Impacts of urban morphological characteristics on nocturnal outdoor lighting environment in cities: An empirical investigation in Shenzhen
Introduction
In high-density urban contexts, there is an emerging trend of outdoor living among urban residents in recent years. More and more people tend to stay outside for the purposes of experiencing nature, conducting businesses and inspiring their social life [[1], [2], [3], [4]]. Over the past four decades of rapid urbanization and densification in Asia, multiple types of public spaces in cities have become “outdoor living rooms” for urban residents [[5], [6], [7]]. Under these circumstances, better designed outdoor spaces with more humanized environmental conditions are of great importance in urban planning and design. Lighting, including both natural daylight and night-time artificial lighting, is a vital environmental element that affects people's outdoor activities and the creation of liveable neighbourhoods in cities [[8], [9], [10], [11]]. Experiencing and enjoying the “time of night” is a tradition and an important part of human life. Moreover, appropriate lighting for outdoor spaces in cities can benefit people's social well-being [12]. The phenomenon of the “night-city” (yeshi) can be traced back to as early as the ancient China's Song Dynasty a thousand years ago, when the Song court abolished curfew (xiaojin) and gave the freedom to be out during the “time of night” to citizens [13]. According to Dongjing Meng Hua Lu (Dreams of Splendour of the Eastern Capital), the brightly lit (denghuo tongming) outdoor environment at night enabled the forming and maintaining of a safe and dynamic night-time in the Song capital city of Bianliang (Kaifeng) [14]. Back to the modern-day, night-time outdoor lighting behaviours have been proved to have significant effects on energy consumption, neighbourhood vitality, and human well-being in relation with safety, health, convenience, comfort, aesthetics and sustainability [[15], [16], [17], [18], [19], [20], [21], [22], [23]].
In the era of rapidly transforming cities with high population density, several researchers have demonstrated the significance of night-time lighting design for urban sustainability and enhancing social well-being in the city. Previous studies have examined outdoor night-time lighting conditions in urban residential areas and identified a few issues, including low lighting levels, low illuminance uniformity, wasted lighting energy, glare interference, light intrusion, light scattering, and excessive light output. There are several forms of urban neighbourhoods in cities, and these have diverse morphological patterns. However, few scholars have systematically studied the night-time lighting behaviours of neighbourhood-scale outdoor space based on real-time baseline data collection in real urban contexts with different morphological characteristics and spatial components. Besides, to a substantial extent, outdoor night-time lighting conditions are significantly impacted by urban morphological patterns, particularly the building densities and spatial geometry, via light scattering and light reflection. Consequently, urban design's specific elements and criteria to enhance outdoor night-time lighting quality are relatively absent in the currently implemented standards and assessment systems. Besides considering the functionality and safety of night-time lighting in urban spaces, it is also necessary to consider the dimension of urban morphological features that contribute to creating a comfortable, safe, and energy-efficient night-time outdoor space in cities.
The present paper conducts an empirical study of multiple types of urban neighbourhoods' outdoor night-time lighting environments by examining the relationships between urban morphological aspects and outdoor night-time lighting behaviours. The paper aims to 1) evaluate the advantages and problems of the outdoor lighting environment during the night-time in different forms of urban neighbourhoods; 2) identify some critical urban morphological descriptors influencing outdoor night-time lighting behaviours. By adding the dimension of urban morphology, this research's findings offer insights into the setting of more specific criteria for urban design and renewal and subsequently, contribute to healthy city initiatives by enabling the attainment of a more optimal trade-off between outdoor visual comfort and lighting energy savings in the night-time (Fig. 1).
Section snippets
Existing studies of nocturnal outdoor lighting in cities
As a critical issue of urban sustainability, the night-time performance of outdoor lighting has been a subject of much concern and extensive research over the last century regarding energy consumption and savings, light pollution, and the impact on urban and rural ecosystems, and urban social well-being.
Study area
As an “experimental field” for testing China's Reform and Opening-up policy, the Shenzhen Special Economic Zone (SEZ) has been widely recognised as China's “model city” for urban study. During the past four decades' unprecedented development and redevelopment, Shenzhen has exhibited and highlighted many socio-ecological phenomena and urban problems that can be found in other cities across China [[67], [68], [69], [70], [71], [72]]. This study takes Shenzhen as a critical case study of a rapidly
Night-time outdoor lighting conditions - descriptive analysis
The results reveal that significant night-time horizontal illuminance level (N-HIL) variation between different night-time hours (19:00 p.m.~22:00 p.m.) within each tested site was not observed in this research, while the dramatic differences of the night-time lighting conditions among the sites were captured (Fig. 4). Site E and F exhibited the lowest average night-time illuminance level (avg. N-HILE = 1.7 lx, avg. N-HILF = 1.3 lx), which did not meet the minimum requirements of both CIE
Influence of urban morphologies on night-time illumination distribution
The present research has shown that there are significant variations of the night-time lighting behaviours among the 11 tested sites, which were significantly affected by their distinct morphological characteristics. During the night-time, some of the tested sites with a higher BCR but a lower SVF (such as Site A, D, and H, rather than Site F) tended to present a higher outdoor illuminance level than those with a higher degree of spatial openness (such as Site C and E, rather than the Site YN,
Conclusion and future study
This paper has presented the effects of multiple aspects of urban morphological characteristics on outdoor night-time lighting behaviours by measuring 11 open urban neighbourhood units that reflect the variety of the prevailing urban morphological patterns in city centres of Shenzhen. A set of urban morphological descriptors (UMDs) and two outdoor night-time lighting parameters were statistically analysed via Pearson's correlation and multivariable linear regression. Several outdoor lighting
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This paper was developed from parts of the first author's doctoral research project. The authors would like to thank the anonymous reviewers for their comments that helped to improve the manuscript. The authors also thank the residents of the investigated neighbourhoods for their permission and assist during the on-site measurement. The Shenzhen Center for Design also shared the related maps and site information of the Hubei village neighbourhood to support urban morphological analysis in this
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