The third annual Earth Hour is March 26, 8:30pm, worldwide. Millions of participants will switch off lights and electricity for one hour, in a global pause for conserving energy and exploring modern lifestyle alternatives.
L.A.'s chapter of Earth Hour has its own page: http://www.meetup.com/Earth-Hour-Global/Los-Angeles-CA/
Users can even design their very own unique lightswitch and share it on Facebook.
To organize your own Earth Hour party or event, check out their "How To" guides: http://www.earthhour.org/howto/Guides.aspx