Renovating outdoor lighting: biodiversity, black screens and the photobiological impact of lighting on humans

October 2021

Agence pour l’Environnement et la Maîtrise de l’Energie (ADEME)

The subject of many economic, political and environmental issues, outdoor lighting, and in particular its management in public spaces, now appears to be a competence in its own right. For the past fifteen years, the price of electricity has been rising steadily, putting a strain on local authorities’ budgets, which amount to 1 billion euros per year in France. With an ageing and energy-intensive lighting stock, the territories have been addressing the issue for several years in order to limit consumption and therefore energy expenditure. Some have implemented coherent and ambitious renovation programmes on their own or on an inter-municipal scale. Despite the 500 million euros of annual investments made by local authorities to renew and modernise their public lighting systems, consumption remains high and the efforts made must be increased. Public lighting is now at the heart of the expectations of citizens, who are increasingly concerned about the way in which the city is administered, but also increasingly involved in environmental protection. Public lighting is a source of light pollution that contributes to the fragmentation of natural habitats. Intelligent management of lighting is therefore essential. The technological tools for this management already exist.

In addition, new needs are emerging in our territories: video protection, wifi terminals, electric vehicle charging stations, etc. Lighting infrastructures are increasingly in demand and should eventually become one of the means of pooling equipment for these new needs.

This is why it is becoming urgent to accelerate the renovation of the network and to make it communicative with a view to the development and planning of future intelligent territories. Public lighting is one of the major players in the ecological transition and a lever for action to limit light pollution and energy consumption. This guide published by ADEME should enable readers to gain a better understanding of the public lighting stock, to better grasp the issues at stake and to become players in its transformation.

To download : ademe-eclairage-exterieur-2021.pdf (3.9 MiB)

Biodiversity, black grids

According to the French Office for Biodiversity (OFB), in France, the Ministry of Ecological Transition and local authorities are implementing a public policy aimed at combating the fragmentation of natural habitats: the green and blue grid (TVB). This concept appeared in 2007 during the Grenelle Environment Forum. It allowed biodiversity to be taken into account in land use planning via ecological continuity.

As a result of this awareness, the black grid takes into account the impact of lighting on fauna, flora and ecosystems, as well as the degradation and fragmentation of natural habitats at night. The OFB defines the black grid as « a connected set of biodiversity reservoirs and ecological corridors for different environments (sub-trames), the identification of which takes into account a sufficient level of darkness for nocturnal biodiversity ». This black grid must be identified, preserved and restored.

Conceptually, the black grid is a means of recognising the temporal dimension of ecological processes. Indeed, the activity of fauna is cyclical on a daily scale, we speak of a nycthemeral rhythm. Of all animals, it is estimated that about 30% of vertebrates and 65% of invertebrates are, in whole or in part, nocturnal. This periodicity can give rise to very specific problems of fragmentation due to artificial light, which vary according to the time in the daily cycle and the species concerned.

« The black grids combine lighting master plans with environmental studies in order to define friendly lighting and maintain a balance between night-time activities and respect for the environment.

As early as 2011, the Concepto agency developed a black grid within the Rennes sdal with maps of darkness, choices of light spectra, dimming, extinction, lighting typology, heights of lights, framing of what is lit, etc., in order to limit as much as possible the impact of lighting on biodiversity. Since then, many other black grids have been identified at the instigation of cities (Douai, Nantes, Amiens, Limoges, etc.), consultancy firms or managers of natural areas (regional nature parks, national parks). Today, France is at the forefront of the world with this concept of the black grid, as it is also in terms of regulations against light pollution.

Photobiological impacts of lighting on humans

An ANSES report of May 2019 highlighted the biological impacts of light emitted by LEDs on human health: let us mention in particular the effects related to the temporal modulation of light, glare, effects on the retina and disruption of the circadian rhythm.

A. Temporal modulation

LED light sources are very sensitive to fluctuations in their supply current and can therefore exhibit variations in the intensity of the light they emit, known as « temporal light modulation ». It varies according to the quality of the electronics associated with the LED and can be perceptible. Three visual phenomena are identifiable: flicker, stroboscopic effect (apparent immobility or slowing down of a moving object) and ghost network effect (vision of multiple images during eye movements) which can induce a sensation of discomfort, or even a distortion of vision that can be accidental, in the same way as the lack of light or glare. Even when not visible, modulation at a frequency of 100 Hz can trigger migraines, thus reducing visual performance.

B. Glare

Disability glare, which corresponds to a reduction in visual performance caused by significant light scattering in the ocular media, is taken into account in the NF EN 13201 standard.

However, the International Commission on Illumination concluded in 2013 that a new glare assessment system was needed to better take into account LED lighting, especially for outdoor use. Since the advent of LEDs, discomfort glare, the feeling of discomfort experienced by an observer in the presence of very bright sources in their field of vision, has been incorrectly taken into account in EN 13201. Glare is also caused by private outdoor lighting, lighting of sports facilities, commercial and industrial areas, vehicle lighting, signs and illuminated advertising.

C. Effects on the retina

Effects on the retina are limited in outdoor lighting because the light sources of outdoor luminaires are usually located at distances greater than several metres from the retina of the user. In the case of a possible smaller distance between the retina and the light source, the photobiological risk group of the luminaires should be 0 or 1, assessed according to EN 62471.

D. Disruption of the circadian rhythm

Exposure to light at night delays the biological clock, thus affecting physiological functions such as sleep. This effect is greater when exposure is intense, prolonged and when the light is rich in blue light.


To go further

bibliography (french)

  • Dépenses énergétiques des collectivités locales, ADEME, Caisse des Dépôts, FNCCR, AITF, CEP. 2019.

  • Guide de l’élu local et intercommunal. Éclairage public. FNCCR. 2021.

  • Publications de l’Association française de l’éclairage relatives à l’éclairage extérieur.

  • Trame noire - Méthodes d’élaboration et outils pour sa mise en œuvre, par Romain Sordello, Fabien Paquier et Aurélien Daloz. Publié par l’Office français de la biodiversité, mars 2021.

  • Annexe SSL : Solid State Lighting, Association internationale de l’énergie.

  • Les défis de l’éclairage public, par Roger Narboni, Concepto, et Fanny Guerard, responsable éclairage public, smart city et environnement, ville d’Asnières-sur-Seine. Territorial Éditions. 2021.