| Records |
Author  |
Bará, S.; Aubé, M.; Barentine, J.; Zamorano, J. |
| Title |
Magnitude to luminance conversions and visual brightness of the night sky |
Type |
Journal Article |
| Year |
2020 |
Publication |
Monthly Notices of the Royal Astronomical Society |
Abbreviated Journal |
MNRAS |
| Volume |
493 |
Issue |
2 |
Pages |
2429–2437 |
| Keywords |
Skyglow; light pollution; atmospheric effects; techniques: photometric; methods: numerical; luminance |
| Abstract |
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 × 105 cd m−2 if mV is reported in the absolute (AB) magnitude scale, and between 1.18–1.43 × 105 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 μcd m−2 (AB), or 187 and 227 μcd 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. |
| Address |
Departamento de Física Aplicada, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Galicia; salva.bara(at)usc.gal |
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| Publisher |
Oxford Academic |
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| Language |
English |
Summary Language |
English |
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| Call Number |
IDA @ john @ |
Serial |
2825 |
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| Author |
Bará, S.; Escofet, J. |
| Title |
On lamps, walls, and eyes: The spectral radiance field and the evaluation of light pollution indoors |
Type |
Journal Article |
| Year |
2018 |
Publication |
Journal of Quantitative Spectroscopy and Radiative Transfer |
Abbreviated Journal |
J of Quant Spect and Rad Trans |
| Volume |
205 |
Issue |
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Pages |
267-277 |
| Keywords |
Instrumentation; Light pollution; Artificial light at night; Light field; Radiance field; Radiometry; Photometry |
| Abstract |
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. |
| Address |
Área de Óptica, Departamento de Física Aplicada, Universidade de Santiago de Compostela, Santiago de Compostela, Galicia, Spain; salva.bara(at)usc.es |
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Elsevier |
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| Language |
English |
Summary Language |
English |
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0022-4073 |
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no |
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IDA @ john @ |
Serial |
2163 |
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| Author |
Bará, S.; Falchi, F.; Furgoni, R.; Lima, R.C. |
| Title |
Fast Fourier-transform calculation of artificial night sky brightness maps |
Type |
Journal Article |
| Year |
2020 |
Publication |
Journal of Quantitative Spectroscopy and Radiative Transfer |
Abbreviated Journal |
Journal of Quantitative Spectroscopy and Radiative Transfer |
| Volume |
240 |
Issue |
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Pages |
106658 |
| Keywords |
Skyglow; Light pollution; Atmospheric optics; Photometry; Radiometry; Fourier transforms |
| Abstract |
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. |
| Address |
Departamento de Física Aplicada, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Galicia, Spain; salva.bara(at)usc.es |
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Elsevier |
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English |
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English |
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0022-4073 |
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Approved |
no |
| Call Number |
IDA @ john @ |
Serial |
2782 |
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| Author |
Bará, S.; Lima, R.C. |
| Title |
Photons without borders: quantifying light pollution transfer between territories |
Type |
Journal Article |
| Year |
2018 |
Publication |
International Journal of Sustainable Lighting |
Abbreviated Journal |
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| Volume |
20 |
Issue |
2 |
Pages |
51-61 |
| Keywords |
Skyglow |
| Abstract |
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. |
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NC @ ehyde3 @ |
Serial |
2066 |
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| Author |
Bará, S.; Lima, R.C.; Zamorano, J. |
| Title |
Monitoring Long-Term Trends in the Anthropogenic Night Sky Brightness |
Type |
Journal Article |
| Year |
2019 |
Publication |
Sustainability |
Abbreviated Journal |
Sustainability |
| Volume |
11 |
Issue |
11 |
Pages |
3070 |
| Keywords |
Skyglow |
| Abstract |
Monitoring long-term trends in the evolution of the anthropogenic night sky brightness is a demanding task due to the high dynamic range of the artificial and natural light emissions and the high variability of the atmospheric conditions that determine the amount of light scattered in the direction of the observer. In this paper, we analyze the use of a statistical indicator, the mFWHM, to assess the night sky brightness changes over periods of time larger than one year. The mFWHM is formally defined as the average value of the recorded magnitudes contained within the full width at half-maximum region of the histogram peak corresponding to the scattering of artificial light under clear skies in the conditions of a moonless astronomical night (sun below −18°, and moon below −5°). We apply this indicator to the measurements acquired by the 14 SQM detectors of the Galician Night Sky Brightness Monitoring Network during the period 2015–2018. Overall, the available data suggest that the zenithal readings in the Sky Quality Meter (SQM) device-specific photometric band tended to increase during this period of time at an average rate of +0.09 magSQM/arcsec2 per year. |
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2071-1050 |
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GFZ @ kyba @ |
Serial |
2552 |
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