Lights will be switched off yesterday at 8 p.m. in 24 global cities, including Atlanta, Bangkok, Bogota, Chicago, Dublin, Montreal, Manilla, San Francisco, Sydney, Tel Aviv and more. This year's "Earth Hour" was an expansion of the event which took place last year in Sydney, Australia on March 31. A somewhat similar "Lights Out" was held in San Francisco in October last year, but this year it has been moved to coincide with Earth Hour last night.

Businesses, communities and individuals were encouraged to turn off the lights, as well as devices and machinery which use electricity or fossil fuels. Last night’s Earth Hour is an initiative of the World Wildlife Fund International.

Google also participated by turning its webpage black. The search engine switched its entire homepage color scheme and posted a simple message below its search box: "We've turned the lights out. Now it's your turn."

In the United States, it was apparently Chicago which dimmed the most between 8 and 9 p.m. last night. Its landmarks including the Sears Tower, Wrigley Building, John Hancock Building, The Loop theater district, the popular Navy Pier Ferris Wheel as well as many businesses dimmed or turned off their lights. Some bars and clubs held "green" themed parties celebrating the hour.

Officials estimated the hour-long outage lowered consumption by about 5 percent for the hour, compared with the Saturday before, the Chicago Tribune reports.

"It is about simple changes that will collectively make a difference – from businesses turning off their lights when their offices are empty, to households turning off appliances rather than leaving them on standby," claims the Earth Hour website.