Time Out says
This WWF initiative invites people to turn off their lights between 8.30pm and 9.30pm GMT for Earth Hour 2019 and raise awareness of climate change and the natural world.
Last year, millions of people across 178 countries took part to show their support for the planet with a global 'lights out'. And expect plenty of London landmarks and institutions to get in on the act this year. Find out more on the WWF website.