Optimizing lighting of rural roads and protected areas with white light: a compromise among light pollution, energy savings, and visibility

Abstract

The broad implementation of light emitting diode (LED) light sources in public lighting has become a revolution in recent years. Their low power consumption and good performance (extremely low onset time, long lifetime, high efficacy) make LEDs an optimal solution in most outdoor applications. In addition, the white light emitted by the vast majority of LEDs used in public lighting and their good color rendering improve well-being, comfort, and safety in cities, especially in commercial zones and urban centers. However, regulations on light pollution that have been developed in some countries in parallel to the introduction of LED lighting impose strong constraints to white light emission, which is present due to the higher Rayleigh scattering of short wavelengths. These regulations request filtering blue wavelengths in some protected areas and thus limit the projects to high- or low-pressure sodium sources or amber LEDs. In this work, the pros and cons of white and amber LED lighting in rural areas are analyzed and compared through simulations made on a typical rural lighting situation and considerations based on efficiency, visual performance, nonvisual effects, and light pollution. The most important conclusion is that Rayleigh scattering seems to prevail in the current considerations on light pollution, whereas other important aspects affecting safety and sustainability are are not considered. Accurate designs can decrease light pollution without constraints against white LEDs. The objective of this work is to provide evidence leading to consider light pollution from a more general perspective in the benefit of humans and the environment.