Darkness card, sky brightness with greenhouse lighting off

The map concerns the sky brightness in North Holland in 2011-2012 with greenhouse lighting off. If there is no direct enlightenment nearby, the night sky determines the degree of darkness. The sky is lit up by shining light from a city or greenhouse from an area with a radius of about 30 kilometers. In 2011 and 2012, 225 locations in the province of North Holland measured the brightness of the sky in the point straight up (zenit), as a measure of the ‘darkness’. Previously carried out measurements in Amsterdam and on the island of Texel have also been incorporated into this darkness map.本数据集对应的可视化地图展示了2011至2012年荷兰北荷兰省（North Holland）在温室照明关停状态下的天空亮度分布。若无邻近区域的直接人工光照，夜空亮度可作为衡量暗夜程度的核心指标。方圆约30公里范围内的城市或温室所辐射的光线，将对该区域天空亮度产生照明影响。2011至2012年间，研究人员在北荷兰省的225个测点对天顶（zenit）方向的天空亮度进行了测量，以此作为“暗夜程度”的量化依据。此前在阿姆斯特丹（Amsterdam）及特塞尔岛（Texel）完成的观测数据，也已被纳入该暗夜亮度地图数据集。