Using all-sky differential photometry to investigate how nocturnal clouds darken the night sky in rural areas

Abstract

Artificial light at night has affected most of the natural nocturnal landscapes worldwide and the subsequent light pollution has diverse effects on flora, fauna and human well-being. To evaluate the environmental impacts of light pollution, it is crucial to understand both the natural and artificial components of light at night under all weather conditions. The night sky brightness for clear skies is relatively well understood and a reference point for a lower limit is defined. However, no such reference point exists for cloudy skies. While some studies have examined the brightening of the night sky by clouds in urban areas, the published data on the (natural) darkening by clouds is very sparse. Knowledge of reference points for the illumination of natural nocturnal environments however, is essential for experimental design and ecological modeling to assess the impacts of light pollution. Here we use differential all-sky photometry with a commercial digital camera to investigate how clouds darken sky brightness at two rural sites. The spatially resolved data enables us to identify and study the nearly unpolluted parts of the sky and to set an upper limit on ground illumination for overcast nights at sites without light pollution.

Artificial Light at Night Influences Clock-Gene Expression, Activity, and Fecundity in the Mosquito Culex pipiens f. molestus

“…The mosquitos in the control experienced 0.0 lx. Typical brightness values during the night range from a maximum illuminance of 0.3 lx at a full-moon night [53], which decreases to about 0.001 lx at a moonless clear night [52] and even further for cloudy conditions [54]. This 3.5 h period began when light had decreased to 1% of the mid-day level, at which point light returned to 300 lux (Figure 2A) or 100 lux (activity experiment, Figure 2B) (transition time 10 s) and remained constant for 3.5 h in the "extra light" treatment.…”

How dark is a river? Artificial light at night in aquatic systems and the need for comprehensive night‐time light measurements

“…A general problem of optical remote sensing is cloud cover that prevents detection of light emitted from the Earth surface both night and day. However, clouds can dramatically amplify the effects of skyglow increasing the downwelling part of ALAN (Jechow & Hölker, ; Jechow, Hölker, & Kyba, ; Jechow, Kolláth, Ribas, et al, ; Secondi et al, ). The extent of this effect can only be detected by ground‐based light measurements.…”

“…During the day it ranges from a maximum of about 100,000 lx to about 800 lx at sunset. At night it reaches a maximum of about 0.3 lx at a full‐moon night, decreases to about 0.001 lx at a moonless clear night (Hänel et al, ) and even further for cloudy conditions (Jechow & Hölker, ; Jechow, Hölker, & Kyba, ). The light cycle between night and day, the lunar cycle, weather or seasons serve as external cues (zeitgeber) for cyclic biological processes such as reproduction and foraging (Kronfeld‐Schor & Dayan, ; Robert, Lesku, Partecke, & Chambers, ).…”

Beyond All-Sky: Assessing Ecological Light Pollution Using Multi-Spectral Full-Sphere Fisheye Lens Imaging

“…The measurement position was 53 • 08 34.9" N 13 • 01 41.1" E and images were obtained on 16.08.2016 between 01:22 and 01:26 local time (GMT +2). A more detailed description of the site and surroundings can be found in previous publications [27,39]. (Figure 7e).…”