circadian rhythm it has been clear: cells also have a kind of internal clock and adapt their metabolism to the time of day. Artificial light from urban night lighting can disrupt this rhythm in humans and animals, as a current German research project shows.

Researchers at the Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB) found that even low light intensities, which predominate around the clock in cities, for example, have an impact on melatonin levels in humans and animals. Melatonin is again a hormone that clocks the internal clock. The study was recently presented in the journal "Sustainability".

What does melatonin do?

According to the research team, the hormone melatonin shapes the day-night rhythm in humans and vertebrates. Almost every cell in the body sets the internal clock depending on the concentration of this hormone. This influences, for example, processes of growth and reproduction.

Dependence on light and melatonin

The formation of melatonin is controlled by light receptors, which are located on the retina in the eye, for example. The more light hits the retina, the more melatonin is suppressed and the darker it is, the more melatonin is formed.

Street lighting suppresses melatonin production

The IGB team evaluated international data on the effects of light pollution on melatonin formation in humans and vertebrates. It was shown that the light from street lighting is already sufficient to slow down melatonin production. The sensitivity threshold in humans is six lux. A street lamp usually shines brighter.

Strong deviation from nature

According to the researchers, natural illuminance levels that living things experience reach just 0.001 lux on a starry night. On a full moon night, the illuminance level reaches a maximum of 0.3 lux. The light bell that emits a city already reaches an illuminance level of 0 1 lux. In the direct vicinity of street lighting, light intensities of more than 150 lux can be achieved.

Bells of light around cities

"The astonishing thing is that the very low intensities of a city's light bell are enough to suppress the production of melatonin in certain vertebrate classes such as fish and rodents," explains student author Dr. Maja Grubisic. Large areas worldwide are affected by this type of light pollution. This is shown by the evaluation of satellite data. The light from artificial lighting shines in the sky and is reflected by clouds and air particles, which creates a large light bell around the cities.

Episodes unknown

Little is known about the consequences of this connection. "So far there have been no studies on the effects of light pollution on melatonin formation," adds Dr. Franz Hölker from the study team. In particular, the consequences on human health are not yet sufficiently understood. (vb)

Author and source information

This text corresponds to the specifications of the medical literature, medical guidelines and current studies and has been checked by medical doctors.

Graduate editor (FH) Volker Blasek


  • Grubisic, M .; Haim, A .; Bhusal, P .; Dominoni, D.M .; Gabriel, K.M.A .; Jechow, A .; Kupprat, F .; Lerner, A .; Marchant, P .; Riley, W .; Stebelova, K .; van Grunsven, R.H.A .; Zeman, M .; Zubidat, A.E .; Hölker, F. Light Pollution, Circadian Photoreception, and Melatonin in Vertebrates. Sustainability 2019,
  • Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB): Light pollution suppresses "dark hormone" melatonin in humans and animals (accessed: December 18, 2019),

Video: The Dark Side of Street Lighting Light Pollution u0026 Pollination with Callum Macgregor (June 2022).


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