Temporal Profiles of Urban Lighting: Proposal for a research design and first results from three sites in Berlin

This paper presents and experimentally applies a research design for studying the temporal dimension of outdoor artificial illumination in complex lightscapes such as those of urban centres. It contributes to filling the gap between analyses of high-resolution aerial imagery, which provide detailed but static information on the spatial composition of lightscapes, and existing methods for studying their dynamics, which measure changes at high levels of aggregation. The research design adopts a small-scale, detailed approach by using close-range time-lapse videos to document the on/off patterns of individual light sources as the night progresses. It provides a framework and vocabulary for discrete and comparative analyses of the identified temporal profiles of lighting. This allows for pinpointing similarities and differences among the dynamics of different places, nights or categories of lighting. Its application to three case studies in Berlin indicate that switch-on and switch-off times are clustered, resulting in static and dynamic phases of the night. Midnight is a temporal fault-line, after which full illumination ends as portions of the illumination are extinguished. Switch-off times and -rates differ among the three lightscapes and, especially, among four functional types of lighting that were differentiated: infrastructural and commercial units largely remain on all night, while substantial portions of architectural and indoor lighting are switched off, though at fairly different times. Such findings are valuable for studies based on data collected at specific points in time (aerial imagery, measurements), for informing and monitoring temporally oriented lighting policies, and for understanding urban dynamics at large.