Search Results (13)

We present the first dark-sky map of Thailand, derived from calibrated Visible Infrared Imaging Radiometer Suite (VIIRS) satellite data spanning 2012–2023. Artificial night-sky brightness was classified into 14 levels, with Classes 1–9 defined as potential dark-sky areas where the Milky Way remains visible. International comparisons with the United Kingdom, Chile, and Botswana reveal that Thailand has undergone the steepest decline, losing 15.4% of pristine skies since 2012, while the UK remained stable (+0.8%), Botswana nearly unchanged (−0.7%), and Chile moderately degraded (−5.3%). A correlation analysis shows strong negative associations between potential dark-sky area and both GDP ($r=-0.65$) and population ($r=-0.68$), while inflation ($r=0.26$) and unemployment ($r=0.24$) exhibit weak influence. Five algorithms, including GLM and machine learning models, were tested; among them, the Decision Tree achieved the lowest relative error ($0.4\%\pm 0.3\%$), with ensemble methods and GLM performing comparably and Deep Learning being less accurate. By 2023, over 60% of Thais lived under skies too bright to observe the Milky Way by naked eye, and one-fifth were exposed to intensities preventing dark adaptation. Thailand’s rapid transition to LED street lighting after 2015, while energy-efficient, has intensified skyglow. Protecting remaining dark-sky areas requires urgent policies, linking conservation to human health, biodiversity, cultural heritage, and sustainable development. Full article

Light pollution is a rapidly growing environmental challenge, with the global brightness of the night sky increasing by an average of 9.6% per year. This study assessed the ecological impact of artificial light at night (ALAN) on protected areas in Poland, including all 23 national and 125 landscape parks, from 2012 to 2023. Based on VIIRS satellite radiance data and modelled sky surface brightness (Sa), we developed and applied the Ecological Light Pollution (ELP) scale, which classifies areas into four classes of ecological impact: strong (ELP-A), pronounced (ELP-B), noticeable (ELP-C), and weak or none (ELP-D). The analysis revealed that 38.5% of protected areas are affected by artificial skyglow at levels classified as ELP-B or ELP-C. Under cloudy conditions, which intensify light pollution effects, 22% of national parks and 41.8% of landscape parks fell into these classes. Notably, Wielkopolski National Park exhibited the most pronounced impact (ELP-B) even under clear skies, primarily due to its proximity to the Poznań metropolitan area. In contrast, Bieszczadzki and Białowieski National Parks recorded near-natural darkness (ELP-D). These light pollution effects can disrupt nocturnal species’ behaviour, reduce biodiversity, and degrade opportunities for dark-sky tourism. The findings emphasise the need for targeted mitigation, including stricter outdoor lighting regulations, formal dark-sky protection zones, and public education to preserve protected areas’ ecological integrity and tourism potential. Full article

The data retrieved from satellite imagery and ground-based photometers are the two main sources of information on light pollution and are thus the two main tools for tackling the problem of artificial light pollution at night (ALAN). While satellite data offer high spatial coverage, on the other hand, photometric data provide information with a higher degree of temporal resolution. Thus, studying the proper correlation between both sources will allow us to calibrate and integrate them to obtain data with both high temporal resolution and spatial coverage. For this purpose, more than 15,000 satellite measurements and 400,000 measurements from 72 photometers for the year 2022 were used. The photometers used were the Sky-Glow Wireless Autonomous Sensor (SG-WAS) and Telescope Encoder and Sky Sensor WIFI (TESS-W) types, located at different ground-based locations, mainly in Spain. These photometers have a spectral sensitivity closer to that of VIIRS than to the Sky Quality Meter (SQM). In this study, a good correlation of data from the Day–Night Band (DNB) from the Visible Infrared Imaging Radiometer Suite (VIIRS) with a red photometric network between 19.41 mag/arcsec${}^2$ and 21.12 mag/arcsec${}^2$ was obtained. Full article

We provide quantitative results from GIS-based modelling of urban emission functions for a range of representative low- and mid-rise locations, ranging from individual streets to residential communities within cities, as well as entire towns and city regions. Our general aim is to determine whether lantern photometry or built environment has the dominant effect on light pollution and whether it is possible to derive a common emission function applicable to regions of similar type. We demonstrate the scalability of our work by providing results for the largest urban area modelled to date, comprising the central 117 km² area of Dublin City and containing nearly 42,000 public lights. Our results show a general similarity in the shape of the azimuthally averaged emission function for all areas examined, with differences in the angular distribution of total light output depending primarily on the nature of the lighting and, to a smaller extent, on the obscuring environment, including seasonal foliage effects. Our results are also consistent with the emission function derived from the inversion of worldwide skyglow data, supporting our general results by an independent method. Additionally, a comparison with global satellite observations shows that our results are consistent with the deduced angular emission function for other low-rise areas worldwide. Finally, we validate our approach by demonstrating very good agreement between our results and calibrated imagery taken from the International Space Station of a range of residential locations. To our knowledge, this is the first such detailed quantitative verification of light loss calculations and supports the underlying assumptions of the emission function model. Based on our findings, we conclude that it should be possible to apply our approach more generally to produce estimates of the energy and environmental impact of urban areas, which can be applied in a statistical sense. However, more accurate values will depend on the details of the particular locations and require treatment of atmospheric scattering, as well as differences in the spectral nature of the sources. Full article

The COVID-19 epidemic lockdown has a direct influence on urban socioeconomic activity, including night-time light (NTL) changes. Night-time skyglow, a form of light pollution caused by NTL, is also affected by public emergencies. Here we investigated the impact of the lockdown on the night-time skyglow in the Guangbutun region of Wuhan, China. We monitored the night-time sky from 1 November 2019 to 12 April 2020 and compared the intraday skyglow pattern and day-to-day variation of skyglow before and during the lockdown. We found that the detected earliest shutdown timing of lights (STL) was moved from 22:00 (before the lockdown) to 21:30 (after entering the lockdown), and the fluctuation of skyglow decreased significantly during the lockdown. Furthermore, we found the night-time skyglow at various time intervals generally decreased and then recovered during the lockdown. The most severe decrease in zenith sky brightness (ZSB) was observed at the 21:30–22:00 time interval, with a decrease ratio (DR) of 72.1% and a recovery ratio (RR) of only 22.6%. On the other hand, the skyglow near midnight was the least affected by the lockdown, and the RR (32.6% and 24.3%) was comparable to the DR (30.4% and 38.2%), which means the skyglow at this time basically recovered to the pre-epidemic level. We conclude that long-term monitoring of sky brightness using single-channel photometers, such as SQMs, can provide a multi-temporal microscopic perspective for studying the dynamics of skyglow caused by human activities. Full article

Sky Quality Meter (SQM) is a commercial instrument based on photometers widely used by amateur astronomers for skyglow measurement from the ground. In the framework of the MINLU project, two SQM-LE units were integrated in an autonomous sensor suite realized and tested at University of Padova for monitoring light pollution from drones or sounding balloons. During the ground tests campaign before airborne measurement, the performance of both SQM units was verified in laboratory using controlled light sources as a reference input; the results showed that both units presented an angular response deviating consistently from the expected performance and that the sensors’ field of view was larger than the one declared in the manufacturer’s datasheet. This aspect in particular would affect direct skyglow measurements during flight as light sources close to the boundaries of the field of view would not be attenuated but instead detected by the sensors. As a direct consequence, the measurement of low-intensity skyglows at stratospheric altitudes could be affected by high-intensity punctual sources acting as lateral disturbances. A dedicated test campaign was therefore conceived and realized to investigate SQM unit response to light sources in the field of view and identify the true angular response curve; the setup consisted in a controlled rotatory stage moving the unit in front of a fixed diffusive light source. Different test conditions were used to validate the experimental procedure, demonstrating the repeatability of the measurements. This paper presents the experimental campaign and the resulting SQM angular response curve; results indicate for both SQMs a larger than expected field of view and the presence of a double peak in the angular response, which is likely related to a non-perfect alignment of SQMs collimation optics. Furthermore, the wider resulting curves suggest that the contribution of lateral sources is more prominent with respect to the response predicted by the manufacturer. For this reason, the utilization of baffles to restrict SQMs field of view is analyzed to minimize the disturbance of lateral light sources and two different geometries are presented. Full article

The main features of SG-WAS (SkyGlow Wireless Autonomous Sensor), a low-cost device for measuring Night Sky Brightness (NSB), are presented. SG-WAS is based on the TSL237 sensor –like the Unihedron Sky Quality Meter (SQM) or the STARS4ALL Telescope Encoder and Sky Sensor (TESS)–, with wireless communication (LoRa, WiFi, or LTE-M) and solar-powered rechargeable batteries. Field tests have been performed on its autonomy, proving that it can go up to 20 days without direct solar irradiance and remain hibernating after that for at least 4 months, returning to operation once re-illuminated. A new approach to the acquisition of average NSB measurements and their instrumental uncertainty (of the order of thousandths of a magnitude) is presented. In addition, the results of a new Sky Integrating Sphere (SIS) method have shown the possibility of performing mass device calibration with uncertainties below 0.02 mag/arcsec${}^2$. SG-WAS is the first fully autonomous and wireless low-cost NSB sensor to be used as an independent or networked device in remote locations without any additional infrastructure. Full article

Artificial skyglow, the brightening of the night sky by artificial light at night that is scattered back to Earth within the atmosphere, is detrimental to astronomical observations and has an impact on ecosystems as a form of light pollution. In this work, we investigated the impact of the lockdown caused by the COVID-19 pandemic on the urban skyglow of Berlin, Germany. We compared night sky brightness and correlated color temperature (CCT) measurements obtained with all-sky cameras during the COVID-19 lockdown in March 2020 with data from March 2017. Under normal conditions, we expected an increase in night sky brightness (or skyglow, respectively) and CCT because of the transition to LED. This is supported by a measured CCT shift to slightly higher values and a time series analysis of night-time light satellite data showing an increase in artificial light emission in Berlin. However, contrary to this observation, we measured a decrease in artificial skyglow at zenith by 20% at the city center and by more than 50% at 58 km distance from the center during the lockdown. We assume that the main cause for the reduction of artificial skyglow originates from improved air quality due to less air and road traffic, which is supported by statistical data and satellite image analysis. To our knowledge, this is the first reported impact of COVID-19 on artificial skyglow and we conclude that air pollution should shift more into the focus of light pollution research. Full article

The disruption to natural light regimes caused by outdoor artificial nighttime lighting has significant impacts on human health and the natural world. Artificial light at night takes two forms, light emissions and skyglow (caused by the scattering of light by water, dust and gas molecules in the atmosphere). Key to determining where the biological impacts from each form are likely to be experienced is understanding their spatial occurrence, and how this varies with other landscape factors. To examine this, we used data from the Visible Infrared Imaging Radiometer Suite (VIIRS) day/night band and the World Atlas of Artificial Night Sky Brightness, to determine covariation in (a) light emissions, and (b) skyglow, with human population density, landcover, protected areas and roads in Britain. We demonstrate that, although artificial light at night increases with human density, the amount of light per person decreases with increasing urbanization (with per capita median direct emissions three times greater in rural than urban populations, and per capita median skyglow eleven times greater). There was significant variation in artificial light at night within different landcover types, emphasizing that light pollution is not a solely urban issue. Further, half of English National Parks have higher levels of skyglow than light emissions, indicating their failure to buffer biodiversity from pressures that artificial lighting poses. The higher per capita emissions in rural than urban areas provide different challenges and opportunities for mitigating the negative human health and environmental impacts of light pollution. Full article

Artificial skyglow, the fraction of artificial light at night that is emitted upwards from Earth and subsequently scattered back within the atmosphere, depends on atmospheric conditions but also on the ground albedo. One effect that has not gained much attention so far is the amplification of skyglow by snow, particularly in combination with clouds. Snow, however, has a very high albedo and can become important when the direct upward emission is reduced when using shielded luminaires. In this work, first results of skyglow amplification by fresh snow and clouds measured with all-sky photometry in a suburban area are presented. Amplification factors for the zenith luminance of 188 for snow and clouds in combination and 33 for snow alone were found at this site. The maximum zenith luminance of nearly 250 mcd/m² measured with snow and clouds is a factor of 1000 higher than the commonly used clear sky reference of 0.25 mcd/m². Compared with our darkest zenith luminance of 0.07 mcd/m² measured for overcast conditions in a very remote area, this leads to an overall amplification factor of ca. 3500. Horizontal illuminance measurements show values of up to 0.79 lx, exceeding maximum possible full-moon illuminance levels by more than a factor of two. Additional measurements near the Arctic Circle for clear and overcast conditions are presented and strategies for further studies are discussed. We propose the term “snowglow” to describe the amplification of skyglow by snow with and without clouds. Full article

Since the introduction of electric lighting over a century ago, and particularly in the decades following the Second World War, indications of artificial light on the nighttime Earth as seen from Earth orbit have increased at a rate exceeding that of world population growth during the same period. Modification of the natural photic environment at night is a clear and imminent consequence of the proliferation of anthropogenic light at night into outdoor spaces, and with this unprecedented change comes a host of known and suspected ecological consequences. In the past two decades, the conservation community has gradually come to view light pollution as a threat requiring the development of best management practices. Establishing those practices demands a means of quantifying the problem, identifying polluting sources, and monitoring the evolution of their impacts through time. The proliferation of solid-state lighting and the changes to source spectral power distribution it has brought relative to legacy lighting technologies add the complication of color to the overall situation. In this paper, I describe the challenge of quantifying light pollution threats to ecologically-sensitive sites in the context of efforts to conserve natural nighttime darkness, assess the current state of the art in detection and imaging technology as applied to this realm, review some recent innovations, and consider future prospects for imaging approaches to provide substantial support for darkness conservation initiatives around the world. Full article

The rapid growth in electric light usage across the globe has led to increasing presence of artificial light in natural and semi-natural ecosystems at night. This occurs both due to direct illumination and skyglow - scattered light in the atmosphere. There is increasing concern about the effects of artificial light on biological processes, biodiversity and the functioning of ecosystems. We combine intercalibrated Defense Meteorological Satellite Program’s Operational Linescan System (DMSP/OLS) images of stable night-time lights for the period 1992 to 2012 with a remotely sensed landcover product (GLC2000) to assess recent changes in exposure to artificial light at night in 43 global ecosystem types. We find that Mediterranean-climate ecosystems have experienced the greatest increases in exposure, followed by temperate ecosystems. Boreal, Arctic and montane systems experienced the lowest increases. In tropical and subtropical regions, the greatest increases are in mangroves and subtropical needleleaf and mixed forests, and in arid regions increases are mainly in forest and agricultural areas. The global ecosystems experiencing the greatest increase in exposure to artificial light are already localized and fragmented, and often of particular conservation importance due to high levels of diversity, endemism and rarity. Night time remote sensing can play a key role in identifying the extent to which natural ecosystems are exposed to light pollution. Full article

The stability of radiance measurements taken by the Sky Quality Meter (SQM)was tested under rapidly changing temperature conditions during exposure to a stable lightfield in the laboratory. The reported radiance was found to be negatively correlated withtemperature, but remained within 7% of the initial reported radiance over a temperaturerange of -15 °C to 35 °C, and during temperature changes of -33 °C/h and +70 °C/h.This is smaller than the manufacturer’s quoted unit-to-unit systematic uncertainty of 10%,indicating that the temperature compensation of the SQM is adequate under expected outdoor operating conditions. Full article