Characteristics of light pollution - A case study of Warsaw (Poland) and Fukuoka (Japan).

Artificial light has been present in human life for decades but our knowledge of its effects is still insufficient. Lighting lets us be active longer, gives us a sense of security and provides aesthetic experiences. Despite all of these advantages, in urban areas artificial light also has a negative effects on the environment and human life. Although light pollution is one of the most common forms of anthropogenic environmental change, this phenomenon remains insufficiently investigated. The present work thus focuses on night sky brightness and artificial factors impacting the level of the phenomenon using Warsaw (Poland) and Fukuoka (Japan) as an example. The basis of the study is the new World Atlas of Artificial Night Sky Brightness. Moreover, we used image data from the Visible Infrared Imaging Radiometer Suite Day/Night Band and data from field research to analyse the primary artificial light characteristics in the two cities: illumination, colour temperature, peak wavelength, dominant wavelength, stimulation of photoreceptors, design of lighting fixtures and radiance. The results indicate that Warsaw (area: 517.2 km; population: 1 777 972) is characterized by higher light pollution than Fukuoka (area: 343.5 km; population: 1 554 229). Skyglow is primarily influenced by the number of light sources; however, local differentiation of the phenomenon depends on the spectral characteristics and design of lighting fixtures. Moreover, environmental features may affect light pollution through scattering, reflection and absorption. Outdoor lighting in Warsaw was characterized by a higher value of light illumination and greater stimulation of photoreceptors sensitive to long and medium waves. However, the lighting infrastructure in Fukuoka was also unsuitable, as it was characterised by high values of colour temperature and stimulation of photoreceptors sensitive to short waves and ganglion cells, which may be detrimental to the human body.