ARTICLE Volf_JUM_2024/IDIAP Why daylight should be a priority for urban planning Volf, Carlo Bueno, Bruno Edwards, Peter Hobday, Richard Mäder, Stephan Matusiak, Barbara Wulff, Katharina Osterhaus, Werner Manoli, Gabriele Della Giustina, Christina Joshi, Jasmin Kämpf, Jérôme Vega, Kevin Kueffer, Christoph architecture Daylight Ecosystem services Green city health Nature-based solutions Sustainability Journal of Urban Management 2024 https://linkinghub.elsevier.com/retrieve/pii/S2226585624000190 URL 10.1016/j.jum.2024.02.002 doi Daylight is essential for ecosystems and for the physical and mental well-being of people. In densely populated cities, only a small proportion of total daylight is available to support urban greenery and most people have little daily exposure to natural daylight. Despite this, many cities have followed a strategy of densification as a way of preventing urban sprawl and reducing energy consumption. In this article, we review the biological importance of daylight and show that urban densification leads to a reduction in the daylight available for both people and nature. We conclude that daylight in cities should be treated as a limiting resource that needs to be planned and managed carefully, much like water or energy. We suggest elements for a policy framework aimed at optimizing urban daylight, including how to determine daylight needs, how to determine the maximum viable urban density, and policy options for built and unbuilt areas.