Several major Chinese websites will "go dark" in observation of Earth Hour this Saturday night, as homes and businesses around the world turn off lights for an hour to promote energy conservation.

It's an idea developed by BBH China for World Wildlife Fund China. Johnny Tan, BBH China's executive creative director, said the project stemmed from a desire to get more people participating in Earth Hour and the larger Earth Week campaign.

"We want to make sure we give people a great experience and make them feel like they're part of something," he said. "We want this to be purposeful and not just a gimmicky thing."

The campaign involves some of China's most popular websites: social networking sites Renren, Ushi and Kaixin; video site Youku; instant messaging service QQ and email portal 139.

From 8:30 p.m. to 9:30 p.m., the sites will be dark, except for a spotlight guiding users across the page. The message "light only what you need" will appear on the screen.

"We hope BBH's creative helps the users to better understand the cause, to use only what we need and to take the movement 'beyond the hour' to make a real difference," Allen Chai, manager of WWF China Earth Hour, said in a statement.

Mr. Tan said the technical coding work needed to implement the idea was easy. A bigger challenge was helping a few sites overcome reluctance about participating over worries that the blackout would negatively impact user experience.

"Energy saving is still not in most Chinese daily life. By joining this great initiative, we hope to raise not only the awareness, but more importantly, to turn that awareness into real actions," Renren VP Jing Huang said in a statement.

If the campaign in China is a success, then plans are to have websites around the world participating next year, Mr. Tan said. BBH company websites will also observe the digital blackout on Saturday night.