Light pollution has increased globally, with 80% of the total population now living under light-polluted skies. In this Review, we elucidate the scope and importance of light pollution and discuss techniques to monitor it. In urban areas, light emissions from sources such as street lights lead to a zenith radiance 40 times larger than that of an unpolluted night sky. Non-urban areas account for over 50% of the total night-time light observed by satellites, with contributions from sources such as transportation networks and resource extraction. Artificial light can disturb the migratory and reproductive behaviours of animals even at the low illuminances from diffuse skyglow. Additionally, lighting (indoor and outdoor) accounts for 20% of global electricity consumption and 6% of CO2 emissions, leading to indirect environmental impacts and a financial cost. However, existing monitoring techniques can only perform a limited number of measurements throughout the night and lack spectral and spatial resolution. Therefore, satellites with improved spectral and spatial resolution are needed to enable time series analysis of light pollution trends throughout the night. Increasing light emissions threaten human and ecological health. This Review outlines existing measurements and projections of light pollution trends and impacts, as well as developments in ground-based and remote sensing techniques that are needed to improve them.

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.

Exposure to artificial light-at-night (ALAN) is increasing globally, and there are concerns around how ALAN may impact sleep, psychological and physical health. However, there is a lack of evidence in the literature on how individuals perceive ALAN relative to their sleeping environment and habits, and how such perceptions correspond to objectively assessed night-time illuminance at the level of the residence. This cross-sectional study examined how such perceptions associate with sleep quality, sleep timing, psychological distress and cognitive failures. Further we examined the association between illuminance levels calculated as the biologically-relevant melatonin-suppression index (MSI) and the self-report of perception of ALAN. Five hundred and fifty two adult participants completed a survey addressing perception of ALAN in sleep environment along with the Pittsburgh Sleep Quality Index, Munich Chronotype Questionnaire, Cognitive Failure Questionnaire and the General Health Questionnaire. We report that perception of external ALAN in the sleeping environment was associated with poorer sleep quality, more cognitive failures and greater psychological distress, when controlling for age, sex, house location and MSI. No associations were found between the perception of external ALAN and MSI scores, and MSI scores were not associated with scores on any of the self-report measures. Internal lighting passing into the sleeping environment was associated with poorer sleep quality but not with psychological wellbeing. Habitual use of light-emitting devices was associated with poorer psychological wellbeing but not with sleep quality and sleep timing. Perception of environmental noise annoyance at night was associated with higher psychological distress and poorer quality sleep, and the perception of noise annoyance was associated with perception of ALAN. These results may suggest heightened attentional bias towards ALAN associated with poor sleep quality and higher levels of psychological distress, and highlight the need for more granular approaches in the study of ALAN and sleep and psychological health in terms of levels individual ALAN exposure, and an interpretation that seeks to integrate biological and psychological perspectives.

The spatial and angular emission patterns of artificial and natural light emitted, scattered, and reflected from the Earth at night are far more complex than those for scattered and reflected solar radiation during daytime. In this commentary, we use examples to show that there is additional information contained in the angular distribution of emitted light. We argue that this information could be used to improve existing remote sensing retrievals based on night lights, and in some cases could make entirely new remote sensing analyses possible. This work will be challenging, so we hope this article will encourage researchers and funding agencies to pursue further study of how multi‐angle views can be analyzed or acquired.

Nighttime light emissions are increasing in most countries worldwide, but which types of lighting are responsible for the increase remains unknown. Also unknown is what fraction of outdoor light emissions and associated energy use are due to public light sources (i.e. streetlights) or various types of private light sources (e.g. advertising). Here we show that it is possible to measure the contribution of street lighting to nighttime satellite imagery using ‘smart city’ lighting infrastructure. The city of Tucson, USA, intentionally altered its streetlight output over 10 days, and we examined the change in emissions observed by satellite. We find that streetlights operated by the city are responsible for only 13% of the total radiance (in the 500–900 nm band) observed from Tucson from space after midnight (95% confidence interval 10–16%). If Tucson did not dim their streetlights after midnight, the contribution would be 18% (95% confidence interval 15–23%). When streetlights operated by other actors are included, the best estimates rise to 16% and 21%, respectively. Existing energy and lighting policy related to the sustainability of outdoor light use has mainly focused on street lighting. These results suggest an urgent need for consideration of other types of light sources in outdoor lighting policy.

Study of light at night has increased in recent decades due to the recognition of its impact on the environment, potential health concerns, as well as both the financial and carbon cost of energy waste. The advent of more extensive and improved ground-based measurements together with quantifiable satellite data has revolutionised the field, and provided data to test improved theoretical models. However, “closing the loop” and finding a detailed connection between these measurements requires knowledge of the “city emission function”, the angular distribution of upwelling radiation with zenith distance. Simplified analytical functions have been superseded by more complex models involving statistical approximation of emission sources and obstructions and inversion techniques now permit the estimation of emission functions from the observed sky brightness measurements. In this paper, we present an efficient GIS-based method to model public lighting using real-world photometric data and high-resolution digital elevation maps of obstructions such as buildings and trees at a 1 m scale. We discuss the results of this work for a sample of Irish towns as well as a city area. We also compare our results to previous emission functions as well as to observed asymmetries in emission detected by satellites such as SUOMI VIIRS.

BACKGROUND:Light pollution is increasingly an area of concern for health and quality of life research. Somewhat surprisingly, there are relatively few descriptions of perceptions of light pollution in the literature. The current study examined such perceptions in a Irish sample.METHODS:A survey was circulated as part of a citizen science initiative of a national newspaper; the survey included questions regarding night sky brightness and the impact of light at night on sleep and animal behaviour. Complete responses from 462 respondents were analysed.RESULTS:Urban location was, as anticipated, associated with reported brighter night skies, and public lighting was reported as the main source of light at night for urban settings, whilst neighbours' domestic lighting was the most commonly reported source for rural settings. Respondents from rural settings were more likely to report that light at night impinged on sleep, whilst city dwellers were more likely to report recent changes in wildlife behaviour.CONCLUSIONS:Citizen science approaches may be useful in gathering data on public perceptions of light pollution and its impacts. In the current study, this perception was strongly influenced by location, highlighting the importance of assessing experiences and attitudes across a number of geographical settings.

Increasing use of artificial light at night has led to many areas across the globe being exposed to light conditions above the natural background level. Research is only now uncovering the impacts of ‘ecological light pollution’ on the environment. Artificial light at night can disrupt circadian rhythms, cause interference with orientation and migration, alter predator/prey interactions and affect other behaviour and physiological features. Intercalibration of Defense Meteorological Satellite Program’s Operational Linescan System images shows that night light emissions in Ireland have increased significantly from 1995 to 2010. In this period, artificial light has spread into previously dark rural areas, including County Mayo where 28% of land surface is designated for habitat and species conservation purposes. To investigate light pollution in rural areas, examination into the conservation area of Owenduff/Nephin Beg Complex was undertaken. Spatial analysis of light measurements taken from Sky Quality Meters surrounding the site were overlaid with species distribution records to determine the proximity of protected species to sources of artificial light at night. Light measurements from the area show pristine night skies according to International Dark Sky Association standards, with one site indicating the presence of localised light pollution. Further work is required to determine if any potential adverse ecological impacts on protected species in the locality are occurring from artificial light at night. The findings of this study provide a foundation for ecological light pollution effects assessment in Ireland. Further work is required to establish the temporal and spatial scales of artificial light in Irish rural areas and determine the specific effects on species present there.

The 2014 LoNNe (Loss of the Night Network) intercomparison campaign is the second of four campaigns planned during EU COST Action ES1204. The goal of these campaigns is to understand systematic uncertainty inherent in observations of skyglow (light pollution). An innovation of this year’s campaign was to take measurements with many of the nstruments at two sites: an urban location and a location far from artificial lights. This report summarizes the eeting, and also provides three recommendations for obtaining and analyzing handheld SQM observations. The UCM group of Astronomical Instrumentation and Extragalactic Astronomy (GUAIX) hosted the meeting at the Physics building of Universidad Complutense de Madrid (UCM). A meeting room at Departamento de Astrofisica y CC. de la Atmosfera and the astronomical observatory (Observatorio UCM) were prepared in advance. In particular, a tailor made station to set the SQM and other photometer devices was installed on the roof of the Physics building. The Laboratorio de Investigacion Cientifica Avanzada (LICA) was used to test and characterize a number of devices and filters.

In the Celtic Tiger years, Ireland underwent an explosive growth in housing and an increase in light pollution, nationally. We outline work undertaken towards the first ever ground-based survey of light pollution in the island of Ireland and illustrate this with some representative data taken between 2009 and the present. The aim of our work is to establish a database to serve as a reference to monitor future changes, to compare with in-orbit measurements, to study the potential impact on the environment and to permit the calculation of the effects of future changes in lighting usage and patterns. We also report the development of a microcontroller-based data-logging instrument based on a Unihedron Sky Quality Meter-LR detector, which can be used by amateurs or can serve as a stand-alone instrument for night-sky brightness surveys.

We present preliminary results from recent HST/STIS observations of the symbiotic binary system EG Andromedae (HD4174) and an isolated spectral standard HD148349 (V2105 Oph). We show the similarities between the red giant primary of the binary system and the spectral standard HD 148349 and demonstrate a technique for obtaining contemporaneous low-resolution optical spectra when making UV observations with STIS. We offer new measurements of the differential extinction and brightness ratio between our two target stars as well as a more precise value of the EG And distance. We investigate chromospheric diagnostic emission lines and show how our study of symbiotic stars can be integral to the understanding of mass-loss from isolated red giants.

For those red giants and supergiants which do not exhibit an optically thick circumstellar dust shell, the observation of massive stellar winds remains an outstanding problem. The wind-driving mechanism, as well as many wind characteristics through the wind-acceleration region, are unknown. We discuss the use of eclipsing binary systems to analyze the important regions at the base of the outflow, with reference to work we have carried out on a small sample of red giants in symbiotic binary systems.

We summarise the CS15 splinter session dealing with the winds and chromospheres of cool giant and supergiant stars. The motivation behind the session was to bring together various researchers in the field with the purpose of forming some important common goals for future work, as well as to hear some of the latest results. We provide an overview of the results that were presented and highlight some of the main outcomes of the discussions.

As a star cools and expands to become a red giant it will become pulsationally unstable. The amplitude tends to increase with decreasing temperature as the star ascends the red giant branch. Below around 4,000K (Spectral Type K5III) microvariability sets in. This may have a strong impact on the pulsation-driven mass loss history. We are studying a sample of symbiotic binaries in order to understand the mechanism of mass loss from the red giant primary. Photometric monitoring indicates small-scale variability of around 20% over a timescale of similar to 30 days. This is likely related to the convective motion on the surface which may be directly or indirectly involved in providing the initial impetus to raise material and initiate the wind. Studying this convective motion and its relationship with the wind will improve our understanding of the wind's origin.

Although much is known about the nature of winds from hot stars and giants and supergiants with spectral types earlier than K, there is still much to be learned regarding the mass-loss process in cool, late-type stars. We will review the current state of research, with particular reference to observations and modelling of mass-loss from giant stars in symbiotic systems.

We present highlights and an overview of 20 FUSE and HST STIS observations of the bright symbiotic binary EG And. The main motivation behind this work is to obtain spatially resolved information on an evolved giant star in order to understand the mass-loss processes at work in these objects. The system consists of a low-luminosity white dwarf and a mass-losing, nondusty M2 giant. The ultraviolet observations follow the white dwarf continuum through periodic gradual occultations by the wind and chromosphere of the giant, providing a unique diagnosis of the circumstellar gas in absorption. Unocculted spectra display high-ionization features, such as the O VI resonance doublet, which is present as a variable (hourly timescales), broad wind profile, which diagnose the hot gas close to the dwarf component. Spectra observed at stages of partial occultation display a host of low-ionization, narrow absorption lines, with transitions observed from lower energy levels up to ~5 eV above ground. This absorption is due to chromospheric/wind material, with most lines due to transitions of Si II, P II, N I, Fe II, and Ni II, as well as heavily damped H I Lyman series features. No molecular features are observed in the wind acceleration region despite the sensitivity of FUSE to H2. From analysis of the ultraviolet data set, as well as optical data, we find that the dwarf radiation does not dominate the wind acceleration region of the giant and that observed thermal and dynamic wind properties are most likely representative of isolated red giants.