Light pollution in ultraviolet and visible spectrum: effect on different visual perceptions.

In general terms, lighting research has been focused in the development of artificial light with the purpose of saving energy and having more durable lamps. However, the consequences that artificial night lighting could bring to the human being and living organisms have become an important issue recently. Light pollution represents a significant problem to both the environment and human health causing a disruption of biological rhythms related not only to the visible spectrum, but also to other parts of the electromagnetic spectrum. Since the lamps emit across a wide range of the electromagnetic spectrum, all photobiological species may be exposed to another type of light pollution. By comparing five different lamps, the present study attempts to evaluate UV radiative fluxes relative to what humans and two species of insects perceive as sky glow level. We have analyzed three atmospheric situations: clear sky, overcast sky and evolving precipitable water content. One important finding suggests that when a constant illuminance of urban spaces has to be guaranteed the sky glow from the low pressure sodium lamps has the most significant effect to the visual perception of the insects tested. But having the fixed number of luminaires the situation changes and the low pressure sodium lamp would be the best choice for all three species. The sky glow effects can be interpreted correctly only if the lamp types and the required amount of scotopic luxes at the ground are taken into account simultaneously. If these two factors are combined properly, then the ecological consequences of sky glow can be partly reduced. The results of this research may be equally useful for lighting engineers, architects, biologists and researchers who are studying the effects of sky glow on humans and biodiversity

A comparison contrasting the relative spectra of the lamps and the spectral vision of the three species is shown in this figure.

<p>The main objective is to see clearly the differences between the lamp emissions and to relate them to what the species can feel.</p

The spectral sensitivity of the dark-adapted eye of alate M. persicae (an aphid species), the spectral sensitivity of Narathura bazalus (a lepidoptera species) and the scotopic spectral sensitivity of humans are considered here.

<p>The spectral sensitivity of the dark-adapted eye of alate M. persicae (an aphid species), the spectral sensitivity of Narathura bazalus (a lepidoptera species) and the scotopic spectral sensitivity of humans are considered here.</p

The legend to this figure is the same as in <b>Fig. 8</b>.

<p>The legend to this figure is the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056563#pone-0056563-g008" target="_blank"><b>Fig. 8</b></a>.</p

Characteristics and relative emissions of the five light sources.

<p>The <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056563#pone-0056563-t001" target="_blank">Tab. 1</a> can be read in different ways. For instance, if a constant radiative emission is required independent of lamp-type, then two LED lamps are needed to supply the VIS emissions by one HPS lamp. However, if the human perception is considered, one can easily recognize that LED lamp emits about 27% more than HPS lamp. In this case only 4 LED lamps are necessary to produce the luminous energy equivalent to 5 HPS lamps. Note that all these evaluations were made for direct emissions of the lamps considered and not for a diffuse radiation of a night-sky that can be detected at the ground as a diffuse irradiance .</p

Total amount of precipitable water is 0.3 atmospheric centimeters.

<p>The curve styles coincide with those that have been used in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056563#pone-0056563-g003" target="_blank">Fig. 3</a>. The results were obtained under assumption of constant luminous emission to the upper hemisphere; the computed flux densities are normalized to the visual sensitivity of the organisms selected for the present study.</p

The is the aerosol optical thickness at the reference wavelength 500 nm.

<p> One of the most interesting features of this figure is the possibility to extract the portions of sky glow levels in VIS spectral band. The aim is to evaluate the radiative fluxes based on the luminous fluxes that humans can feel as sky glow. The evaluated ratios are measured in lx.W⁻¹.m².</p

Total amount of precipitable water is 0.3 atmospheric centimeters.

<p>Two models are used to characterize clear sky conditions: no aerosol contamination (light-gray curves) and aerosol contamination characterized by optical thickness  = 0.5 at  = 500 nm (dark-gray curves). Consequently, the spectral features of sky glow under overcast sky conditions with total atmospheric optical thickness  = 7.0 are correspondingly determined (black curves).</p

Total amount of precipitable water is 0.3 atmospheric centimeters.

<p>The curve styles are the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056563#pone-0056563-g003" target="_blank">Fig. 3</a>. The results were obtained under assumption of constant number of light sources and the computed flux densities are normalized to the visual sensitivity of the organisms selected for the present study.</p

The legend to this figure is the same as in <b>Fig. 8</b>.

<p>The legend to this figure is the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056563#pone-0056563-g008" target="_blank"><b>Fig. 8</b></a>.</p