Dark Sky Ireland Research and Publications

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.

Public lighting accounts for €56 million in public expenditure annually and is a major item in council budgets. A large proportion of the 480,000 units in the lighting stock are in need of replacement with more efficient luminaires in order to meet energy and carbon reduction targets. The following document is predicated on the assumption that LED lighting will be increasingly used for public lighting and aims to mitigate the negative effects within the constraints of the drive for energy efficiency and lower carbon production. It is important to point out, however, that in line with the recommendations of bodies such as the Institution of Lighting Professionals the greatest savings will be made by dimming lights or removing unnecessary lighting. This document outlines aspects of public lighting in relation to the installation of LED lighting and the desirability to reduce both light levels and the blue spectral component. LED technology is known to have positive outcomes in terms of economic and environmental aspects (including carbon dioxide reduction) and the replacement of older lanterns with modern full cut-off designs which reduce or eliminate light emission above or near the horizontal provide further gains. We suggest that besides the introduction of this technology and also “trimming and dimming” of lighting levels, the colour of the spectrum produced by LED installations and its relationship to the behaviour of human vision at low light levels should be considered when specifying and installing exterior lighting. Consideration of lighting colour and its impact can lead to a reduction in the level of lighting, its impact on the environment, and also potentially reduce human health effects such as sleep disruption. As we have closely followed UK practice in the past, we reference some recent developments, including reduced light levels as specified in BS5489 and also the forthcoming introduction of warmer colour LED lighting in residential areas. A large-scale statistical study of the effect of new lighting practices in England and Wales has detected no change in overall crime or traffic collisions due to restricted light levels and the introduction of white light. We recommend that luminaires with a correlated colour temperature (CCT) of 4000K operate at reduced lumen levels to take account of the increased blue light sensitivity of the human visual response. Such a reduction will lead to further energy savings as well as improved outcome environmentally. In keeping with developing UK practise we suggest that, as a general rule, LED luminaires with warmer colours (i.e., CCT values at or below 3000K) be specified for future installations. Finally, we recommend that pilot lighting schemes be tested in situ to verify the overall lighting design before rolling out more generally. 

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.

Light pollution; ecological effects; protected habitats and species; spatial analysis; Ireland.

The increasing trend of artificial light in the night sky is of global concern. The ecological impacts of light pollution in Ireland has not yet been established. Previous studies have been carried out in rural Ireland in County Mayo, however studies have not been carried out in urban Ireland. Increases in artificial light in the night sky can have both ecological and human impacts. Artificial light levels can alter a number of behaviours in humans, flora and fauna. Disruptions can occur to the circadian rhythm, migration patterns, orientation ability and predator-prey relationships of species. Light level trends in Ireland were determined through the use of satellite imagery of the night sky provided by the Defence Meteorological Satellite Program’s Operational Linescan System (DMSP/OLS). Imagery for the year 1992 which was the first year of the programme was compared to 2013 imagery showing the most recent night sky satellite imagery. A significant increase in light levels was recorded across Ireland over the two decades. Further analysis of the phases of the “Celtic Tiger” (2001-pre “Celtic Tiger”, 2007-“Celtic Tiger”and 2013-post “Celtic Tiger”) showed a great increase in light levels leading up to the year 2007 when construction in Ireland was carried out intensively. Examination of the light levels in Ireland was carried out with the use of Sky Quality Meters (SQM) at three locations to determine the levels of light in the night sky of Dublin. A number of selected species were chosen for this study to identify any possible ecological impact to these species as a results of artificial light pollution. High levels of light in the night sky was recorded at all three light meter locations. The levels of light recorded were well out of the range provided by the International Dark-Sky Association (IDA) for the designation of these areas as dark sky reserves/parks. These high levels are a risk to all the protected species selected in this study. These risks include disruption to migration patterns, reproduction alterations and some species listed may be impacted indirectly. To further develop knowledge of the ecological impacts of light further studies like this are required in Ireland to develop a national light pollution database that will assist in tackling both the increasing level and concerns regarding light pollution. Without establishing a knowledge of the ecological impacts of light pollution appropriate conservation measures cannot be put in place.

Light Pollution; Light sensitivity; Behavioural changes; Ecological impacts; Spatial analysis; Ireland.

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.

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.

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.