CHICAGO (CBS) — Several Chicago area landmarks will go dark Saturday night for at least an hour as Illinois takes part in Earth Hour.

Earth Hour is an international effort by the World Wildlife Fund to show a commitment to preserving energy.

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Earth Hour will begin at 8:30 p.m. and run for 60 minutes.

ComEd spokeswoman Krissy Posey says the event is meant to be symbolic

“It’s just a start to maybe going beyond the hour to find ways that you can save energy throughout the year,” Posey said.

The Merchandise Mart will be the first landmark to go dark. Other buildings and landmarks that will participate including Navy Pier, the Willis Tower, City Hall, the Wrigley Building and Trump Tower.

This is the fourth year for the event, and Posey said she believes ComEd customers are getting the message

“Our customers like to save money, so they realize that one way to do so is managing their energy usage,” Posey said.

More than 133 countries and thousands of cities are participating in the observance.