Anthropogenic skyglow dominates views of the natural night sky in most urban settings, and the associated emission of artificial light at night (ALAN) into the environment of cities involves a number of known and suspected negative externalities. One approach to lowering consumption of ALAN in cities is dimming or extinguishing publicly owned outdoor lighting during overnight hours; however, there are few reports in the literature about the efficacy of these programs. Here we report the results of one of the largest municipal lighting dimming experiments to date, involving ~ 20,000 roadway luminaires owned and operated by the City of Tucson, Arizona, U.S. We analyzed both single-channel and spatially resolved ground-based measurements of broadband night sky radiance obtained during the tests, determining that the zenith sky brightness during the tests decreased by ($-5.4\pm 0.9$)% near the city center and ($-3.6\pm 0.9$)% at an adjacent suburban location on nights when the output of the street lighting system was dimmed from 90% of its full power draw to 30% after local midnight. Modeling these changes with a radiative transfer code yields results suggesting that street lights account for about (14 ± 1)% of light emissions resulting in skyglow seen over the city. A separate derivation from first principles implies that street lighting contributes only $2-3$% of light seen at the zenith over Tucson. We discuss this inconsistency and suggest routes for future work.

在大多数城市环境中，人为的天辉在自然夜空的视野中占主导地位，而夜间向城市环境中发射的人造光（ALAN）的相关辐射涉及许多已知和怀疑的负面外部性。降低城市ALAN消耗的一种方法是在通宵的夜晚调暗或熄灭公共拥有的户外照明设备。但是，关于这些程序的功效的文献报道很少。在这里，我们报告了迄今为止最大的市政照明调光实验之一的结果，涉及美国亚利桑那州图森市拥有和运营的约20,000个道路照明设备。我们分析了宽带夜间单通道和空间分辨的地面测量测试期间获得的天空辐射$-5.4\pm 0.9$）％靠近市中心和（$-3.6\pm 0.9$晚上，在邻近郊区的街道上，当街道照明系统的输出从其全功率消耗的90％减至当地午夜后的30％时，该百分比为30％。用辐射传输代码对这些变化进行建模可得出结果，表明路灯约占光排放量的（14±1）％，导致整个城市都出现了天窗。与第一原理不同的推论意味着，街道照明仅有助于$2-3$图森上空的天顶上看到的光的百分比。我们讨论了这种不一致之处，并为以后的工作提出了建议。