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Author  |
Bará, S. |
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Title |
Naked-eye astronomy: optics of the starry night skies |
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Journal Article |
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Year |
2014 |
Publication |
Proc. SPIE 9289, 12th Education and Training in Optics and Photonics Conference, 2014 |
Abbreviated Journal |
Proc. SPIE 9289 |
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9289 |
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Keywords |
Society; light pollution |
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Abstract |
The world at night offers a wealth of stimuli and opportunities as a resource for Optics education, at all age levels and from any (formal, non formal or informal) perspective. The starry sky and the urban nightscape provide a unique combination of pointlike sources with extremely different emission spectra and brightness levels on a generally darker, locally homogeneous background. This fact, combined with the particular characteristics of the human visual system under mesopic and scotopic conditions, provides a perfect setting for experiencing first-hand different optical phenomena of increasing levels of complexity: from the eye's point spread function to the luminance contrast threshold for source detection, from basic diffraction patterns to the intricate irradiance fluctuations due to atmospheric turbulence. Looking at the nightscape is also a perfect occasion to raise awareness on the increasing levels of light pollution associated to the misuse of public and private artificial light at night, to promote a sustainable use of lighting, and to take part in worldwide citizen science campaigns. Last but not least, night sky observing activities can be planned and developed following a very flexible schedule, allowing individual students to carry them out from home and sharing the results in the classroom as well as organizing social events and night star parties with the active engagement of families and groups of the local community. This contribution describes these possibilities and introduces some of the free resources available to put them in practice. |
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Univ. de Santiago de Compostela, Spain; salva.bara@usc.es |
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SPIE |
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English |
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English |
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IDA @ john @ |
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1134 |
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Author |
Bará, S. |
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Title |
Light pollution and solid-state lighting: reducing the carbon dioxide footprint is not enough |
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Journal Article |
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Year |
2014 |
Publication |
Proc. SPIE 8785, 8th Iberoamerican Optics Meeting and 11th Latin American Meeting on Optics, Lasers, and Applications, 87852G, 2013 |
Abbreviated Journal |
Proc. SPIE 8785 |
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8785 |
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Keywords |
*Lighting; LED; light emitting diode; outdoor lighting; artificial light at night; lighting policy; solid-state lighting; blue light |
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Abstract |
Public and private lighting account for a relevant share of the overall electric power consumption worldwide. The pressing need of reducing the carbon dioxide emissions as well as of lowering the lumen•hour price tag has fostered the search for alternative lighting technologies to substitute for the incandescent and gas-discharge based lamps. The most successful approach to date, solid-state lighting, is already finding its way into the public lighting market, very often helped by substantial public investments and support. LED-based sources have distinct advantages: under controlled conditions their efficacy equals or surpasses that of conventional solutions, their small source size allows for an efficient collimation of the lightbeam (delivering the photons where they are actually needed and reducing lightspill on the surrounding areas), and they can be switched and/or dimmed on demand at very high rates, thus allowing for a tailored schedule of lighting. However, energy savings and carbon dioxide reduction are not the only crucial issues faced by present day lighting. A growing body of research has shown the significance of the spectral composition of light when it comes to assess the detrimental effects of artificial light-at-night (ALAN). The potential ALAN blueshift associated to the deployment of LED-based lighting systems has raised sensible concerns about its scientific, cultural, ecological and public health consequences, which can be further amplified if an increased light consumption is produced due to the rebound effect. This contribution addresses some of the challenges that these issues pose to the Optics and Photonics community. |
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Univ. de Santiago de Compostela, Spain; salva.bara@usc.es |
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SPIE |
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English |
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English |
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IDA @ john @ |
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1135 |
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Author |
Bará, S. |
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Title |
Anthropogenic disruption of the night sky darkness in urban and rural areas |
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Journal Article |
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Year |
2016 |
Publication |
Royal Society Open Science |
Abbreviated Journal |
R. Soc. open sci. |
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3 |
Issue |
10 |
Pages |
160541 |
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Keywords |
Skyglow |
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Abstract |
The growing emissions of artificial light to the atmosphere are producing, among other effects, a significant increase of the night sky brightness (NSB) above its expected natural values. A permanent sensor network has been deployed in Galicia (northwest of Iberian peninsula) to monitor the anthropogenic disruption of the night sky darkness in a countrywide area. The network is composed of 14 detectors integrated in automated weather stations of MeteoGalicia, the Galician public meteorological agency. Zenithal NSB readings are taken every minute and the results are openly available in real time for researchers, interested stakeholders and the public at large through a dedicated website. The measurements allow one to assess the extent of the loss of the natural night in urban, periurban, transition and dark rural sites, as well as its daily and monthly time courses. Two metrics are introduced here to characterize the disruption of the night darkness across the year: the significant magnitude (m1/3) and the moonlight modulation factor (γ). The significant magnitude shows that in clear and moonless nights the zenithal night sky in the analysed urban settings is typically 14–23 times brighter than expected from a nominal natural dark sky. This factor lies in the range 7–8 in periurban sites, 1.6–2.5 in transition regions and 0.8–1.6 in rural and mountain dark sky places. The presence of clouds in urban areas strongly enhances the amount of scattered light, easily reaching amplification factors in excess of 25, in comparison with the light scattered in the same places under clear sky conditions. The periodic NSB modulation due to the Moon, still clearly visible in transition and rural places, is barely notable at periurban locations and is practically lost at urban sites. |
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2054-5703 |
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Call Number |
LoNNe @ kyba @ |
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1544 |
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Author |
Bará, S. |
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Title |
Variations on a classical theme: On the formal relationship between magnitudes per square arcsecond and luminance |
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Journal Article |
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Year |
2017 |
Publication |
International Journal of Sustainable Lighting |
Abbreviated Journal |
Intl J of Sustainable Lighting |
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Volume |
19 |
Issue |
2 |
Pages |
77 |
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Keywords |
Instrumentation; skyglow; luminance; magnitude; sky brigthness; photometry |
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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(l) 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 last ones be measured precisely in the CIE V(l) band. The luminance value corresponding to mVC=0 (zero-point of the CIE V(l) 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(l) photometric band is 10.96 x 104 cd·m-2. |
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Departamento de Física Aplicada, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Galicia, Spain; salva.bara(at)usc.es |
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English |
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English |
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ISSN |
2586-1247 |
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Call Number |
IDA @ john @ |
Serial |
2162 |
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Author |
Bará, S. |
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Title |
Characterizing the zenithal night sky brightness in large territories: how many samples per square kilometre are needed? |
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Journal Article |
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Year |
2017 |
Publication |
Monthly Notices of the Royal Astronomical Society |
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473 |
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3 |
Pages |
4164-4173 |
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Keywords |
Instrumentation; atmospheric effects; light pollution; numerical methods; photometry |
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Abstract |
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 kilometre 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 analysis of several regions of the world, based on the data from the New world atlas of artificial night sky brightness, suggests that, as a rule of thumb, about one measurement per square kilometre could be sufficient for determining the zenithal night sky brightness of artificial origin at any point in a region to within ±0.1 magV arcsec–2 (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. |
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1Departamento de Física Aplicada, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Galicia, Spain; salva.bara(at)usc.es |
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Oxford Academic |
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English |
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English |
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0035-8711 |
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Call Number |
IDA @ john @ |
Serial |
2164 |
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