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Natural sources of lighting are a major environmental cue that help structure ecological systems, yet these are undermined by artificial lighting which disrupts key processes such as migration, pollination and reproduction. Despite knowledge of diverse impacts and a huge shift towards LED street lighting, conservation practitioners are struggling to respond. We present key findings from a research collaboration between the University of Bern and the Swiss Federal office for the Environment, which aimed to identify practical ways to reduce the ecological impacts of artificial lighting. This project involved a review of the data available on Swiss lighting, a review of the known impacts of artificial lighting on national priority species, and spatial modelling to identify particularly light-sensitive locations. Undertaking such an analysis at a national level had the advantage of bringing the data and research gaps into sharp perspective. We found that in practice, the data used by local governments to manage lighting is typically a database of lamp locations, which also includes entries for lamp type, wattage and height. No national lamp inventory exists, and records for all private sources of lighting (associated with hospitals, commercial and industrial areas) are missing. Other sources of information such as VIIRS satellite data are occasionally used, but only as a broad emission indicator. Some attempts have been made at aerial night photography, but images remain uncalibrated and therefore useful primarily as indicators of bright lighting locations. Nothing is known about the impacts of artificial lighting on the majority of species identified as priorities for …