As a way to cut energy use, it could not be simpler. Unscrew a light bulb that uses a lot of electricity and replace it with one that uses much less.

While it sounds like a promising idea, it turns out that the long-lasting, swirl-shaped light bulbs known as compact fluorescent lamps are to the nation’s energy problem what vegetables are to its obesity epidemic: a near perfect answer, if only Americans could be persuaded to swallow them.

But now Wal-Mart Stores, the giant discount retailer, is determined to push them into at least 100 million homes. And its ambitions extend even further, spurred by a sweeping commitment from its chief executive, H. Lee Scott Jr., to reduce energy use across the country, a move that could also improve Wal-Mart’s appeal to the more affluent consumers the chain must win over to keep growing in the United States.

“The environment,” Mr. Scott said, “is begging for the Wal-Mart business model.”

It is the environmental movement’s dream: America’s biggest company, legendary for its salesmanship and influence with suppliers, encouraging 200 million shoppers to save energy.