Search

The radiance of nighttime artificial lights measured by the VIIRS-DNB instrument on board the satellite Suomi-NPP increases at an average rate ~2.2 %/yr worldwide, whereas the artificial radiance of the night sky deduced from the Globe at Night (GAN) unaided-eye observations of the number of visible stars is reported to increase at an average rate ~9.6 %/yr. The difference between these two estimates is remarkable. This raises the question of whether the diverging temporal evolution of these indicators could be due to changes in the spectral composition of outdoor artificial light, consequence of the current process of replacement of lighting technologies. This paper presents a model for evaluating the temporal rate of change of different light pollution indicators and applies it to the VIIRS-DNB vs GAN issue, based on available data. The results show that the reported difference could be explained by spectral changes alone, if the visual observations are made under scotopic adaptation in some specific transition conditions. In case of photopic adapted observers, however, reconciling these two measurement sets requires the existence of additional light sources that affect the Globe at Night observations but do not show up in the VIIRS-DNB data. The lumen emissions of these specific sources should increase at a rate 6 %/yr worlwide, adding to the estimated 3 %/yr of the remaining lights deduced from the VIIRS-DNB measurements corrected for spectral shift., Comment: 17 pages, 1 figure. Submitted for publication

The GAia Map of the Brightness Of the Natural Sky (GAMBONS) is a model to map the natural night brightness of the sky in cloudless and moonless nights. It computes the star radiance from the photometric data in Gaia and Hipparcos catalogues, adding the contributions of the diffuse galactic and extragalactic light, zodiacal light and airglow, and taking into account the effects of atmospheric attenuation and scattering. The model allows computing the natural sky brightness in any given photometric band for a ground-based observer, if appropriate transformations from the Gaia bands are available. In this work we present the most recent improvements of the model, including the use of Gaia EDR3 data, the inclusion of a wide set of photometric bands and the derivation of additional sky brightness indicators, as the horizontal irradiance and the average hemispheric radiance, Comment: 12 pages, 3 figures

Monitoring the evolution of the anthropogenic light emissions is a priority task in light pollution research. Among the complementary approaches that can be adopted to achieve this goal stand out those based on measuring the direct radiance of the sources at ground level or from low Earth orbit satellites, and on measuring the scattered radiance (known as artificial night sky brightness or skyglow) using networks of ground-based sensors. The terrestrial atmosphere is a variable medium interposed between the sources and the measuring instruments, and the fluctuation of its optical parameters sets a lower limit for the actual source emission changes that can be confidently detected. In this paper we analyze the effect of the fluctuations of the molecular and aerosol optical depths. It is shown that for reliably detecting changes in the anthropogenic light emissions of order ~1% per year, the inter-annual variability of the annual means of these atmospheric parameters in the measurement datasets must be carefully controlled or efficiently corrected for., Comment: 20 pages, 2 figures

Light pollution is the alteration of the natural levels of darkness by an increased concentration of light particles in the nighttime environment, resulting from human activity. Light pollution is changing in a deep way the environmental conditions of the night in wide areas of the planet, and is a relevant stressor whose effects on life are being unveiled by a compelling body of research. In this paper we briefly review the basic aspects of artificial light at night as a pollutant, describing its character, magnitude and extent, its worldwide distribution, its temporal and spectral change trends, as well as its dependence on current light production technologies and prevailing social uses of light. It is shown that the overall effects of light pollution are not restricted to local disturbances, but give rise to a global, multiscale disruption of the nighttime environment., Comment: 10 pages, 1 figure. Author accepted version of a paper published in Phil. Trans. R. Soc. B

Wind farm lights are a conspicuous feature in the nocturnal landscape. Their presence is a source of light pollution for residents and the environment, severely disrupting in some places the aesthetic, cultural, and scientific values of the pristine starry skies. In this work we present a simple model for quantifying the visual impact of individual wind turbine lights, based on the comparison of their brightnesses with the brightness of well-known night sky objects. The model includes atmospheric and visual variables, and for typical parameters it shows that medium-intensity turbine lights can be brighter than Venus up to ~4 km from the turbine, brighter than alpha CMa (the brightest star on the nighttime sky) until about ~10 km, and reach the standard stellar visibility limit for the unaided eye (m_v=+6.00) at ~38 km. These results suggest that the visual range of wind farms at nighttime may be significantly larger than at daytime, a factor that should be taken into account in environmental impact assessments., Comment: 15 pages, 3 figures

The horizontal irradiance at the sea surface is an informative light pollution indicator to study Artificial Light at Night (ALAN) effects on marine biodiversity (e.g.: zooplankton diel vertical migration). The Posch ratio (PR) for the horizontal irradiance (that is, the ratio of the horizontal irradiance to the zenith radiance) is a useful tool for estimating the irradiance from easily available measurements of the zenith night sky brightness. The PR definition has already been generalized for any pair of linear radiance indicators in any pair of arbitrarily chosen photometric bands, and can also be applied to estimate e.g. the average sky radiance or the radiance at some elevation above the horizon as a function of the radiance in any other direction of the sky. The PR for a single light source depends on the distance from the source, its angular and spectral emission pattern, and the state of the atmosphere. The PR for any set of sources is a linear combination of the individual PRs that each one would produce separately, with weights that can be easily derived from the relative contribution of each source to the zenith radiance. Whereas in populated lands the ALAN PR varies relatively fast from one location to another, due to the particular spatial distribution of lights, in coastal waters and the high seas the light pollution PR is a smooth function of the distance to the shoreline, due to the progressive lack of neighboring sources and the absence of obstacles. In this work we present the fundamental equations of the model and an example of application for the waters surrounding the Iberian Peninsula, North Africa and the West Mediterranean islands., Comment: 14 pages, 5 figures, 1 table

Unfettered access to dark night skies is rapidly diminishing, due to light pollution and satellite mega-constellations tracks. Scientists should wake up and do more to stand up to Big Light and Big Space and preserve this natural resource., Comment: 5 pages; not edited version of the manuscript published in Nature Astronomy

Artificial light at night is a pollutant that is rising fast, as demonstrated by Kyba et al. (1) work by analyzing ten of thousands observations by citizen scientists in the last 12 years. The study found that the dimmest stars are vanishing, progressively hidden by a 10 percent yearly increase of the sky background due to artificial lights. This increase is difficult to be detected by the global coverage satellites now in operation, due to detector's blindness to the blue peak of white LEDs that are progressively replacing older technology lamps. This shows the need for a satellite with nighttime multi band capability in the visible light to study and control future evolution. More importantly, a call for a strong reverse in the light pollution rising trend is extremely urgent to avoid all the cultural, scientific, energetic, ecological and health negative effects of artificial nightlights., Comment: 2 pages, not edited version of the article published in Science

The rising population of artificial satellites and associated debris in low-altitude orbits is increasing the overall brightness of the night sky, threatening ground-based astronomy as well as a diversity of stakeholders and ecosystems reliant on dark skies. We present calculations of the potentially large rise in global sky brightness from space objects, including qualitative and quantitative assessments of how professional astronomy may be affected. Debris proliferation is of special concern: since all log-decades in debris size contribute approximately the same amount of night sky radiance, debris-generating events are expected to lead to a rapid rise in night sky brightness along with serious collision risks for satellites from centimetre-sized objects. This will lead to loss of astronomical data and diminish opportunities for ground-based discoveries as faint astrophysical signals become increasingly lost in the noise. Lastly, we discuss the broader consequences of brighter skies for a range of sky constituencies, equity/inclusion and accessibility for Earth- and space-based science, and cultural sky traditions. Space and dark skies represent an intangible heritage that deserves intentional preservation and safeguarding for future generations., Comment: 22 pages, 2 figures, 1 table; accepted for publication by Nature Astronomy

Contrary to some widespread intuitive belief, the night sky brightness perceived by the human eye or any other physical detector does not come (exclusively) from high in the sky. The detected brightness is built up from the scattered radiance contributed by all elementary atmospheric volumes along the line of sight, starting from the very first millimeter from the eye cornea or the entrance aperture of the measuring instrument. In artificially lit environments, nearby light sources may be responsible for a large share of the total perceived sky radiance. We present in this paper a quantitative analytical model for the sky radiance in the vicinity of outdoor light sources, free from singularities at the origin, which provides useful insights for the correct design or urban dark sky places. It is found that the artificial zenith sky brightness produced by a small ground-level source detected by a ground-level observer at short distances (from the typical dimension of the source up to several hundred meters) decays with the inverse of the distance to the source. This amounts to a reduction of 2.5 mag/arcsec2 in sky brightness for every log10 unit increase of the distance. The effects of screening by obstacles are also discussed., Comment: 35 pages, 10 figures. This is the accepted version of a manuscript whose version of record is published in Journal of Quantitative Spectroscopy & Radiative Transfer 296 (2023), 108456

The visual perception of the natural night sky in many places of the world is strongly disturbed by anthropogenic light. Part of this artificial light is scattered in the atmosphere and propagates towards the observer, adding to the natural brightness and producing a light polluted sky. However, atmospheric scattering is not the only mechanism contributing to increase the visual skyglow. The rich and diverse biological media forming the human eye also scatter light very efficiently and contribute, in some cases to a big extent, to the total sky brightness detected by the retinal photoreceptors. In this paper we quantify this effect and assess its relevance when the eye pupil is illuminated by light sources within the visual field. Our results show that intraocular scattering constitutes a significant part of the perceived sky brightness at short distances from streetlights. These results provide quantitative support to the everyday experience that substantial gains in naked-eye star limiting magnitudes can be achieved by blocking the direct light from the lamps that reaches the eye pupil. Urban lighting designs that reduce the illuminance over the eye pupil and locate the sources at large angles with respect to the visual axis are expected to help decreasing the artificial intraocular skyglow., Comment: 9 pages, 5 figures. Accepted version of a paper to be published in International Journal of Sustainable Lighting

Light pollution can be rigorously described in terms of the volume concentration of anthropogenic photons (light quanta) in the terrestrial atmosphere. This formulation, consistent with the basic physics of the emission, scattering and absorption of light, allows one to express light pollution levels in terms of particle volume concentrations, in a completely analogous way as it is currently done with other classical pollutants, like particulate matter or molecular contaminants. In this work we provide the explicit conversion equations between the photon volume concentration and the traditional light photometry quantities. This equivalent description of the light pollution levels provides some relevant insights that help to identify artificial light at night as a standard pollutant. It also enables a complementary way of expressing artificial light exposures for environmental and public health research and regulatory purposes., Comment: 15 pages, 2 figures. This is an author-formatted version of the accepted manuscript whose version of record has been published in Atmospheric Pollution Research, 2022, 13(9):101541, https://doi.org/10.1016/j.apr.2022.101541

Low Earth orbit radiometers allow monitoring nighttime anthropogenic light emissions in wide areas of the planet. In this work we describe a simple model for assessing significant outdoor lighting changes at the municipality level using on-orbit measurements complemented with ground-truth information. We apply it to evaluate the transformation effected in the municipality of Ribeira (42{\deg} 33 23 N, 8{\deg} 59 32 W) in Galicia, which in 2015 reduced the amount of installed lumen in its publicly-owned outdoor lighting system from 93.2 to 28.7 Mlm. This significant cutback, with the help of additional controls, allowed to reduce from 0.768 to 0.208 Mlm/km2 the lumen emission density averaged across the territory. In combination with the VIIRS-DNB annual composite readings these data allow to estimate that the relative weight of the emissions of the public streetlight system with respect to the total emissions of light in the municipality changed from an initial value of 74.86% to 44.68% after the transformation. The effects of the sources spectral shift and the photon calibration factor on the radiance reported by the VIIRS-DNB are also evaluated., Comment: 26 pages, 4 figures. This is the accepted version of a manuscript whose version of record is published in Journal of Quantitative Spectroscopy & Radiative Transfer 295 (2023) 108405

Modeling the hemispherical night sky brightness of anthropogenic origin is a demanding computational challenge, due to the intensive calculations required to produce all-sky maps with fine angular resolution including high-order scattering effects. We present in this Letter a physically consistent, semi-analytic two-parameter model of the all-sky radiance produced by an artificial light source that encodes efficiently the spectral radiance in all directions of the sky above the observer. The two parameters of this function are derived from the state of the atmosphere, the distance to the observer, and the source's angular and spectral emission pattern. The anthropogenic all-sky radiance at any place on Earth can be easily calculated by adding up the contributions of the surrounding artificial sources, using the information available from nighttime satellite imagery and ground-truth lighting inventories. This opens the way for the elaboration of a global world map of the artificial all-sky brightness., Comment: 5 pages, 4 figures. Accepted version of a paper to be published in MNRAS Letters (2022)

Estimating the horizontal irradiance from measurements of the zenith night sky radiance is a useful operation for basic and applied studies in observatory site assessment, atmospheric optics and environmental sciences. The ratio between these two quantities, also known as Posch ratio, has been previously studied for some canonical cases and reported for a few observational sites. In this work we (a) generalize the Posch ratio concept, extending it to any pair of radiance-related linear indicators, (b) describe its main algebraic properties, and (c) provide analytical expressions and numerical evaluations for its three basic nighttime components (moonlight, starlight and other astrophysical light sources, and artificial light). We show that the horizontal irradiance (or any other linear radiance indicator) is generally correlated with the zenith radiance, enabling its estimation from zenith measurements if some a priori information on the atmospheric state is available., Comment: 23 pages, 5 figures. This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record will be available online at doi:10.1093/mnras/stac410

Could we enjoy starry skies in our cities again? Arguably yes. The actual number of visible stars will depend, among other factors, on the spatial density of the overall city light emissions. In this paper it is shown that reasonably dark skies could be achieved in urban settings, even at the center of large metropolitan areas, if the light emissions are kept within admissible levels and direct glare from the light sources is avoided. These results may support the adoption of science-informed, democratic public decisions on the use of light in our municipalities, with the goal of recovering the possibility of contemplating the night sky everywhere in our planet., Comment: Twelve pages, five figures. Author formatted version of a paper accepted for publication in International Journal of Sustainable Lighting (2021)

Although a catalogue of synthetic RGB magnitudes, providing photometric data for a sample of 1346 bright stars, has been recently published, its usefulness is still limited due to the small number of reference stars available, considering that they are distributed throughout the whole celestial sphere, and the fact that they are restricted to Johnson V < 6.6 mag. This work presents synthetic RGB magnitudes for ~15 million stars brighter than Gaia G = 18 mag, making use of a calibration between the RGB magnitudes of the reference bright star sample and the corresponding high quality photometric G, G_BP and G_RP magnitudes provided by the Gaia EDR3. The calibration has been restricted to stars exhibiting -0.5 < G_BP - G_RP < 2.0 mag, and aims to predict RGB magnitudes within an error interval of $\pm 0.1$ mag. Since the reference bright star sample is dominated by nearby stars with slightly undersolar metallicity, systematic variations in the predictions are expected, as modelled with the help of stellar atmosphere models. These deviations are constrained to the $\pm 0.1$ mag interval when applying the calibration only to stars scarcely affected by interstellar extinction and with metallicity compatible with the median value for the bright star sample. The large number of Gaia sources available in each region of the sky should guarantee high-quality RGB photometric calibrations., Comment: 12 pages, 9 figures, 2 tables. Accepted for publication in MNRAS

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. 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 is described to illustrate these concepts., Comment: 19 pages, 3 figures. ArXiv identifier added; otherwise identical to the previous version

The population of artificial satellites and space debris orbiting the Earth imposes non-negligible constraints on both space operations and ground-based optical and radio astronomy. The ongoing deployment of several satellite `mega-constellations' in the 2020s represents an additional threat that raises significant concerns. The expected severity of its unwanted consequences is still under study, including radio interference and information loss by satellite streaks appearing in science images. In this Letter, we report a new skyglow effect produced by space objects: increased night sky brightness caused by sunlight reflected and scattered by that large set of orbiting bodies whose direct radiance is a diffuse component when observed with the naked eye or with low angular resolution photometric instruments. According to our preliminary estimates, the zenith luminance of this additional light pollution source may have already reached $\sim$20 $\mu$cd m$^{-2}$, which amounts to an approximately 10 percent increase over the brightness of the night sky determined by natural sources of light. This is the critical limit adopted in 1979 by the International Astronomical Union for the light pollution level not to be exceeded at the sites of astronomical observatories., Comment: Accepted for publication in MNRAS-L, with minor corrections. 6 pages, 4 figures

Although the use of RGB photometry has exploded in the last decades due to the advent of high-quality and inexpensive digital cameras equipped with Bayer-like color filter systems, there is surprisingly no catalogue of bright stars that can be used for calibration purposes. Since due to their excessive brightness, accurate enough spectrophotometric measurements of bright stars typically cannot be performed with modern large telescopes, we have employed historical 13-color medium-narrow-band photometric data, gathered with quite reliable photomultipliers, to fit the spectrum of 1346 bright stars using stellar atmosphere models. This not only constitutes a useful compilation of bright spectrophotometric standards well spread in the celestial sphere, the UCM library of spectrophotometric spectra, but allows the generation of a catalogue of reference RGB magnitudes, with typical random uncertainties $\sim 0.01$ mag. For that purpose, we have defined a new set of spectral sensitivity curves, computed as the median of 28 sets of empirical sensitivity curves from the literature, that can be used to establish a standard RGB photometric system. Conversions between RGB magnitudes computed with any of these sets of empirical RGB curves and those determined with the new standard photometric system are provided. Even though particular RGB measurements from single cameras are not expected to provide extremely accurate photometric data, the repeatability and multiplicity of observations will allow access to a large amount of exploitable data in many astronomical fields, such as the detailed monitoring of light pollution and its impact on the night sky brightness, or the study of meteors, solar system bodies, variable stars, and transient objects. In addition, the RGB magnitudes presented here make the sky an accessible and free laboratory for the calibration of the cameras themselves., Comment: 19 pages, 18 figures, 7 tables. Accepted for publication in MNRAS

The natural night sky brightness is a relevant input for monitoring the light pollution evolution at observatory sites, by subtracting it from the overall sky brightness determined by direct measurements. It is also instrumental for assessing the expected darkness of the pristine night skies. The natural brightness of the night sky is determined by the sum of the spectral radiances coming from astrophysical sources, including zodiacal light, and the atmospheric airglow. The resulting radiance is modified by absorption and scattering before it reaches the observer. Therefore, the natural night sky brightness is a function of the location, time and atmospheric conditions. We present in this work GAMBONS (GAia Map of the Brightness Of the Natural Sky), a model to map the natural night brightness of the sky in cloudless and moonless nights. Unlike previous maps, GAMBONS is based on the extra-atmospheric star radiance obtained from the Gaia catalogue. The Gaia-DR2 archive compiles astrometric and photometric information for more than 1.6 billion stars up to G = 21 magnitude. For the brightest stars, not included in Gaia-DR2, we have used the Hipparcos catalogue instead. After adding up to the star radiance the contributions of the diffuse galactic and extragalactic light, zodiacal light and airglow, and taking into account the effects of atmospheric attenuation and scattering, the radiance detected by ground-based observers can be estimated. This methodology can be applied to any photometric band, if appropriate transformations from the Gaia bands are available. In particular, we present the expected sky brightness for V (Johnson), and visual photopic and scotopic passbands., Comment: To be published in MNRAS. 15 pages; 13 figures. The model is available at http://gambons.fqa.ub.edu

Long-term monitoring of the evolution of the artificial night sky brightness is a key tool for developing science-informed public policies and assessing the efficacy of light pollution mitigation measures. Detecting the underlying artificial brightness trend is a challenging task, since the typical night sky brightness signal shows a large variability with characteristic time scales ranging from seconds to years. In order to effectively isolate the weak signature of the effect of interest, determining the potential long term drifts of the radiance sensing systems is crucial. If these drifts can be adequately characterized, the raw measurements could be easily corrected for them and transformed to a consistent scale. In this short note we report on the progressive darkening of the signal recorded by SQM detectors belonging to several monitoring networks, permanently installed outdoors for periods ranging from several months to several years. The sensitivity drifts were estimated by means of parallel measurements made at the beginning and at the end of the evaluation periods using reference detectors of the same kind that were little or no exposed to weathering in the intervening time. Our preliminary results suggest that SQM detectors installed outdoors steadily increase their readings at an average rate of +0.034 magSQM/arcsec^2 per MWh/m^2 of exposure to solar horizontal global irradiation, that for our locations translates into approximately +0.05 to +0.06 magSQM/arcsec^2 per year., Comment: 5 pages, 1 figure. ArXiv identifier added, some minor misprints corrected

Nighttime monitoring of the aerosol content of the lower atmosphere is a challenging task, because appropriate reference natural light sources are lacking. Here we show that the anthropogenic night sky brightness due to city lights can be successfully used for estimating the aerosol optical depth of arbitrarily thick atmospheric layers. This method requires measuring the zenith night sky brightness with two detectors located at the limiting layer altitudes. Combined with an estimate of the overall atmospheric optical depth (available from ground-based measurements or specific satellite products), the ratio of these radiances provides a direct estimate of the differential aerosol optical depth of the air column between these two altitudes. These measurements can be made with single-channel low-cost radiance detectors widely used by the light pollution research community., Comment: 5 1/2 pages, 3 figures. Accepted for publication (2020 November 03) in Monthly Notices of the Royal Astronomical Society Letters

The sustained increase of emissions of artificial light is causing a progressive brightening of the night sky in most of the world. This process represents a threat for the long-term sustainability of the scientific and educational activity of ground-based astronomical observatories operating in the optical range. Huge investments in building, scientific and technical workforce, equipment and maintenance can be at risk if the increasing light pollution levels hinder the capability of carrying out the top-level scientific observations for which these key scientific infrastructures were built. In addition, light pollution has other negative consequences, as e.g. biodiversity endangering and the loss of the starry sky for recreational, touristic, and cultural enjoyment. The traditional light pollution mitigation approach is based on imposing conditions on the photometry of individual sources, but the aggregated effects of all sources in the territory surrounding the observatories are seldom addressed in the regulations. We propose that this approach shall be complemented with a top-down, inmission limits strategy, whereby clear limits are established to the admissible deterioration of the night sky above the observatories. We describe the general form of the indicators that can be employed to this end, and develop linear models relating their values to the artificial emissions across the territory. This approach can be extended to take into account for other protection needs, and it is expected to be useful for making informed decisions on public lighting, in the context of wider spatial planning projects., Comment: arXiv identifier added. 12 pages, 2 figures

A demanding challenge in atmospheric research is the night-time characterization of aerosols using passive techniques, that is, by extracting information from scattered light that has not been emitted by the observer. Satellite observations of artificial night-time lights have been used to retrieve some basic integral parameters, like the aerosol optical depth. However, a thorough analysis of the scattering processes allows one to obtain substantially more detailed information on aerosol properties. In this Letter we demonstrate a practicable approach for determining the aerosol particle size number distribution function in the air column, based on the measurement of the angular radiance distribution of the scattered light emitted by night-time lights of cities and towns, recorded from low Earth orbit. The method is self-calibrating and does not require the knowledge of the absolute city emissions. The input radiance data are readily available from several spaceborne platforms, like the VIIRS-DNB radiometer onboard the Suomi-NPP satellite., Comment: Author prepared version of a manuscript accepted for publication in Monthly Notices of the Royal Astronomical Society (Letter) 5 pages, 5 figures

The visual brightness of the night sky is not a single-valued function of its brightness in other photometric bands, because the transformations between photometric systems depend on the spectral power distribution of the skyglow. We analyze the transformation between the night sky brightness in the Johnson-Cousins V band (mV, measured in magnitudes per square arcsecond, mpsas) and its visual luminance (L, in SI units cd m^-2) for observers with photopic and scotopic adaptation, in terms of the spectral power distribution of the incident light. We calculate the zero-point luminances for a set of skyglow spectra recorded at different places in the world, including strongly light-polluted locations and sites with nearly pristine natural dark skies. The photopic skyglow luminance corresponding to mV=0.00 mpsas is found to vary between 1.11-1.34 x 10^5 cd m^-2 if mV is reported in the absolute (AB) magnitude scale, and between 1.18-1.43 x 10^5 cd m^-2 if a Vega scale for mV is used instead. The photopic luminance for mV=22.0 mpsas is correspondingly comprised between 176 and 213 microcd m^-2 (AB), or 187 and 227 microcd m^-2 (Vega). These constants tend to decrease for increasing correlated color temperatures (CCT). The photopic zero-point luminances are generally higher than the ones expected for blackbody radiation of comparable CCT. The scotopic-to-photopic luminance ratio (S/P) for our spectral dataset varies from 0.8 to 2.5. Under scotopic adaptation the dependence of the zero-point luminances with the CCT, and their values relative to blackbody radiation, are reversed with respect to photopic ones., Comment: Version accepted for publication in Monthly Notices of the Royal Astronomical Society (2020). 5 figures, 1 table, 17 pages. Some misprints corrected in the web abstract

Determining the all-sky radiance distribution produced by artificial light sources is a computationally demanding task that generally requires an intensive calculation load. We develop in this work an analytic formulation that provides the all-sky radiance distribution produced by an artificial light source as an explicit and analytic function of the observation direction, depending on two single parameters that characterize the overall effects of the atmosphere. One of these parameters is related to the effective attenuation of the light beams, whereas the other accounts for the overall asymmetry of the combined scattering processes in molecules and aerosols. By means of this formulation a wide range of all-sky radiance distributions can be efficiently and accurately calculated in a short time. This substantial reduction in the number of required parameters, in comparison with other currently used approaches, is expected to facilitate the development of new applications in the field of light pollution research., Comment: Author formatted text of the accepted version of the paper published in Monthly Notices of the Royal Astronomical Society (2019). ArXiv id added

Several light pollution indicators are commonly used to monitor the effects of the transition from outdoor lighting systems based on traditional gas-discharge lamps to solid-state light sources. In this work we analyze a subset of these indicators, including the artificial zenithal night sky brightness in the visual photopic and scotopic bands, the brightness in the specific photometric band of the widely used Sky Quality Meter (SQM), and the top-of-atmosphere radiance detected by the VIIRS-DNB radiometer onboard the satellite Suomi-NPP. Using a single-scattering approximation in a layered atmosphere we quantitatively show that, depending on the transition scenarios, these indicators may show different, even opposite behaviors. This is mainly due to the combined effects of the changes in the sources' spectra and angular radiation patterns, the wavelength-dependent atmospheric propagation processes and the differences in the detector spectral sensitivity bands. It is suggested that the possible presence of this differential behavior should be taken into account when evaluating light pollution indicator datasets for assessing the outcomes of public policy decisions regarding the upgrading of outdoor lighting systems., Comment: 28 pages, 7 fig

Light pollution poses a growing threat to optical astronomy, in addition to its detrimental impacts on the natural environment, the intangible heritage of humankind related to the contemplation of the starry sky and, potentially, on human health. The computation of maps showing the spatial distribution of several light pollution related functions (e.g. the anthropogenic zenithal night sky brightness, or the average brightness of the celestial hemisphere) is a key tool for light pollution monitoring and control, providing the scientific rationale for the adoption of informed decisions on public lighting and astronomical site preservation. The calculation of such maps from satellite radiance data for wide regions of the planet with sub-kilometric spatial resolution often implies a huge amount of basic pixel operations, requiring in many cases extremely large computation times. In this paper we show that, using adequate geographical projections, a wide set of light pollution map calculations can be reframed in terms of two-dimensional convolutions that can be easily evaluated using conventional fast Fourier-transform (FFT) algorithms, with typical computation times smaller than 10^-6 s per output pixel., Comment: Author formatted text of the accepted version of the paper published in Journal of Quantitative Spectroscopy & Radiative Transfer 240 (2020) 106658

The light pollution levels experienced at any given site generally depend on a wide number of artificial light sources distributed throughout the surrounding territory. Since photons can travel long distances before being scattered by the atmosphere, any effective proposal for reducing local light pollution levels needs an accurate assessment of the relative weight of all intervening light sources, including those located tens or even hundreds of km away. In this paper we describe several ways of quantifying and visualizing these relative weights. Particular emphasis is made on the aggregate contribution of the municipalities, which are -- in many regions of the world -- the administrative bodies primarily responsible for the planning and maintenance of public outdoor lighting systems., Comment: Published version

Artificial light at night is a relevant environmental stressor whose unwanted consequences have been documented by a growing body of research. In this work we analize the loss of the natural darkness of the night in aquaculture farms located in shallow waters close to the shoreline, in the Atlantic coast of Galicia. High-luminance LED lampposts are switched-on the whole night long for surveillance purposes, significantly increasing the light levels throughout the whole water column, from the surface to the seabed. Measured in terms of the weighted radiance associated with the significant magnitude m1/3, the zenithal brightness at these locations is 125 times higher than should correspond to a pristine natural site. Given the potential severity of the environmental effects of artificial light at night, the dubious efficacy of light per se as a theft deterrence factor, and the availability of more efficient and environmentally friendly technologies for surveillance, the use of permanent floodlight sources in coastal areas is strongly discouraged and should be restricted as much as possible., Comment: ArXiv number added, otherwise identical to version 1

The formal link between magnitudes per square arcsecond and luminance is discussed in this paper. Directly related to the human visual system, luminance is defined in terms of the spectral radiance of the source, weighted by the CIE V($\lambda$) luminous efficiency function, and scaled by the 683 lm/W luminous efficacy constant. In consequence, any exact and spectrum-independent relationship between luminance and magnitudes per square arcsecond requires that the latter be measured precisely in the CIE V($\lambda$) band. The luminance value corresponding to m_VC=0 (zero-point of the CIE V($\lambda$) magnitude scale) depends on the reference source chosen for the definition of the magnitude system. Using absolute AB magnitudes, the zero-point luminance of the CIE V($\lambda$) photometric band is 10.96 x 10^4 cd/m^2., Comment: Accepted version, to be published in International Journal of Sustainable Lighting, www.lightingjournal.org

Under stable atmospheric conditions, the zenithal brightness of the urban sky varies throughout the night following the time course of the anthropogenic emissions of light. Different types of artificial light sources (e.g. streetlights, residential, and vehicle lights) present specific time signatures, and this feature makes it possible to estimate the amount of sky brightness contributed by each one of them. Our approach is based on transforming the time representation of the zenithal sky brightness into a modal coefficients one, in terms of the time course signatures of the sources. The modal coefficients, and hence the absolute and relative contributions of each type of source, can be estimated from the measured brightness by means of linear least squares fits. A method for determining the time signatures is described, based on wide-field time-lapse photometry of the urban nightscape. Our preliminary results suggest that artificial light leaking out of the windows of residential buildings may account for a significant share of the time-varying part of the zenithal sky brightness, whilst the contribution of the vehicle lights seems to be significantly smaller., Comment: ArXiv identifier added; acknowledgments updated

A recurring question arises when trying to characterize, by means of measurements or theoretical calculations, the zenithal night sky brightness throughout a large territory: how many samples per square kilometer are needed? The optimum sampling distance should allow reconstructing, with sufficient accuracy, the continuous zenithal brightness map across the whole region, whilst at the same time avoiding unnecessary and redundant oversampling. This paper attempts to provide some tentative answers to this issue, using two complementary tools: the luminance structure function and the Nyquist-Shannon spatial sampling theorem. The anaysis of several regions of the world, based on the data from the New world atlas of artificial night sky brightness (Falchi et al 2016, Sci. Adv. 2, e1600377) suggests that, as a rule of thumb, about one measurement per square kilometer could be sufficient for determining the zenithal night sky brightness of artificial origin at any point in a region to within 0.1 magV/arcsec2 (in the root-mean-square sense) of its true value in the Johnson-Cousins V band. The exact reconstruction of the zenithal night sky brightness maps from samples taken at the Nyquist rate seems to be considerably more demanding., Comment: Accepted version, Monthly Notices of the Royal Astronomical Society

Light pollution is a worldwide phenomenon whose consequences for the natural environment and the human health are being intensively studied nowadays. Most published studies address issues related to light pollution inland. Coastal waters, however, are spaces of high environmental interest, due to their biodiversity richness and their economical significance. The elevated population density in coastal regions is accompanied by correspondingly large emissions of artificial light at night, whose role as an environmental stressor is increasingly being recognized. (...) At the same time, the marine surface environment provides a stage free from obstacles for measuring the dependence of the skyglow on the distance to the light polluting sources, and validating (or rejecting) atmospheric light propagation models. In this work we present a proof-of-concept of a gimbal measurement system that can be used for zenithal skyglow measurements on board both small boats and large vessels under actual navigation conditions. We report the results obtained in the summer of 2016 along two measurement routes in the Mediterranean waters offshore Barcelona, travelling 9 and 31.7 km away from the coast. The atmospheric conditions in both routes were different from the ones assumed for the calculation of recently published models of the anthropogenic sky brightness. They were closer in the first route, whose results approach better the theoretical predictions. The results obtained in the second route, conducted under a clearer atmosphere, showed systematic differences that can be traced back to two expected phenomena, which are a consequence of the smaller aerosol content: the reduction of the anthropogenic sky glow at short distances from the sources, and the slower decay rate of brightness with distance, which gives rise to a relative excess of brightness at large distances from the coastline., Comment: Accepted version

Light plays a key role in the regulation of different physiological processes, through several visual and non-visual retinal phototransduction channels whose basic features are being unveiled by recent research. The growing body of evidence on the significance of these effects has sparked a renewed interest in the determination of the light field at the entrance pupil of the eye in indoor spaces. Since photic interactions are strongly wavelength-dependent, a significant effort is being devoted to assess the relative merits of the spectra of the different types of light sources available for use at home and in the workplace. The spectral content of the light reaching the observer eyes in indoor spaces, however, does not depend exclusively on the sources: it is partially modulated by the spectral reflectance of the walls and surrounding surfaces, through the multiple reflections of the light beams along all possible paths from the source to the observer. This modulation can modify significantly the non-visual photic inputs that would be produced by the lamps alone, and opens the way for controlling -to a certain extent- the subject's exposure to different regions of the optical spectrum. In this work we evaluate the expected magnitude of this effect and we show that, for factorizable sources, the spectral modulation can be conveniently described in terms of a set of effective filter-like functions that provide useful insights for lighting design and light pollution assessment. The radiance field also provides a suitable bridge between indoor and outdoor light pollution studies., Comment: Accepted version, to be published in Journal of Quantitative Spectroscopy & Radiative Transfer