The persistent increase of artificial light emissions is causing a progressive brightening of the night sky in most regions of the world. This process is a threat for the long-term sustainability of the scientific and educational activity of ground-based astronomical observatories operating in the optical range. Huge investments in building, scientific and technical workforce, equipment and maintenance can be at risk if the increasing light pollution levels hinder the capability of carrying out the top-level scientific observations for which these key scientific infrastructures were built. Light pollution has other negative consequences, as e.g. biodiversity endangering and the loss of the starry sky for recreational, touristic and preservation of cultural heritage. The traditional light pollution mitigation approach is based on imposing conditions on the photometry of individual sources, but the aggregated effects of all sources in the territory surrounding the observatories are seldom addressed in the regulations. We propose that this approach shall be complemented with a top-down, ambient artificial skyglow immission limits strategy, whereby clear limits are established to the admissible deterioration of the night sky above the observatories. We describe the general form of the indicators that can be employed to this end, and develop linear models relating their values to the artificial emissions across the territory. This approach can be easily applied to other protection needs, like e.g. to protect nocturnal ecosystems, and it is expected to be useful for making informed decisions on public lighting, in the context of wider spatial planning projects.

人造光排放的持续增加正在导致世界上大多数地区的夜空逐渐变亮。这个过程对在光学范围内运行的地面天文台的科学和教育活动的长期可持续性构成威胁。如果不断增加的光污染水平阻碍了进行构建这些关键科学基础设施的顶级科学观测的能力，则对建筑，科学技术人员，设备和维护的巨大投资可能会面临风险。光污染还具有其他负面影响，例如危害生物多样性和娱乐，旅游和保护文化遗产的繁星点点的天空。传统的减轻光污染的方法是基于对单个光源的光度法施加条件，但是法规很少涉及到天文台周围区域中所有光源的总效应。我们建议，此方法应辅以自上而下的周围环境人工天辉排放限值策略，从而为观测台上方夜空的可允许恶化设定明确的限值。我们描述了可用于此目的的指标的一般形式，并开发了线性模型，将其值与整个地区的人为排放相关。这种方法可以轻松地应用于其他保护需求，例如保护夜间生态系统，并且有望在做出有关公共照明的明智决定时有用，