Duke Energy, Charlotte, N.C., is offering coupons for energy-efficient compact fluorescent lamps (CFLs) to its customers in North Carolina and South Carolina to help them save money on their electricity bills and reduce the need for additional power plants.

The utility will mail customers a coupon, redeemable at Walmart, good for a free six-pack of 13-watt CFLs, which typically have the lighting output equivalent to traditional 60-watt incandescent lamps. The six CFLs collectively can save customers up to $180 on their electricity bills over their expected lifetime. According to Duke, if all 1.3 million customers who receive the coupons redeem them and replace existing incandescent lamps with the new CFLs, the amount of electricity saved over the lifetime of the lamps would be enough to power more than 36,000 homes.

“Sustained energy-efficiency efforts can be one of the most environmentally friendly ways to meet our customers’ electricity needs and is often less expensive than building power plants,” said Gianna Manes, Duke Energy’s senior vice president for retail customer products and services. “Energy efficiency also can help our customers save money on their overall energy costs.”

CFL coupons were mailed in March and April.