Tonight, millions of people worldwide will turn off their lights for an hour, to demonstrate their commitment to energy efficiency.

You can be one of them.

The second annual Earth Hour, an initiative of the World Wildlife Fund, occurs from 8:30 to 9:30 p.m. in each time zone, rolling west across the globe like the stroke of midnight on New Year’s Eve.

More than 2,700 cities in 84 countries have signed on to participate, but you can get involved no matter where you are. Just turn off all non-essential lighting at your home or business.

In Atlanta, which is one of the key U.S. cities for Earth Hour, more than 500 buildings will go at least partially dark at 8:30 p.m., including Philips Arena and the CNN Center.

Also participating is Georgia Power, which will dim the lights at its 24-story, 850,000-square-foot headquarters in downtown Atlanta.

Georgia Power spokeswoman Carol Boatright said it’s more than just a symbolic gesture. The utility company’s own data shows that Earth Hour did actually save energy in 2008.

“Last year during that hour, in Atlanta, we saw a decrease in electricity use of about 4 percent,” she said. “That’s equivalent to just over 7 megawatt-hours of electricity, enough to power more than 1,750 homes for that hour.”

Though Gainesville is not an official Earth Hour city, individual residents in and around Hall County will be flicking off their light switches.

“I’ve marked it on my calendar,” said Debbie Loveless of Gainesville. “We’ll be turning off our computers and anything else that’s drawing power.”

Loveless said her family is already conscientious about energy usage. But for people who’ve never thought much about the electricity they consume, Earth Hour could help them develop new habits.

“I hope people will expand this into looking at things they do every day,” Loveless said. “Unless we start taking action (on conserving the environment), we’re not going to leave much behind for our children and grandchildren.”

Loveless is also planning to attend a program Sunday afternoon at St. Paul United Methodist Church on Washington Street. Scheduled from 2 to 4 p.m., “Stewardship of the Earth: Why Should We Care?” will feature speakers from Georgia Interfaith Power & Light, a nonprofit organization that promotes awareness of conservation among churches.

The group will show a 35-minute documentary, “Kilowatt Ours,” and give practical tips for a more sustainable lifestyle.

Loveless said her family started making changes after attending a similar program at another Gainesville church last year.

“We recycle, we compost, we’ve changed out a lot of our light bulbs,” she said. “But there’s still so much I can learn.”