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Kolláth, Z., Száz, D., Tong, K. P., & Kolláth, K. (2020). The Colour of the Night Sky. J. Imaging, 6(9), 90.
Abstract: The measurement of night sky quality has become an important task in night sky conservation. Modern measurement techniques involve mainly a calibrated digital camera or a spectroradiometer. However, panchromatic devices are still prevalent to this day, even in the absence of determining the spectral information of the night sky. In the case of multispectral measurements, colour information is currently presented in multiple ways. One of the most frequently used metrics is correlated colour temperature (CCT), which is not without its limitation for the purpose of describing especially the colour of natural night sky. Moreover, visually displaying the colour of the night sky in a quantitatively meaningful way has not attracted sufficient attention in the community of astronomy and light pollution research—most photographs of the night sky are post-processed in a way for aesthetic attractiveness rather than accurate representation of the night sky. The spectrum of the natural night sky varies in a wide range depending on solar activity and atmospheric properties. The most noticeable variation in the visible range is the variation of the atomic emission lines, primarily the green oxygen and orange sodium emission. Based on the accepted models of night sky emission, we created a random spectral database which represents the possible range of night sky radiance distribution. We used this spectral database as a learning set, to create a colour transformation between different colour spaces. The spectral sensitivity of some digital cameras is also used to determine an optimal transformation matrix from camera defined coordinates to real colours. The theoretical predictions were extended with actual spectral measurements in order to test the models and check the local constituents of night sky radiance. Here, we present an extended modelling of night sky colour and recommendations of its consistent measurement, as well as methods of visualising the colour of night sky in a consistent way, namely using the false colour enhancement.
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Meier, & J.M. (2018). Temporal Profiles of Urban Lighting: Proposal for a research design and first results from three sites in Berlin. International Journal of Sustainable Lighting, 20, 11–28.
Abstract: 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.
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Schnitt, S., Ruhtz, T., Fischer, J., Hölker, F., & Kyba, C. C. M. (2013). Temperature stability of the sky quality meter. Sensors (Basel), 13(9), 12166–12174.
Abstract: The stability of radiance measurements taken by the Sky Quality Meter (SQM)was tested under rapidly changing temperature conditions during exposure to a stable light field in the laboratory. The reported radiance was found to be negatively correlated with temperature, but remained within 7% of the initial reported radiance over a temperature range of -15 degrees C to 35 degrees C, and during temperature changes of -33 degrees C/h and +70 degrees C/h.This is smaller than the manufacturer's quoted unit-to-unit systematic uncertainty of 10%,indicating that the temperature compensation of the SQM is adequate under expected outdoor operating conditions.
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Gaston, K. J. (2013). Sustainability: A green light for efficiency. Nature, 497(7451), 560–561.
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Warrant, E. (2016). Superior vision in nocturnal insects inspires new night vision technologies. SPIE Newsroom.
Abstract: Algorithms that dramatically improve the quality of video sequences captured in very dim light have been developed on the basis of the neural mechanisms in nocturnal insects with excellent visual capabilities.
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