Abstract: In 2007, the area around the Mont-Mégantic Observatory (MMO) was officially certified by the International Dark-Sky Association and the Royal Astronomy Association of Canada as the first International Dark Sky Reserve (IDSR). In order to be able to investigate the impact of Artificial Light at Night on night sky brightness before and after the establishment of the IDSR, we used a heterogeneous artificial sky brightness model including an implicit calculation of 2nd order scattering (ILLUMINA) developed by Martin Aubé's group. This model generates three kinds of outputs: the sky radiance at the given site, observing angle and wavelength and the corresponding contribution and sensitivity maps. The maps allow for the identification of the origin of the sky radiance according to each part of the surrounding territory. For summer clear sky conditions, the results show that replacing light fixtures within a 25 km radius around the MMO with cut-off High Pressure Sodium devices and reducing the total installed radiant power to ~40% of its initial level are very efficient ways of reducing artificial sky brightness. The artificial sky brightness reduction at zenith observed after the establishment of the IDSR was ~50% in the 546 nm mercury spectral line, while the reduction obtained in the 569 nm sodium line was ~30%. A large part of that reduction can be associated to the reduction in radiant power. The contribution and sensitivity maps highlight critical zones where any changes in the lighting infrastructure have the most important impact on sky brightness at the MMO. Contribution and sensitivity maps have been used to analyze the detailed origin of sky brightness reduction. The results of this study are intended to support authorities in the management of their lighting infrastructure with the goal of reducing sky brightness. The results have been shared with MMO officials and are being used as a tool to improve sky quality at the observatory.

Abstract: A relevant amount of light pollution studies deal with the unwanted visual effects of artificial light at night, including the anthropogenic luminance of the sky that hinders the observation of the celestial bodies which are a main target of ground-based astrophysical research, and a key asset of the intangible heritage of humankind. Most quantitative measurements and numerical models, however, evaluate the anthropogenic sky radiance in any of the standard Johnson-Cousins UBVRI photometric bands, generally in the V one. Since the Johnson-Cousins V band is not identical with the visual CIE V-lambda used to assess luminance, the conversion between these two photometric systems turns out to be spectrum-dependent. Given its interest for practical applications, in this Letter we provide the framework to perform this conversion and the transformation constants for black-body spectra of different absolute temperatures.

Abstract: We develop a general optical model and describe the absolute radiometric calibration of the readings provided by two widely-used night sky brightness sensors based on irradiance-to-frequency conversion. The calibration involves the precise determination of the overall spectral sensitivity of the devices and also the constant G relating the output frequency of the light-to-frequency converter chip to the actual band-weighted and field-of-view averaged spectral radiance incident on the detector (brightness). From these parameters, we show how to define a rigorous astronomical absolute photometric system in which the sensor measurements can be reported in units of magnitudes per square arcsecond with precise physical meaning.