The lights aren't on and everybody's home. It's a twist on the old cliché, but it will come true for millions on Saturday night, as the world celebrates Earth Hour. It's an environmental initiative backed by the World Wildlife Fund, designed to get everyone on the planet to turn off their lights for an hour between 8pm and 9pm.

The local leg of the event will start with a 6:45pm concert at Nathan Phillips Square featuring Nelly Furtado and the Philosopher Kings - acoustic, of course, to avoid using as little power as possible. After that, dozens of venues - including the CN Tower, the Rogers Centre and the Eaton Centre - will either dim their lights or turn them off entirely for the hour. (Some places aren't allowed to pull the plug entirely for safety reasons.)

It may not do much to change the climate by itself, but it's a symbolic gesture that can figuratively light the way. "This is just a point in time on Saturday, March 29th, turn off your lights for one hour between 8 and 9pm to show the world, to show your politicians, to show your friends and neighbours that you care about the planet," explains the WWF's Julia Langer.

More than a million homes in Ontario are expected to participate, making us the country's most committed province to the hour-long event. But this begs the question: what will happen to the energy grid when all those homes flick their lights back on?

"When people turn their lights back on, electricity has still been flowing through the grid. Just not as heavily. So when people turn them back on, there will not be a surge," explained Toronto Hydro's Denise Atallah.

Earth Hour began in Sydney, Australia last year to create awareness of climate change and immediately created an electrical charge of enthusiasm across that country when 2.2 million people joined in. It's since been picked up by advocates in 8 other nations and about 150 cities around the world - including Toronto, Ottawa, Montreal and Vancouver.

"This is very much focused as symbolic awareness-raising and sending a message to people in government and corporations who are making the big decisions that Canadians are concerned," explains the Fund's Keith Stewart. "They want action but the thing we hear a lot from sort of the powers-that-be is that, well, people say they're concerned but will they do anything? And this is a lot of people doing something at the same time."

But if it won't really save that much energy, why do it? "It's about ... partially thinking about how we use energy and when the lights go back on, maybe doing a few things differently in your own life."

Which is how turning off the lights can wind up shining a spotlight on a growing and urgent problem.

If you plan on keeping your home lit with candles for those 60 minutes, firefighters strongly urge using flashlights instead. They're less of a fire hazard.

A Saturday night isn't the busiest time for malls, government buildings or schools, but many of these institutions are powering down anyway, in a show of solidarity that is mostly symbolic.

Starbucks, Shoppers Drug Mart, and McDonald's are cutting lights at their head offices, but stores will remain open.

The Eaton Centre is one of many downtown landmarks turning off for the planet.

Others include:

CN Tower

Fairmont Royal York Hotel

Honest Ed's

Yonge Dundas Square and surrounding signage

Ontario Science Centre

Rogers Centre

Bata Shoe Museum

City Hall

Ryerson University and the University of Toronto

Staples and A&P stores (including Dominion, Ultra Food & Drug, The Barn, And Loeb) will dim existing lights.

The usual suspects are also taking part, like Grassroots Environmental Products, The Big Carrot and Whole Foods.

Clear Channel Outdoor will turn off 13 of its signs along the Gardiner Expressway