Just before 9 oclock, the meter at the Toronto Hydro control centre hit a low of 2,738 megawatts - 5 per cent below the demand an hour earlier and about 8.7 per cent less than a typical late March Saturday night.
The starting point was lower than usual in part because many buildings, including the CN Tower and the Stars offices at One Yonge St., shut their lights well before Earth Hours official start time.
Across the province, demand was down about 900 megawatts, or 5.2 per cent, said Terry Young, spokesperson for the Ontario Independent Electricity System Operator.
Across the downtown, while most street-level storefront signs remained on, business logos atop high-rise office towers and hotels were dark, and lights blinked out in many condo windows.
Staff at the Sheraton Centre hotel apologized because technical problems delayed their participation, but they vowed to keep the lights out until 10 oclock as compensation.
Mainly, though, Earth Hour was marked in darkened homes where families enjoyed candlelit dinners and games, or went outside to stargaze, and at events like the acoustic concert, headlined by Nelly Furtado, that thrilled a jammed throng at Nathan Phillips Square.
Many restaurants planned candlelit dinners and special menus, while activities ranged from glow-in-the-dark soccer to a torchlight parade.
Toronto was toward the end of Earth Hours global progression, which began 17 hours ago in Christchurch, New Zealand and Suva, Fiji.
Christchurch - where a crowd in a central square chanted a countdown similar to New Year's Eve - provided an impressive launch: Energy consumption dropped by 13.1 per cent, according to officials from World Wildlife Fund, which launched Earth Hour last year in a single city, Sydney, Australia, to raise awareness of climate change and inspire long-term action to reduce greenhouse gas emissions.
The final stops, two hours from now, will be Vancouver and San Francisco, where the lights are to go out on the Golden Gate Bridge.
Organizers expect that, by then, about 30 million people will have taken part in an event that far exceeded their hopes and, to their great delight, beyond their control.
More than 380 communities, including at least 150 across Canada, joined Earth Hour. About 300,000 individuals signed up on a WWF website that was overwhelmed during the past couple of days. That included 100,000 Canadians.
Earth Hour shows that everyday people are prepared to pull together to find a solution to climate change. It can be done, said James Leape of WWF International.
In Sydney, the event appeared to be at least as popular as last year, when 2.2 million people took part and electricity consumption fell by 10.2 per cent. This time, lights at the famous Opera House and Harbour Bridge were switched off and Australians held candle-lit beach parties, played poker by candle light and floated candles down rivers.
Australian energy officials said electricity consumption was down by 1,000 megawatts across the country, the equivalent of shutting down two large generating stations.
In Bangkok Thailand, some of the citys business districts, shopping malls and billboards went dark, although streetlights stayed on. One major hotel invited guests to dine by candlelight and reported brisk business.
Greece, an hour ahead of most of Europe, was the first on the continent to mark Earth Hour. On the isle of Aegina, near Athens, much of the population marched by candlelight to the port. Parts of Athens, including the floodlit city hall, also turned to black.
In Copenhagen, the Tivoli and the Royal Palace and the opera darkened for an hour, along with many streetlights.
In the central square a lot of people were standing looking at the stars, said Ida Thuesen, of WWF Denmark. Its not often you can see the stars in a city.
In Norway, at the Kvitfjell ski resort that was host of the 1994 Winter Olympic downhill, parties were held by candlelight as heavy snow fell outside.
In Britain, 26 town and city councils signed up to switch off non-essential lights, as did several historic buildings including Prince Charles private residence Highgrove House, as well as London City Hall, Winchester Cathedral and the Government Communication Headquarters radio monitoring station.
The town of Brighton turned off the lights on its pier and pavilion to mark the event.
Floodlights went out at landmarks in Budapest, including its castle, cathedral and parliament.
In Ireland, where environmentalists are part of the coalition government, lights-out orders went out for scores of government buildings, bridges and monuments in more than a dozen cities and towns.
Activists gathered outside one of Dublins most impressive floodlit buildings, the riverfront Custom House, and cheered as the lights went out. The building houses the Environment Department, run by a Green Party minister.
But next door, the international banks and brokerages of Dublins financial district blazed away with light, illuminating floor after empty floor of desks and idling computers.
The banks should have embraced this wholeheartedly and they didnt. But its a start. Maybe next year, said Cathy Flanagan, an organizer in Dublin.
Irelands more than 7,000 pubs elected not to take part - in part because of the risk that Saturday night revellers could end up smashing glasses, falling down stairs, or setting themselves on fire with candles.
Likewise, much of Europe - including France, Germany, Spain and European Union institutions - planned nothing to mark Earth Hour.
That didnt dismay organizers, who said theres a powerful message in the fact that the usual powerhouse countries arent leading the way, and that even in wealthy places like Canada its very much a grassroots phenomenon.
Im just beginning to get a sense that this is a way of giving voice to a lot of people who dont normally have a voice, Andy Ridley, of WWF in Sydney, said a day before the event.