Generalizing the world atlas of artificial night sky brightness to encompass a wide range of sky states

Abstract

We propose here a method to extend future global maps of light pollution beyond the usual description based on clear sky conditions. For this purpose we describe the use of a cloud-fraction conversion factor to be used in combination with the usual light pollution propagation functions for clean atmosphere. This allows to show the influence of different cloud coverage fraction on, e.g. zenith radiance, average radiance in the night sky hemisphere, horizontal irradiance, and other light pollution indicators. This will help describing light pollution levels when clouds alter the radiance of the night sky, giving astronomers an additional way to evaluate the quality of the sky at observatories' sites for a consistent fraction of the nights when observations are made in not photometric nights. The knowledge of the artificial sky radiance in different cloud conditions is also fundamental for studying the ecological consequences of artificial light at night and for helping determining the levels of pollution in sites (e.g. natural reserves and parks, suburban locations, city centres). This will also help to control if the eventually enforced light pollution indicators limits are surpassed or not and, in case, to make plans to re-enter into the agreed limits.