The Nachtlichter project (part of “Nachtlicht-BüHNE”, funded during 2018 to 2022 by the Helmholtz Association of German Research Centres) aimed to collect information on artificial light sources at night. This was done as a cooperation between researchers and citizen scientists, who worked together at all stages of the project, including development of an app, data collection and analysis. The active Participation in all stages is to be highlighted as a special feature of the project. During the data-collection-campaigns, more than 200 people worldwide counted over 250,000 lights, covering an area of around 22 km2. Furthermore, the project strengthened public awareness on the topic of light pollution, and a deeper understanding of the problem was developed by the participants.