Oh my, this one snuck up on me. I’d been meaning to post about it earlier. Hope it gets to you in time.
The idea is for everyone to turn off your lights tonight at 8:30 PM (your local time) for one hour as a gesture of solidarity for the environmental well-being of our planet.
All the details, including videos and Twitter hash tags, can be found on the Earth Hour website.
See you (or not see you, as the case may be) then. 
There`s a lot of amazing photos on the oficial site of Earth Hour, you link on it. Thanks.
P.S. In Russia there were 30 min turn off lights.