Big Ben, the Houses of Parliament, the Gherkin, Piccadilly Circus, Harrods and the Ritz are all expected to take part in the capital's blackout, which starts at 8:30pm on Saturday (19 March).
They will be joining thousands of London residents and offices to mark Earth Hour, a campaign designed to raised awareness of the number of threats the planet faces from environmental issues such as climate change and deforestation.
The event, which is organised by WWF, is now in its ninth year, having started in Sydney in 2007. Around 178 countries are expected will take part, involving millions of people around the world.
On top of the London landmarks, hundreds others including Brandenburg Gate, Empire State Building, Sydney Opera House, Colosseum and Marina Bay Sands will be turning off their lights to mark the event.
Only non-essential lights are switched off, so most street lights will remain on.