Space after dark: Measuring the impact of public lighting at night on visibility, movement, and spatial configuration in urban parks

On 19 August 2016, Transport for London (TFL) launched their first Night Tube, which offers 24-hour service on Fridays and Saturdays. With more lines coming in autumn 2016, London follows the lead of other cities such as New York, Berlin, and Tokyo to be deemed a 24-hour city. Aside from debates concerning the energy waste, pollution, and security caused by the policy, one question is evident: How does the city 'work' at night? Humans navigate through space using vision which involves cue or landmark recognition, turn angle estimation, network comprehension, and route plotting strategies (Golledge, 1995). The situation changes at night when the configuration of space is altered by the presence of artificial light. This applies predominantly to outdoor spaces where lighting designers or urban planners classify the type of luminaires according to the street hierarchy: white light is used for the 'core' areas and main roads, yellow light for secondary roads, and reddish light for residential pathways (Meier, 2015, p.251). This study aims to explore whether or not there is a change of selected or most frequently used routes due to the impact of altered visual perception of space, and how the locus and quantity of the artificial illumination may change the perceived urban structure. It uses Dalton's (2001) research on cognition and movement, and the theory of natural movement (Hillier et al., 1993) as a base. Two parks in London were selected as the main case studies: Green Park and Clapham Common, along with a pilot project in The Meadows, Edinburgh. The parks were examined using a combination of street network analysis, detailed observations on people's movement and occupancy patterns, and survey on the existing lighting conditions. Correlations between movement, space, and lighting were analysed using 'multiple linear regression' method to discover a link between the fields of urban planning and lighting design. The results reveal that artificial illumination at night alters the perception of the spatial configuration. These results may contribute to the development of lighting master plans in cities. The research presented here produces parallel results with a recent study by Del-Negro (2015) that reveals how the lighting situation affects people's choice of routes through a series of experiments conducted in Lisbon and London. The correlation between Normalised Angular Choice and illuminance values suggests that these two factors are reliable predictors in an urban configuration at night, which allows us to use the illumination factor as a variable when applying Space Syntax analytical methods to predict nocturnal movement patterns.