CA : A Cancer Journal for Clinicians

Artificial lights raise night sky luminance, creating the most visible effect of light pollution—artificial skyglow. Despite the increasing interest among scientists in fields such as ecology, astronomy, health care, and land-use planning, light pollution lacks a current quantification of its magnitude on a global scale. To overcome this, we present the world atlas of artificial sky luminance, computed with our light pollution propagation software using new high-resolution satellite data and new precision sky brightness measurements. This atlas shows that more than 80% of the world and more than 99% of the U.S. and European populations live under light-polluted skies. The Milky Way is hidden from more than one-third of humanity, including 60% of Europeans and nearly 80% of North Americans. Moreover, 23% of the world’s land surfaces between 75°N and 60°S, 88% of Europe, and almost half of the United States experience light-polluted nights.

The new world atlas of artificial night sky brightness.

Light absorption by aerosols contributes to solar radiative forcing through absorption of solar radiation and heating of the absorbing aerosol layer. Besides the direct radiative effect, the heating can evaporate clouds and change the atmospheric dynamics. Aerosol light absorption in the atmosphere is dominated by black carbon (BC) with additional, significant contributions from the still poorly understood brown carbon and from mineral dust. Sources of these absorbing aerosols include biomass burning and other combustion processes and dust entrainment. For particles much smaller than the wavelength of incident light, absorption is proportional to the particle volume and mass. Absorption can be calculated with Mie theory for spherical particles and with more complicated numerical methods for other particle shapes. The quantitative measurement of aerosol light absorption is still a challenge. Simple, commonly used filter measurements are prone to measurement artifacts due to particle concentration and modification of particle and filter morphology upon particle deposition, optical interaction of deposited particles and filter medium, and poor angular integration of light scattered by deposited particles. In situ methods measure particle absorption with the particles in their natural suspended state and therefore are not prone to effects related to particle deposition and concentration on filters. Photoacoustic and refractive index-based measurements rely on the heating of particles during light absorption, which, for power-modulated light sources, causes an acoustic signal and modulation of the refractive index in the air surrounding the particles that can be quantified with a microphone and an interferometer, respectively. These methods may suffer from some interference due to light-induced particle evaporation. Laser-induced incandescence also monitors particle heating upon absorption, but heats absorbing particles to much higher temperatures to quantify BC mass from the thermal radiation emitted by the heated particles. Extinction-minus-scattering techniques have limited sensitivity for measuring aerosol light absorption unless the very long absorption paths of cavity ring-down techniques are used. Systematic errors can be dominated by truncation errors in the scattering measurement for large particles or by subtraction errors for high single scattering albedo particles. Remote sensing techniques are essential for global monitoring of aerosol light absorption. While local column-integrated measurements of aerosol light absorption with sun and sky radiometers are routinely done, global satellite measurements are so far largely limited to determining a semi-quantitative UV absorption index.

Aerosol light absorption and its measurement: A review

The energy delivery of a solar-energy system is generally associated with the sun's available irradiance and spectral content, as well as a variety of environmental and climatic factors and inherent system and component performances. However, other external factors relating to geographical location and conditions can have even greater impacts on system performance. Among these, soiling is a commonly overlooked or underestimated issue that can be a showstopper for the viability of a solar installation. This paper provides a comprehensive overview of soiling problems, primarily those associated with “dust” (sand) and combined dust–moisture conditions that are inherent to many of the most solar-rich geographic locations worldwide. We review and evaluate key contributions to the understanding, performance effects, and mitigation of these problems. These contributions span a technical history of almost seven decades. We also present an inclusive literature survey/assessment. The focus is on both transmissive surfaces (e.g., those used for flat-plate photovoltaics or for concentrating lenses) and reflective surfaces (e.g., mirrors or heliostats for concentrating power systems).

A comprehensive review of the impact of dust on the use of solar energy: History, investigations, results, literature, and mitigation approaches

The solution of electromagnetic scattering by a homogeneous prolate (or oblate) spheroidal particle with an arbitrary size and refractive index is obtained for any angle of incidence by solving Maxwell's equations under given boundary conditions. The method used is that of separating the vector wave equations in the spheroidal coordinates and expanding them in terms of the spheroidal wavefunctions. The unknown coefficients for the expansion are determined by a system of equations derived from the boundary conditions regarding the continuity of tangential components of the electric and magnetic vectors across the surface of the spheroid. The solutions both in the prolate and oblate spheroidal coordinate systems result in a same form, and the equations for the oblate spheroidal system can be obtained from those for the prolate one by replacing the prolate spheroidal wavefunctions with the oblate ones and vice versa. For an oblique incidence, the polarized incident wave is resolved into two components, the TM mode for which the magnetic vector vibrates perpendicularly to the incident plane and the TE mode for which the electric vector vibrates perpendicularly to this plane. For the incidence along the rotation axis the resultant equations are given in the form similar to the one for a sphere given by the Mie theory. The physical parameters involved are the following five quantities: the size parameter defined by the product of the semifocal distance of the spheroid and the propagation constant of the incident wave, the eccentricity, the refractive index of the spheroid relative to the surrounding medium, the incident angle between the direction of the incident wave and the rotation axis, and the angles that specify the direction of the scattered wave.

Light Scattering by a Spheroidal Particle

Artificial light at night can be harmful to the environment, and interferes with fauna and flora, star visibility, and human health. To estimate the relative impact of a lighting device, its radiant power, angular photometry and detailed spectral power distribution have to be considered. In this paper we focus on the spectral power distribution. While specific spectral characteristics can be considered harmful during the night, they can be considered advantageous during the day. As an example, while blue-rich Metal Halide lamps can be problematic for human health, star visibility and vegetation photosynthesis during the night, they can be highly appropriate during the day for plant growth and light therapy. In this paper we propose three new indices to characterize lamp spectra. These indices have been designed to allow a quick estimation of the potential impact of a lamp spectrum on melatonin suppression, photosynthesis, and star visibility. We used these new indices to compare various lighting technologies objectively. We also considered the transformation of such indices according to the propagation of light into the atmosphere as a function of distance to the observer. Among other results, we found that low pressure sodium, phosphor-converted amber light emitting diodes (LED) and LED 2700 K lamps filtered with the new Ledtech’s Equilib filter showed a lower or equivalent potential impact on melatonin suppression and star visibility in comparison to high pressure sodium lamps. Low pressure sodium, LED 5000 K-filtered and LED 2700 K-filtered lamps had a lower impact on photosynthesis than did high pressure sodium lamps. Finally, we propose these indices as new standards for the lighting industry to be used in characterizing their lighting technologies. We hope that their use will favor the design of new environmentally and health-friendly lighting technologies.

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Evaluating Potential Spectral Impacts of Various Artificial Lights on Melatonin Suppression, Photosynthesis, and Star Visibility

The scalable theoretical model of light pollution for ground sources is presented. The model is successfully employed for simulation of angular behavior of the spectral and integral sky radiance and/or luminance during nighttime. There is no restriction on the number of ground-based light sources or on the spatial distribution of these sources in the vicinity of the measuring point (i.e., both distances and azimuth angles of the light sources are configurable). The model is applicable for real finite-dimensional surface sources with defined spectral and angular radiating properties contrary to frequently used point-source approximations. The influence of the atmosphere on the transmitted radiation is formulated in terms of aerosol and molecular optical properties. Altitude and spectral reflectance of a cloud layer are the main factors introduced for simulation of cloudy and/or overcast conditions. The derived equations are translated into numerically fast code, and it is possible to repeat the entire set of calculations in real time. The parametric character of the model enables its efficient usage by illuminating engineers and/or astronomers in the study of various light-pollution situations. Some examples of numerical runs in the form of graphical results are presented.

Light-pollution model for cloudy and cloudless night skies with ground-based light sources

Effect of electromagnetic radiation scattering on homogeneous spherical dust particle which carries excess surface electric charge is investigated. Numerical calculations are presented for the cases of (i) charged spherical particles present in the interplanetary space of the Solar System, and (ii) charged water droplets and ice grains in the Earth's atmosphere. The results show that the surface charge may influence optical properties of very small particles with size parameter x less than 0.01 (astronomical materials like amorphous carbon and silicate are affected also at x ≈ 0.03 ). Slightly absorbing charged particles may attenuate the electromagnetic radiation more than 10 times efficiently than equivalent non-charged particles. The effect of temperature on efficiency factors for scattering Q sca , absorption Q abs , and radiation pressure Q pr is evaluated for astronomical amorphous carbon, as cosmic dust particles may undergo large temperature changes during their motion in the circumstellar regions. The ratios Q x charged / Q x neutral (for x = abs , ext , or pr) increase with decreasing grain temperature.

Scattering of electromagnetic waves by charged spheres and some physical consequences

This research was supported by Fonds de recherche du Quebec – Nature et technologies (FRQNT-186263) and by the Federation des Cegeps, by the Slovak Research and Development Agency under contract No. APVV-14-0017, by Spanish projects AYA2012-31277 and AYA2013-46724-P and the Spanish Network for Light Pollution Studies (AYA2015-71542-REDT) from the Spanish Ministerio de Economia y Competitividad. This research also received support from a Medzinarodna Vedecko-Technicka Spolupraca (MVTS) grant of the Slovak Academy of Sciences. This research was supported in part by the STARS4ALL project and ORISON project funded by the European Union H2020-ICT-2015-688135 and H2020-INFRASUPP-2015-2.

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Sky Quality Meter measurements in a colour-changing world

Dedication. Preface. Observational Information. In the Kitchen of Dust Modeling N.V. Voshchinnikov. Infrared Spectroscopy of Cosmic Dust G.J. Flynn, et al. Experimental Light Scattering Matrices Between to Cosmic Dust O. Munoz, et al. Light Scattering Models. Light Scattering Tools for Cosmic Dust Modeling V.B. Il'In, et al. Fractal Aggregates in Space G. Wurm, M. Schnaiter. Scattering of Light by a Sphere with an Arbitrary Radially Variable Refractive Index A.Y. Perelman, et al. Calculation of Optical Fields Inside Spheroidal Particles of Cosmic Dust: Comparison of Different Methods: GMT, T-Matrix, SVM V.A. Babenko, P.K. Petrov. Thermal Effects of Radiation on Dust Particles L.G. Astafyeva. Characterization Methodologies. Size Distributions of Particles Obtained by Inversion of Spectral Extinction and Scattering Measurements H. Horvath, et al. Simplified Solution of the Inverse Problem for Instantaneous Cometary Dust Size Distribution M. Kocifaj, et al. Monte Carlo Modeling of Cometary Atmospheres Including Polarization F. Moreno, et al. Atmospheric Extinction Derived from Cometary Observations J. Svoren, et al. Backscatter Polarization. Photometric and Polarimetric Opposition Phenomena Exhibited by Solar System Bodies V. Rosenbush, et al. Experimental Modeling of Opposition Effect and Negative Polarization of Regolith-Like Surfaces Y.G. Shkuratov, A.V. Ovcharenko. Exact Results of the Vector Theory of Coherent Backscattering from Discrete Random Media: An Overview M. Mishchenko, et al. Numerical Techniques for Backscattering by Random Media K. Muinonen, et al. Dynamics. The Effect of Radiation on the Motion of Meteoroids I.P. Williams. Covariant Equation of Motion for a Particle in an Electromagnetic Field J. Klacka. Participants. Index.

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Miroslav Kocifaj

Papers

Evaluating Potential Spectral Impacts of Various Artificial Lights on Melatonin Suppression, Photosynthesis, and Star Visibility

Light-pollution model for cloudy and cloudless night skies with ground-based light sources

Scattering of electromagnetic waves by charged spheres and some physical consequences

Sky Quality Meter measurements in a colour-changing world

Optics of cosmic dust