The environmental impact of artificial lighting in urban settings: gaps, challenges, and sustainable lighting design

Abstract

Artificial light has significantly impacted the value and perception of the night in individuals who apply it, those who develop technologies to supply it, those who assess its environmental impact, and those who use and benefit from it. The unnatural illumination of nightscapes has become seamlessly integrated into society's fabric, making night-time bright and over-illuminated across landscapes where the natural light (e.g. emitted by the moon and stars) is masked by Artificial Light At Night (ALAN). In this way, ALAN has become a pollutant, known as light pollution (LP), that has emerged with the exponential increase of unnatural brightness and the change in spectral composition induced by improperly managed lighting technologies. ALAN has been shown to alter light environments of nocturnal terrestrial and aquatic habitats, which can impact many organisms' physiological processes, body functions and behaviour, affecting multiple intra- and interspecific interactions and even ecosystem processes. Current technological advances in outdoor lighting have the potential to develop light pollution reduction strategies that balance conflicting societal needs and environmental concerns. However, this potential remains largely untapped due to insufficient communication between ALAN researchers and lighting practitioners. The problem of reducing LP remains complex as it involves the active collaboration between ALAN researchers and lighting practitioners and a lingua franca between experts involved to transfer and translate research into practice. This thesis addresses the environmental impact of artificial lighting in urban settings, including existing communication and knowledge gaps, challenges posed by artificial light in aquatic realms and future perspectives towards sustainable lighting design. To mitigate the communication gaps between ALAN researchers and lighting practitioners, I propose a transdisciplinary framework between the experts in the practice, research, production, policy-making and planning of light and lighting. In collaboration with experts from ALAN research and the lighting practice, I suggest a four-step process to aid in establishing collaboration between the domains involved. Moreover, to set a shared understanding between ALAN research and the lighting practice, I propose a collaborative systematic review to aid in the transfer of diverse responses of plants, arthropods, insects, spiders, fish, amphibians, reptiles, birds, and non-human mammals (including bats, rodents, primates, and ungulates) when exposed to ALAN. As well as a mutual agreement on key terms set by representatives from both domains. The systematic review is based on finally 216 studies reporting behavioural and physiological responses across six relevant organism groups. To transfer the results between the research and the lighting practice, collaborative discussions between the experts of each domain resulted in establishing an ALAN lingua franca on key terminologies and definitions related to natural and artificial light as knowledge both domains should acquaint. The collaborative discussions also included a common language on relevant radiometric and photometric parameters that ALAN researchers must consider in their research and lighting practitioners in their day-to-day lighting practice. Also, the discussions led to the proposal of two communication strategies: a communication framework and a knowledge infrastructure scheme to set an ecological ceiling of awareness (responses to avoid) and a lighting foundation (essential knowledge to gain) for a better flow of information between the domains involved. The findings of this study also indicated that aquatic organisms and their realms remain understudied and that further studies on the impact of ALAN on aquatic habitats and their inhabiting biodiversity are needed. Furthermore, I explored the potential implications of bridge illumination on a river transect to confront the existing knowledge gap on the potential impact of ALAN on riverine systems with illuminated bridges. The light field of a river was quantified from a research vessel considering seven illuminated bridges. The results indicated that LP was induced by surrounding illumination and bridge illumination. Via a conceptual model, the unnatural light scenarios at illuminated bridges and their potential impact on the life history of two migrating fish species, Atlantic salmon and European silver eels, were addressed. Additionally, at the same river transect and illuminated bridges, patterns of polarised light pollution (PLP) reflecting at the water's surface were quantified near the illuminated bridges and their potential effects on aquatic insects were discussed. The findings of the four studies highlight the need for (i) better communication frameworks between experts of ALAN research and the lighting practice, (ii) transdisciplinary interfaces and collaborations to efficiently translate ecological research into the lighting practice, as well as the need for (iii) quantified ALAN and PLP across inland waters to develop sustainable lighting solutions to preserve riverine nightscapes. This thesis provides communication frameworks to bridge communication gaps, a knowledge infrastructure scheme to mitigate the transfer of knowledge between the domains, evidence on LP and PLP induced by surrounding and bridge illumination on a river transect, together with a conceptual model on ALAN as a potential barrier for migrating fish. Additionally, this thesis discusses transdisciplinary approaches, perspectives inclusive of natural environments, and a vision towards lighting approaches that require an urgent change and concludes with recommendations for the future of ALAN research and the lighting practice.