Keeping light pollution at bay: A red-lines, target values, top-down approach

Abstract

The prevailing regulatory framework for light pollution control is based on establishing conditions on individual light sources or single installations (regarding features like ULOR, spectrum, illuminance levels, glare, …), in the hope that an ensemble of individually correct lighting installations will be effective to somehow solve this problem. This "local sources" approach is indeed necessary, and shall no doubt be enforced; however, it seems to be clearly insufficient for curbing the actual process of degradation of the night, and for effectively attaining the necessary remediation goals. In this paper we describe a complementary (not substitutive) ’red-lines’ strategy that should in our opinion be adopted as early as possible in the policies for light pollution control. It is based on setting maximum values for absolute light pollution indicators and using linear models relating the indicators to the source emissions in order to establish the maximum light emissions compatible with these red-lines. This top- down approach seeks to set definite limits on the allowable degradation of the night, providing the methodological tools required for making science-informed public policy decisions and for managing the transition processes. Light pollution abatement should routinely be included as an integral part of any territorial management plan. A practical application case-study based on the night sky brightness at zenith is described to illustrate these concepts.