Parts of Geneva in Switzerland will go darker than normal tonight to bring awareness to the effects of light pollution on cities.
The idea is to turn off lights to let locals stargaze and learn more about conserving energy.
City authorities, Geneva's natural history museum and a local astronomical society are behind the initiative.
It will see more than 150 districts of the Greater Geneva area — which straddles the French-Swiss border — take part.
The big turn off will not see the city go completely dark, however. Only lights not essential to traffic or public safety will be cut.
The districts in France will cut lights over the whole night, while those in Geneva will turn them back on at midnight.
Extra police will be on duty during the night, and the lights will be turned back on if there is a "major incident".
Residential lights will also not be affected.
“After the pollution of the water in the last 60 years and of the air in the last century, the time has come to acknowledge the effect of light pollution,” said Pascal Moeschler, a conservationist at Geneva's natural history museum.
Moeschler and Eric Achkar, president of Geneva’s Astronomical Society (SAG), came up with “La nuit est belle” ("The night is beautiful") to draw attention to the effects of light pollution on the environment, the public’s health and energy consumption.
The event's organisers claim that the region will save a combined 70,000 kWh of energy by turning off their public lights, 20,000 kWh in Geneva, 40,000 kWh in France and 10,000 kWh in Vaud.
There will be several educational events held throughout the night, including stargazing, as both Saturn and Jupiter could be visible.