Source: Office for technology-assessment at the German Bundestag
Author: Christoph Schröter-Schlaack; Christoph Revermann; Nona Schulte-Römer,
Institution: Institute for technology assessment and system analysis(ITAS)
Field of Research: Environmental and health risks: light pollution
Source file: DOI:10.5445/IR/1000121964
re:look climate text: Nadine Oppenberg and Philipp Lengsfeld
re:look climate teaser:
In the previous reports the research report of the Office for Technology Assessment at the German Bundestag by C. Schröter-Schlaack, C. Revermann, and N. Schulte-Römer from 2020 on the subject of light pollution, the risks and acute impairments caused by light pollution were listed, as well as the countermeasures in Germany, in Europe and in non-European countries. This report deals with the environmental risks, caused by light pollution
The impairment of light pollution affects as well organisms that use the dark phases as rest periods as the crepuscular or nocturnals, which are specialized in the dark. Changes in the behavior of organisms caused by light pollution continue to have an impact on the entire ecosystem. The consequences of light pollution on the environment are far-reaching and are shown below using a few examples.
Effects on plants
Plants are very sensitive to light exposure. Long-wavelength red light, in particular, can change the perceived day length of plants, which can result in delayed leaf shed or postponed flowering. Temporal changes in these processes can result in damage to the plant tissue due to sudden frost. This delayed shedding of leaves near street lights could already be observed in the 1930s. Hölker et al. (2015) studied the effects of street lighting on microorganisms of aquatic origin. After a year of artificial lighting with a strength of 7 to 8 lx, the composition of the communities in summer and winter could no longer be distinguished from each other due to the disturbed day length. In further laboratory experiments, they showed that plants exposed to 70 lx artificial night light are able to carry out photosynthesis at night. 70 lx corresponds to strong street lighting. Despite these findings, there are still only a few scientific studies examining the effects of artificial lighting on plants and entire ecosystems.
Effects on animals
Nocturnal Insects and those that are active in the evening are particularly affected by artificial lighting. In flight, they orientate themselves to the UV radiation of the setting sun or the moon and are attracted by artificial lighting until they are completely exhausted. A single street lamp can attract up to a thousand insects per night. These become easy prey for light-insensitive hunters, while light-sensitive hunters are left with the rest of the light-insensitive insects. This can lead to a disruption of entire ecosystems. Other problems can arise species-specifically. Moths produce significantly fewer pheromones under light than in the dark, which limits their reproduction. Up to 70% more moths can be found under street lamps than in the dark, which even favors it. This also affects the pollination of plants. Moths contribute to the reproduction of many different plant species but transport significantly less pollen in lighted locations than in natural darkness.
Improving the situation by changing the light sources in street lighting, is controversial and no unanimous statement can be made about insect-friendly light sources at this time. In some works, LED lights are particularly positively highlighted, but in other works, they are presented as particularly harmful to some insect species.
Birds have particular problems with high light intensities. Artificial light prolongs the birds' daytime activity and leads to disorientation. Migratory birds are distracted from their routes by the light, the risk of collision increases, and birds can fall victim to predators due to disorientation. This can be counteracted by reduced lighting or flashing and stroboscopic lights, but the latter is at odds with disturbing residents.
A shift in molting was observed in songbirds. In the case of nocturnal lighting, this moved forward up to 3 weeks.
Fish also have light-sensitive species and species that are attracted to light. For light-sensitive species such as eels, illuminated dams or bridges are major obstacles. These obstacles can disrupt their routes at night, they become exhausted as they swim against the stream to avoid these obstacles. Fish that are not sensitive to light, such as salmon, are supported by lighting and can therefore more easily cross obstacles such as dams. Like insects, fish species that are attracted to light run the risk of being caught more easily.
In addition to the previous effects, nocturnal mammals develop an increased escape behavior under lighting. Moreover, artificial lighting changes the seasonal behavioral patterns of mammals by the temporal release of melatonin. This can lead to depressive behavior.
In summary, the effects of artificial lighting on plants, animals, and entire ecosystems are diverse and have only been superficially studied to date. Behavioral changes in individual species can have cascading effects on other species and have far-reaching consequences for entire ecosystems. For a more precise assessment, extensive studies and long-term research would have to follow.
 Lichtverschmutzung – Ausmaß, gesellschaftliche und ökologische Auswirkungen sowie Handlungsansätze, C. Schröter-Schlaack, C. Revermann, N. Schulte-Römer, 2020, Büro für Technikfolgenabschätzung beim deutschen Bundestag, 186
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