Lights out in San Francisco, L.A. on Saturday

Mom always told me to turn off the lights when I left the room. Don't know if she was being environmentally conscious or didn't want a fat electric bill. Either way, the habit stuck.

This weekend, San Francisco aims to do one better than my mom and turn off all the lights in the city, for one hour at least.

Lights Out SF is "a citywide energy conservation event" on Saturday, during which the city's 700,000 residents are encouraged to turn off their lights between 8 and 9 p.m.

The group estimates that just one dark hour could cut about 15 percent of the energy used on a typical Saturday night.

Further down the coast, Los Angeles is encouraging the Hollywood glitterati to chill their shine this weekend. Lights Out LA also is scheduled for Saturday from 8 to 9 p.m. The same supporters are behind the coordinated efforts.

These actions are inspired by Sydney, Australia's Earth Hour. From 7:30 p.m. to 8:30 p.m. on March 31, 2007, more than 2 million Aussies turned off their lights. That caused a 10.2 percent drop in energy use.

The Down-Under results were pretty impressive. Businesses joined in the act too, and 90 McDonalds shut off their usually golden arches around town. Even the iconic Sydney Harbor Bridge had its lights out for an hour.

Some critique these efforts as just stunts, not sustainable habits. But like mom nagging me to turn off the light when I left a room, maybe seeing big cities go dark for an hour will remind us to turn off non-essential appliances and swap out old bulbs for efficient compact fluorescents ongoing.

Mom will be proud!