The world is losing its night sky. A new study published in Science calculated that between 2011 and 2022, global sky brightness increased by about 9.6% per year. Researchers leveraged the community science project Globe at Night and collected data from more than 50,000 people from around the world who recorded the number of stars they saw on clear, dark nights. The study revealed a certain place-to-place variability: Europe saw a 6.5% increase in light pollution per year, while North America faced a 10,4% increase. The global average of 9.6% means sky brightness is doubling about every seven years, and this is not good news. “Increasing sky brightness is a sign we are doing lighting wrong. It’s a sign we are using energy inefficiently, wasting money, exacerbating climate change, and increasing environmental impacts,” states the International Dark Sky Association (IDA). Over lighted districts and streets affect human health by possibly triggering insomnia and other diseases, but it also has negative impacts on animals and plants, disrupting wildlife, the migrations of birds, the blossoming of flowers, and more. We may object that increased light at night improves safety and discourages crime – but having bright, empty parking lots may serve little purpose. The true question is not about more lighting in our cities, but about more intelligent lighting. As streetlights are deemed useful and necessary, IDA advises cities for responsible outdoor lighting following a simple principle: light where and when you need it, in the necessary amount, and no more. “With dimmers, movement sensors and more, the tools exist to light our nights differently,” writes professor Paul Bogard on the Washington Post. Indeed, smart technologies can help a lot. By connecting lamps and controlling them from remote, cities can define customized lighting patterns for single districts and areas. Streetlights can be turned on/off and dimmed according to programmed schedules (ie. setting a default combination for working and festive days, for residential and industrial areas, etc.), changing them whenever necessary to mirror specific local circumstances or events. Specific sensors allow brightness to be adjusted upon ambient light levels. Lamps may also be integrated with motion sensors, vehicle counters, tilt sensors, and other devices, triggering condition-based dynamic lighting. This is particularly useful in low-traffic areas, where lights may be further dimmed only when no vehicle or pedestrian is passing by.