Wal-Mart Stores Inc. (WMT) reached an annual target of selling 100 million energy-efficient light bulbs ahead of schedule after heavily marketing them as a way for consumers to save money and fight global warming, the retailer said Tuesday.

The world's largest retailer set the target, which roughly doubled its previous annual sales, late last year as part of a series of green policies. It expanded shelf space, cut prices and ran ads for the swirly compact fluorescent bulbs, or CFLs.

Environmentalists and manufacturers said Wal-Mart's push has helped boost national demand for the efficient bulbs.

Backers including the U.S. Environmental Protection Agency say CFLs use one-third the energy of a traditional incandescent bulb, last up to 10 times longer and save $30 or more in energy costs over their lifetime.

Last year, an estimated 150 million CFLs were sold nationally, and the number may be twice that this year thanks to Wal-Mart's contribution, said Noah Horowitz, senior scientist with the Natural Resources Defense Council.

Less than 10 percent of light sockets in North America have a CFL rather than a traditional bulb, up from two percent three years ago, according to manufacturer Philips Lighting, a division of Royal Philips Electronics NV (PHG).

Wal-Mart's executive in charge of environmental strategy, Andrew Ruben, said the 100 millionth CFL was sold over the weekend at one of Wal-Mart's roughly 4,000 U.S. stores and Sam's Clubs.

Wal-Mart achieved the target by raising awareness of CFLs and lowering prices, Ruben said.

Wal-Mart worked with suppliers to reduce CFL prices by about half, to around $1.65 per for the equivalent of a 60-watt incandescent bulb from around $2.40 a year ago. That compares to about 24 cents for the incandescent bulb.

It raised awareness by expanding shelf space for CFLs as well as promoting them in-store, in ads and through campaigns with other groups.

Wal-Mart has not yet set a new target for CFL sales.