The dark side of too much light

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When they look up at the night sky, many people in German cities wonder what has happened to the stars. The constant presence of artificial light in big cities turns night into day and reduces the radiance of the stars. We like to illuminate our environment intensively because light and brightness give us a reassuring sense of security. In addition, artificial light symbolises prosperity and modern life. Despite its countless advantages, however, it also has a dark side: light pollution is on the rise – and its effects on human beings and nature are as yet unknown. The term “light pollution” means that the stars in the night sky can no longer be seen clearly as a result of the many artificial light sources.

“Loss of the Night” research platform

too much artificial light can harm nature and the environment.

The biologist Dr Franz Hölker from the Leibniz Institute of Freshwater Ecology and Inland Fisheries in Berlin coordinates the “Loss of the Night” research platform, where biologists, physicists, lighting engineers, town planners and humanities scholars are jointly exploring the consequences of the “pollution of natural light” and the “loss of the night” for human beings and nature.

How light pollution disrupts biological rhythms

“We are only just beginning to understand the precise effects of artificial light at night”, says Hölker. However, laboratory studies have already shown that even one lux – a low level of illumination roughly equivalent to that emitted by a candle at a distance of one metre – affects hormonal production in fish. Consequently, fish at night produce less melatonin, the hormone that is used to control the circadian rhythm in humans, too. In many organisms, reproductive and hunting behaviour are also based on this inner clock. Bright light at the wrong time can disrupt these biological control rhythms. In addition, artificial light at night affects biodiversity. Biologists in the research network are therefore investigating which insects are attracted by which types of street lamps and may consequently be absent from waterways and other places, for example as a source of food to fish.

New lighting concepts to protect humans and nature

“We will only be able to draw up scientifically founded lighting guidelines once we have properly understood the consequences for natural systems, human beings, our sleep and the way we coexist. And such guidelines are essential if light is to be used in a responsible and sustainable manner”, explains Hölker. Not only do sustainable lighting concepts protect humans and nature; they also satisfy our need for security at night – for example on the roads or in public places.

App-based citizen science

The researchers have developed an app – which can be used by anyone wishing to help precisely describe the degree of “sky glow” around the world. It measures the brightness of the sky and the visibility of the stars at any site and can be downloaded free of charge in 15 different language versions. The measured data are sent to the international Globe at Night and Myskyatnight citizen science projects , where global light pollution maps are drawn up to help scientists and amateur enthusiasts alike to “shed light” on the correlations between light pollution and health, biodiversity, quality of life and many other factors.