Abstract
In April 2020, due to the coronavirus pandemic and the tourism decrease in Cracow (Poland), the Road Authority of the City of Cracow, followed by the authorities of several neighbouring municipalities, decided to turn off street lighting at night. It is worth noting that this is the first time that street lighting has been turned off in such a large area on a longer time frame at this scale, including one of the most populated cities in Poland, which made it possible to make unique observations. During this period, with the help of small night-sky radiance meters (Sky Quality Meters (SQM)), many ground-based measurements were made, both within the city and in its vicinity. For this purpose, the existing light pollution monitoring stations in Cracow and neighbouring cities were used. It was found that after switching off street lighting, the zenith surface brightness of the cloudless sky decreased by 15–39%, and this value was proportional to the city’s population. The night-time light satellite data (VIIRS/DNB) on radiance from Cracow and neighbouring communes were also analysed, both their daily values as well as monthly and annual averages. It was found that in the case of a large city such as Cracow, turning off all street lighting reduces the amount of light energy radiated into the sky by about 50%, which is a relatively small decrease in radiance, while reducing the surface brightness of the night sky by about 40%, regardless of the state of the atmosphere. The effect of a significant decrease in radiance as a result of switching off street lighting was found in each of the analysed communes, especially the urbanised ones.
Highlights
Given that outdoor activities decreased by up to 90% during a lockdown, these results indicate that the light output of the city seems to be dominated by permanent lighting that does not adapt to the real use of the outdoor areas by the citizens
All visible infrared imaging radiometer suite camera (VIIRS)/Day–Night Band (DNB) images are presented in the EPSG coordinate system: 4326—WGS
The analysis of VIIRS/DNB data showed that in each of the researched communes switching off street lighting significantly decreased the radiance
Summary
From the very beginning of the problem of light pollution, especially in the form of an artificial night sky glow, it was obvious that the main sources of this problem were cities, street lighting [1,2]. The concept of a light glow was first introduced probably in 1935 [3], and the concept of astronomical light pollution in 1973 [4]. Along with the development of urban infrastructures, in addition to street lighting, other light sources appeared, increasing the brightness of the sky glow. Light pollution is mainly due to the operation of wrongly designed street lighting, advertising, illumination of sports stadiums, construction, security, and façade lighting [7,8,9,10,11]. There is no real effective policy that deals with this problem
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