Artificial light at night can be harmful to the environment, and interferes with fauna and flora, star visibility, and human health. To estimate the relative impact of a lighting device, its radiant power, angular photometry and detailed spectral power distribution have to be considered. In this paper we focus on the spectral power distribution. While specific spectral characteristics can be considered harmful during the night, they can be considered advantageous during the day. As an example, while blue-rich Metal Halide lamps can be problematic for human health, star visibility and vegetation photosynthesis during the night, they can be highly appropriate during the day for plant growth and light therapy. In this paper we propose three new indices to characterize lamp spectra. These indices have been designed to allow a quick estimation of the potential impact of a lamp spectrum on melatonin suppression, photosynthesis, and star visibility. We used these new indices to compare various lighting technologies objectively. We also considered the transformation of such indices according to the propagation of light into the atmosphere as a function of distance to the observer. Among other results, we found that low pressure sodium, phosphor-converted amber light emitting diodes (LED) and LED 2700 K lamps filtered with the new Ledtech’s Equilib filter showed a lower or equivalent potential impact on melatonin suppression and star visibility in comparison to high pressure sodium lamps. Low pressure sodium, LED 5000 K-filtered and LED 2700 K-filtered lamps had a lower impact on photosynthesis than did high pressure sodium lamps. Finally, we propose these indices as new standards for the lighting industry to be used in characterizing their lighting technologies. We hope that their use will favor the design of new environmentally and health-friendly lighting technologies.

Propagation of artificial light at night (ALAN) in the environment is now known to have non negligible consequences on fauna, flora and human health. These consequences depend on light levels and their spectral power distributions, which in turn rely on the efficiency of various physical processes involved in the radiative transfer of this light into the atmosphere and its interactions with the built and natural environment. ALAN can affect the living organisms by direct lighting and indirect lighting (scattered by the sky and clouds and/or reflected by local surfaces). This paper mainly focuses on the behaviour of the indirect light scattered under clear sky conditions. Various interaction processes between anthropogenic light sources and the natural environment are discussed. This work mostly relies on a sensitivity analysis conducted with the light pollution radiative transfer model, Illumina (Aubé et al . 2005 Light pollution modelling and detection in a heterogeneous environment: toward a night-time aerosol optical depth retrieval method. In Proc. SPIE 2005, vol. 5890, San Diego, California, USA). More specifically, the impact of (i) the molecular and aerosol scattering and absorption, (ii) the second order of scattering, (iii) the topography and obstacle blocking, (iv) the ground reflectance and (v) the spectrum of light devices and their angular emission functions are examined. This analysis considers different behaviour as a function of the distance from the city centre, along with different zenith viewing angles in the principal plane.

The propagation of artificial light into real environments is complex. To perform its numerical modelling with accuracy, one must consider hyperspectral properties of the lighting devices and their geographic positions, the hyperspectral properties of the ground reflectance, the size and distribution of small-scale obstacles, the blocking effect of topography, the lamps angular photometry and the atmospheric transfer function (aerosols and molecules). A detailed radiative transfer model can be used to evaluate how a particular change in the lighting infrastructure may affect the sky radiance. In this paper, we use the new version (v2) of the Illumina model to evaluate a night sky restoration plan for the Teide Observatory located on the island of Tenerife, Spain. In the past decades, the sky darkness was severely degraded by growing light pollution on the Tenerife Island. In this work, we use the contribution maps giving the effect of each pixel of the territory to the artificial sky radiance. We exploit the hyperspectral capabilities of Illumina v2 and show how the contribution maps can be integrated over regions or municipalities according to the Johnson–Cousins photometric bands spectral sensitivities. The sky brightness reductions per municipality after a complete shutdown and a conversion to light-emitting diodes are calculated in the Johnson–Cousins B, V, R bands. We found that the conversion of the lighting infrastructure of Tenerife with LED (1800 and 2700 K), according to the conversion strategy in force, would result in a zenith V-band sky brightness reduction of ≈0.3 mag arcsec⁻².

Increased exposure to artificial light at night can affect human health including disruption of melatonin production and circadian rhythms which can extend to increased risks of hormonal cancers and other serious diseases. In addition, multiple negative impacts on fauna and flora are well documented, and it is a matter of fact that artificial light at night is a nuisance for ground-based astronomy. These impacts are frequently linked to the colour of the light or more specifically to its spectral content. Artificial light at night is often mapped by using spaceborne sensors, but most of them are panchromatic and thus insensitive to the colour. In this paper, we suggest a method that allows high-resolution mapping of the artificial light at night by using ground-based measurements with the LANcube system. The newly developed device separates the light detected in four bands (Red, Green, Blue and Clear) and provides this information for six faces of a cube. We found relationships between the LANcube’s colour ratios and (1) the Melatonin Suppression Index, (2) the StarLight Index and (3) the Induced Photosynthesis Index. We show how such relationships combined with data acquisition from a LANcube positioned on the top of a car can be used to produce spectral indices maps of a whole city in a few hours.

Knowledge of the night sky radiance over a large region may be valuable information for identifying sites suitable for astronomical observations or for assessing the impact of artificial light at night on ecosystems. Measuring the sky radiance can be a complex endeavour, depending on the desired temporal and spatial resolution. Likewise, the modelling of artificial night sky radiance for multiple points of a region can represent a significant amount of computing time depending on the complexity of the model used. The use of the convolution of a point spread function with the geographical distribution of light sources has been suggested in order to model the sky radiance over large territories of hundreds of kilometres in size. We determined how the point spread function is sensitive to the main driving parameters of the artificial night sky radiance, such as the wavelength, the ground reflectance, the obstacle properties, the upward light output ratio, and the aerosol optical depth using the Illumina v2 model. The obtained functions were then used to model the artificial night sky brightness of the Mont-Mégantic International Dark Sky Reserve for winter and summer conditions. The results were compared with the New World Atlas of artificial night sky brightness, the Illumina v2 model, and in situ Sky Quality Camera measurements. We found that the New World Atlas overestimates the artificial sky brightness by 55 per cent, whereas the Illumina model underestimates it by 48 per cent. This may be due to varying atmospheric conditions and the fact that the model accounts only for public light sources.

The goal of this study is to evaluate the current level of light pollution in the night sky at the Haleakala Observatory on the island of Maui in Hawaii. This is accomplished with a numerical model that was tested in the first International Dark Sky Reserve located in Mont-Mégantic National Park in Canada. The model uses ground data on the artificial light sources present in the region of study, geographical data, and remotely sensed data for (1) The nightly upward radiance, (2) The terrain elevation, and 3) The ground spectral reflectance of the region. The results of the model give a measure of the current state of the sky spectral radiance at the Haleakala Observatory. Then, using the current state as a reference point, multiple light conversion plans are elaborated and evaluated using the model. We can thus estimate the expected impact of each conversion plan on the night sky radiance spectrum. A complete conversion to white light emitting diodes (LEDs) with correlated colour temperature of 4000 and 3000 K are contrasted with a conversion using phosphore-convertred amber LEDs. We include recommendations concerning the street lamps to be used in sensitive areas like the cities of Kahului and Kihei, and suggest best lighting practices related to the colour of lamps used at night.