EL: Light and Lighting research team

Optimising night-time artificial light emissions today essentially involves reducing energy consumption, which accounts for an average of 40 % of local authorities' electricity bills. Local authorities and professionals in the sector are therefore investing heavily in this issue, in a context that is under pressure (energy crisis, adaptation to climate change). For several years now, the maturity of LEDs for public lighting has offered some very interesting opportunities compared with older lighting sources. Even though LEDs only account for 15 to 20 % of the lighting installed in France, they account for the bulk of new projects. However, there is no magic effect. If we project the recurring rise in the price of electricity over one or two decades, for example, the energy savings will only compensate for this increase. This limits the scope for local authorities to reinvest in renovation programmes. Other solutions therefore need to be investigated, such as considering the actual reflective properties of road surfaces or better adapting the amount of light to specific uses, to ensure more adequate lighting.

Adequate is used here in the sense of limited. "Is lighting always right?" is also a real question. Particularly at a time when the impact of artificial light on biodiversity is increasingly the subject of debate in scientific, professional, and political circles. There is a great deal at stake in current studies or territorial strategies to examine how human needs for light at night can coexist with the nocturnal life of other species. This subject must be dealt with without blinkers as regards the human pressure exerted on natural environments, but also without it serving as an alibi for decisions that are underpinned by certainties or financial imperatives. The EL team's work does not claim to be a comprehensive treatment of this issue. It aims to propose new tools and new knowledge to serve it so that, if the need for lighting is proven, it is useful to all users, technically controlled and responsible in the face of the challenges of ecological transition.

Whatever the mobility context, type of infrastructure or mode of travel, the perception of the environment is fundamental, and there is a consensus that the vision of different users is paramount. Infrastructure and facilities must therefore provide sufficiently visible information to enable users to navigate, maintain their trajectory or interact with other road users in complete safety. Providing infrastructure managers or local authority road services with tools for diagnosing visibility is important for maintaining a sufficient level of service and guaranteeing access to useful visual information. The problem is a complex one, since the intrinsic performance of road objects (contrast of markings and signs, luminance of traffic lights, etc.) is strongly affected by environmental conditions (day, night, weather, etc.), the complexity of the task being performed (driving, presence of other road users, etc.), the multiplicity of information present in the field of vision, personal experience, individual behaviour, and so on. Once again, the EL team does not claim to be able to provide a global solution to this broadly multidisciplinary issue, and remains focused on what it knows how to do: objective measurements of physical quantities and their interpretation in terms of visual performance. The challenge here is to ensure that the characteristics that can be managed (photometric, colorimetric, dimensional, etc.) are done so in a way that is visually optimal (contrast, visibility, absence of glare, etc.) when a facility is brought into service and then throughout its life (planning of maintenance operations). With the arrival of the autonomous vehicle and its specific vision sensors, the challenges of visual performance increasingly extend beyond human needs alone. To prepare for its deployment, we already need to consider the wider scope of this future cohabitation.