Limiting the impact of light pollution on human health, environment and stellar visibility

TL;DR

This paper analyzes the spectral emissions of various outdoor lamps, highlighting how certain types, especially white LEDs, significantly increase residual light pollution, which impacts human health, wildlife, and star visibility, and proposes criteria for regulation.

Contribution

It introduces a spectral analysis framework for evaluating lamps and provides regulatory criteria to limit residual light pollution effects.

Findings

White LEDs and metal halide lamps increase pollution in scotopic and melatonin suppression bands.

Low pressure sodium lamps are the most environmentally friendly among common outdoor lighting.

Migration to white lamps could increase light pollution by over five times in certain spectral bands.

Abstract

Light pollution is one of the most rapidly increasing types of environmental degradation. To limit this pollution several effective practices have been defined: shields on lighting fixtures to prevent direct upward light; no over lighting, i.e. avoid using higher lighting levels than strictly needed for the task, constraining illumination to the area where and when it is needed. Nevertheless, even after the best control of the light distribution is reached and when the proper quantity of light is used, upward light emission remains, due to reflections from the lit surfaces and atmospheric scatter. The environmental impact of this "residual light pollution" cannot be neglected and should be limited too. We propose a new way to limit the effects of this residual light pollution on wildlife, human health and stellar visibility. We performed analysis of the spectra of common types of lamps for external use, including the new LEDs. We evaluated their emissions relative to the spectral response functions of human eye photoreceptors, in the photopic, scotopic and melatonin suppressing bands finding that the amount of pollution is strongly dependent on the spectral characteristics of the lamps, with the more environmentally friendly lamps being low pressure sodium, followed by high pressure sodium. Most polluting are the lamps with a strong blue emission, like white LEDs. Migration from the now widely used sodium lamps to white lamps (Metal Halide and LEDs) would produce an increase of pollution in the scotopic and melatonin suppression bands of more than five times the present levels, supposing the same photopic installed flux. This increase will exacerbate known and possible unknown effects of light pollution on human health, environment and on starry sky visibility. We present quantitative criteria to evaluate the lamps based on their spectral emissions and we suggest regulatory limits.