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Bará, S. (2014). Naked-eye astronomy: optics of the starry night skies. Proc. SPIE 9289, 9289.
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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Bará, S. (2014). Light pollution and solid-state lighting: reducing the carbon dioxide footprint is not enough. Proc. SPIE 8785, 8785.
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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Lyytimäki, J. (2015). Avoiding overly bright future: The systems intelligence perspective on the management of light pollution. Environmental Development, 16, 4–14.
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Bará, S., Ribas, S., & Kocifaj, M. (2015). Modal evaluation of the anthropogenic night sky brightness at arbitrary distances from a light source. J. of Optics, 17, 105607.
Abstract: The artificial emissions of light contribute to a high extent to the observed brightness of the night sky in many places of the world. Determining the all-sky radiance of anthropogenic origin requires solving the radiative transfer equation for ground-level light sources, generally resorting to a double-scattering approximation in order to account for the observed radiance patterns with a reasonable degree of accuracy. Since the all-sky radiance distribution produced by an elementary light source depends on the distance to the observer in a way that is not immediately obvious, the contributions of sources located at different distances have to be computed on an individual basis, solving for each one the corresponding scattering integrals. In this paper we show that these calculations may be significantly alleviated by using a modal approach, whereby the hemispheric night-sky radiance is expanded in terms of a convenient basis of two-dimensional (2D) orthogonal functions. Since the modal coefficients of this expansion do vary smoothly with the distance to the observer, the all-sky brightness distributions produced by light sources located at arbitrary intermediate distances can be efficiently estimated by interpolation, provided that the coefficients at a discrete set of distances are accurately determined beforehand.
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Ouyang, J. Q., Maaike de Jong, M. H., Visser, M. E., van Grunsven, R. H. A., & Ouyang, J. Q. (2015). Stressful colours: corticosterone concentrations in a free-living songbird vary with the spectral composition of experimental illumination. Biol. Lett., 11, 20150517.
Abstract: Organisms have evolved under natural daily light/dark cycles for millions of years. These cycles have been disturbed as night-time darkness is increasingly replaced by artificial illumination. Investigating the physiological consequences of free-living organisms in artificially lit environments is crucial to determine whether nocturnal lighting disrupts circadian rhythms, changes behaviour, reduces fitness and ultimately affects population numbers. We make use of a unique, large-scale network of replicated field sites which were experimentally illuminated at night using lampposts emanating either red, green, white or no light to test effect on stress hormone concentrations (corticosterone) in a songbird, the great tit (Parus major). Adults nesting in white-light transects had higher corticosterone concentrations than in the other treatments. We also found a significant interaction between distance to the closest lamppost and treatment type: individuals in red light had higher corticosterone levels when they nested closer to the lamppost than individuals nesting farther away, a decline not observed in the green or dark treatment. Individuals with high corticosterone levels had fewer fledglings, irrespective of treatment. These results show that artificial light can induce changes in individual hormonal phenotype. As these effects vary considerably with light spectrum, it opens the possibility to mitigate these effects by selecting street lighting of specific spectra.
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