The extreme spread of artificial light sources continuing since the establishment of electric light in the 1880s gives more and more importance to an unintended consequence of this development – the so-called light pollution. This term describes the brightening of the night sky by artificial light as an unwanted side effect of private and public lighting of streets, paths in parks and watersides, decorative or commercial illumination or light art. Particularly above large cities, so-called light domes evolve which are ever expanding in the course of urbanisation and rural sprawl.

Within the framework of the TA project, the biological, ecological, health-related, sociocultural and economic impacts of artificial lighting at night have been examined. The present working report provides an overview of the state of knowledge with regard to the extent, current development trends and impacts of light pollution. On this basis, options for action are presented that will contribute to a reduction of light pollution taking also into consideration the beneficial objectives of lighting. Thus, the debate on the pros and cons of artificial lighting at night shall be intensified and an evidence-based political support of ongoing developments with regard to lighting design and technology shall be enabled.

Key results

Based on satellite data, a worldwide increase in the area illuminated at night and in the intensity of illumination of about 2 % per year each can be observed. In many rapidly developing countries in Africa, South America and Asia, the increase is above average, whereas in already brightly lit countries, such as e. g. Germany, it is often only moderate. Within Germany, most of the Länder show increasing values both for the illuminated area and for the intensity of the illumination – Bavaria and Schleswig-Holstein being particularly noteworthy.

On the one hand, medically relevant effects of light at night result acutely from suppressing the release of the hormone melatonin, which is involved in the regulation of sleep and the temporal coordination of many body processes. On the other hand, these effects result from the associated disturbance of the (circadian) rhythm – which is characterised by the change of day and night within a cycle of 24 hours – of the body᾽s own metabolic processes. Studies in sleep labs have shown that both acute and circadian light effects can lead to physiological states that are similar to a clinical manifestation – e. g. that of diabetes or cardiovascular disorders. It is unclear, however, from which extent the shift in circadian rhythms poses a threat to health. This is why there are no thresholds or reference values for light intensities or for the extent and duration of the temporal shift.

Animals and plants depend on regular differences in their light environment to synchronise their seasonal and diurnal behaviour. Moreover, two thirds of all invertebrates and one third of all vertebrates are nocturnal species and thus directly affected by a brightening of night landscapes. Depending on the species, different effects of light pollution occur. Thus, artificial lighting can cause behavioural changes, e. g. a temporal shift of hunting, resting or reproduction phases. The local radius of activity of individuals can also be changed if e. g. insects are attracted by artificial light sources or if illuminated areas are avoided by animals. There are major differences between individual species with regard to spectral sensitivity. In general, the number of species affected and the extent of the effects increase the brighter the lighting and the higher the blue and ultraviolet spectral components. Plants react to artificial lighting, e. g. with a delayed leaf shedding or altered flowering times, so that frosts can damage the plant tissue or the synchronisation of flowering with the occurrence of pollinators can be impaired.

In Germany, there are some starting points in the fields of immission control, nature conservation and urban land use planning that can be referred to for a stronger regulation of artificial lighting at night. At the local level, municipal lighting statutes or lighting master plans can be used both to initiate a public debate on the negative side effects of artificial outdoor lighting and to provide guidance for the design of public and private lighting systems. In order to strengthen possible regulatory approaches, however, we should not wait for the complex research of relevant parameters and thresholds. To counteract the trend of brightening night landscapes, light emissions should rather be assessed in a precautionary manner. Based on this, guidelines for action can be concretised using current knowledge and state-of-the-art technology. In doing so, it is also possible to benefit from the experience of other European countries. Thus, measuring and monitoring systems could be established to monitor the development of artificial lighting, e. g. by the mandatory use of a lighting cadastre. The Länder and local authorities would benefit from the provision of guidance to remove legal and planning uncertainties, e. g. with regard to the significance of industry standards for street lighting. For federally owned buildings and facilities, lighting guidelines could be developed and implemented to minimise light pollution. The development of integrated local and regional lighting concepts can be advanced by means of funding programmes, awards and competitions for sustainable lighting. Finally, limit and guide values could be established as a basis of assessment in order to be able to evaluate light emission protection in already existing formal planning and control instruments. It is also worth considering the possibility of an independent regulation to limit light pollution.