For billions of years, the Earth’s rotation on itself has resulted in the invariable succession of day and night on its surface. This natural alternation has profoundly shaped the evolution of living organisms through morphological, biological, and behavioural characteristics that enable many species to live, find their bearings and communicate in the darkness on which their survival largely depends.
In recent decades, however, massive and growing urbanisation has been accompanied by an increase in artificial night-time lighting (homes, street lights, car headlights, illuminated signs, etc.). While it poses problems for stargazing and raises concerns about human health, light pollution is first and foremost a threat to biodiversity. It is a major factor in the disappearance and fragmentation of natural habitats, but also in the direct mortality of species that live at night.
In our quest to preserve biodiversity and the integrity of ecosystems, the emergence of the concept of the Black Frame represents a crucial milestone. It appears to be a response to the challenge of light pollution, an essential approach to the long-term stability and resilience of ecosystems, and a new strategy for moving from observations to action. Beyond this, it represents a major economic and social challenge for many stakeholders.
What is the black infrastructure?
Whether green, blue or black, ecological corridors provide a natural link between different habitats, enabling animal and plant species to move freely, migrate, feed, reproduce or rest. Their aim is to preserve and restore an ecological network that is conducive to maintaining biodiversity. Unlike its sisters, the green (terrestrial) and blue (aquatic) infrastructure, the black infrastructure includes areas of darkness necessary for nocturnal life.
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Light pollution, a threat to biodiversity
To fully understand the issues surrounding the dark infrastructure, we need to understand the impact of artificial lighting at night on animal and plant species. Light pollution represents a real danger for these species, which are largely dependent on the alternation of day and night, and some of which are exclusively nocturnal for all or part of their development cycle. Its power of attraction or, conversely, repulsion, particularly affects the mobility of animals and disrupts the reproductive and migratory behaviour of certain species, threatening their survival. It can also have irreversible physiological effects (illness, weakening).
As well as being more exposed to predators, some species of photophilic insects and birds orient themselves according to the stars or the moon. Attracted by artificial light, they lose their bearings and fall prey to ecological traps. Stuck in a hostile territory without ever being able to find their way back, they generally die of exhaustion. Most insects also perish, burnt by the heat of the lamps. Artificial light is the second biggest cause of insect extinction after pesticides.
In fireflies, for example, this light pollution seems to disturb the males in their search for females. When, by chance, they do manage to find them, it seems that they are still waiting for a night that will never fall before mating. In contrast to photophilic species, photophobic species, such as bats, avoid light, which forms an insurmountable barrier and fragments their habitat.
But these are not the only species to suffer from light pollution: moths, amphibians, spiders, nocturnal birds of prey, deer, aquatic species, and plants are also affected. During their seasonal migration, toads are reportedly unable to cross illuminated roads or to transit from their wintering grounds to their breeding grounds. Darkness also affects the metabolism and development of plants.
Artificial light triggers premature flowering, for example, which makes the plant vulnerable to frost later on. Too much light can cause stress in certain plant species and lead to the development of diseases. Pollination also takes place mainly at night, obviously in the presence of pollinating insects.
The same applies to the life cycles of these many species (feeding, reproduction, migration, development, prey-predator relationships, etc.). It should also be noted that in humans, artificial night-time lighting disrupts circadian rhythms and the production of melatonin, which is necessary for sleep. Reduced sleep quality is recognised for the risk of pathologies that it engenders (illness, general weakness).
The black infrastructure, an environmental necessity
When the Blue and Green Infrastructure Policy was launched in 2007, light pollution was not yet considered to be a major issue, and was not considered, if at all, in the identification of ecological continuities. Today, the barrier effect of artificial light at night and its consequences for the increasing degradation of flora and fauna have been demonstrated and recognised. It has therefore become essential to preserve and restore an ecological network that encourages nocturnal life: the black infrastructure.
In its guide “Trame noire, méthodes d’élaboration et outils pour sa mise en œuvre“, designed to encourage the development of the black infrastructure in French territories, the French Office for Biodiversity (OFB) defines the concept as “a connected set of biodiversity reservoirs and ecological corridors for different environments (networks), the identification of which takes into account a sufficient level of darkness for nocturnal biodiversity”. The Black Infrastructure becomes a complete and complementary approach to the Green and Blue Infrastructure and is fully in line with ecological continuity.
There are a growing number of initiatives to identify these black infrastructures to preserve the areas of darkness necessary for life at night. Other initiatives are aimed at restoring these areas through the rational management of artificial lighting at night. The city of Lille, one of the pioneers in this field, is a case in point with its black infrastructure project. Other examples include the town of Douai (dark infrastructure project) and the Pyrenees National Park (black infrastructure project).
What methods should be used to draw up the Black Infrastructure and what tools should be used to implement it?
The Grenelle laws of 2009 and 2010 enshrined the prevention, reduction, and limitation of light pollution in the Environment Code. The regulatory framework for lighting management in France is set out in a series of decrees and ministerial orders: Decree 2011-831 of 12 July 2011 on the prevention and limitation of light pollution, Decree 2012-118 of 30/01/2012 on outdoor advertising, signs and pre-signs, Law 2016-1087 of 8 August 2016 for the reconquest of biodiversity, nature and landscapes and the Ministerial Order of 27 December 2018 on the prevention, reduction, and limitation of light pollution.
This regulation of lighting management is, however, carried out independently of the Black Infrastructure. Over and above these regulations, artificial lighting at night must therefore be the subject of particular attention within ecological continuities.
An OFB guide to the Black Infrastructure and the fight against light pollution
In its guide, the the French Office for Biodiversity (OFB) proposes definitions, methods and concrete tools illustrated by feedback. It makes recommendations along 3 axes: technical, temporal, and spatial.
Technical
This involves acting on the characteristics of luminaires (height, spectrum, flux, etc.). The OFB recommends, for example, giving preference to lights emitting in a narrow spectrum to “mechanically reduce the number of species and biological functions impacted”. It also recommends avoiding or reducing as far as possible harmful wavelengths such as blue light. Blue light is particularly attractive to nocturnal insects, which form the basis of the food chain. It also disrupts biological clocks and has an impact on human health.
Summary of recommendations:
- Avoid or eliminate unnecessary street lights.
- No light should be emitted above the horizontal.
- The height of masts should be as low as possible to reduce their visibility to wildlife.
- Light only the useful surface on the ground.
- Emit as little light as possible, with the narrowest possible spectrum and located in the shade, to reduce glare for wildlife as much as possible.
Certain human activities may justify the exceptional presence of night lighting within ecological continuities. In these cases, the guide lists the characteristics that need to be considered in lighting management, over and above the regulations.
Temporal axis
This involves planning the lighting over time (times, duration, etc.) and adjusting it throughout the night – from dusk until dawn, when most nocturnal animals are very active – by targeting the times when it is necessary. It should be noted that switching off lighting in the middle of the night would be particularly beneficial for flora and species heading towards the starry sky (migratory birds, for example).
Various technologies for managing street lighting (switching on and off) can be adopted. These include conventional clocks and astronomical clocks, which can be used to switch off at a fixed time or according to sunrise and sunset respectively. Photoelectric cells react and adapt lighting to ambient brightness. Finally, presence detectors trigger the lighting when a vehicle or person passes by.
Spatial axis
This involves adapting the spatial organisation of light points (density, position, etc.). To achieve this, the OFB recommends a differentiated management of lighting, characterised by a reduction in the density of light points, or even their total elimination, in ecological continuities and in sectors identified as being at risk. Floor coverings should also be considered. Depending on their capacity to absorb the light emitted, they can reflect a large proportion of it back towards the sky. “To reduce the impact of light on biodiversity in key sectors, it is (therefore) preferable to choose materials with a low reflection coefficient under the luminaires to reduce this reflection towards the sky”.
Summary of recommendations:
- Do not illuminate watercourses.
- Do not illuminate adjacent natural areas.
- Maintain dark interstitial spaces between lampposts to allow wildlife to cross.
- Use flooring with a low reflection coefficient under lighting.
Cerema factsheets for restoring nightlife in ecological continuity
Cerema also offers a series of 7 comprehensive technical fact sheets: Planning, Urbanism, Biodiversity, Lighting, which are especially useful in view of the issues we will discuss below. They cover:
- Integrating biodiversity into lighting planning and maintenance.
- Adapting lighting to local biodiversity issues.
- Integrating night-time biodiversity issues into planning and operational tools.
- Choosing a lighting source by considering the impact of its light spectrum on biodiversity.
- Understanding the ministerial order of 27/12/18 on light pollution.
- Understanding the regulations, standards and recommendations for outdoor lighting and advertising.
- Improving the acceptability of lighting modulation through public participation, consultation, and co-construction.
Tools for local authorities and the development of the Black Infrastructure
Local authorities can incorporate their approach into master lighting schemes, territorial coherence schemes (SCoT in France), Local Urbanism Plans (PLU in France) or regional schemes for development, sustainable development, and territories equality (SRADDET in France), in particular.
Tools such as the Communal Biodiversity Atlas (ABC in France) – which provides a better understanding of the biodiversity in a given area and identifies the actions to be taken – or contractual tools with private stakeholders, such as the Authorisation for Temporary Occupation of the Public Domain and the Real Environmental Obligations (ORE in France), are also invaluable in carrying out long-term actions to promote nocturnal biodiversity and mobilise the various stakeholders.
The Black Infrastructure: what are the challenges for public lighting?
For local authorities, the Black Infrastructure approach is all the more interesting because it brings together a number of issues: ecological, human health, but also energy and economic. On these last two points, the French Office for Biodiversity (OFB) cites the example of local authorities in the French Regional Nature Park of Gâtinais, where switching off lights for 6 hours a night has reduced their electricity consumption by around 40% and cut costs by almost 35%.
However, adopting lighting practices that are more respectful of nocturnal biodiversity can raise several challenges in terms of safety (for pedestrians), resistance to change and the balance between conservation and urban development. In this respect, the Black Infrastructure approach must be integrated into all land-use planning projects.
In addition, in the same way as for the Blue and Green Infrastructure policy, the establishment of a Black Infrastructure must be concerted and take into account the opinions of all stakeholders. The feeling of insecurity linked to darkness is an example of a barrier to the acceptability of a change in night-time lighting habits (switching off in the middle of the night or reducing the intensity).
Studies and surveys can therefore be carried out to find ways of improving acceptability. Awareness-raising, information, and promotion campaigns, via the local newsletter or website, workshops, public meetings, conferences or discussions with biodiversity and health professionals, for example, also play an essential role in gaining acceptance for a Black Infrastructure approach.
The Black Infrastructure: where ecological, economic and social issues meet.
Against a backdrop of increasing urbanisation, the Black Infrastructure has become a major challenge in the face of the disappearance and fragmentation of natural habitats. It is essential for preserving nocturnal species, but also other species, including humans, whose balance and health largely depend on the alternation of day and night.
For local authorities in particular, it is a planning tool that can be used both to preserve nocturnal ecological corridors and to take action on the management of artificial lighting, a fantastic opportunity to reduce risks to human health, cut energy consumption and, ultimately, work effectively in favour of living things.
