Although they contain small amounts of mercury, compact fluorescent lightbulbs (CFLs) can actually reduce net emissions of the toxic heavy metal, a new study by researchers at Yale University has found. Because incandescent bulbs use four times as much electricity as CFLs, and because coal-fired power plants spew thousands of tons of mercury, switching to compact fluorescents would cut overall mercury pollution in coal-dependent countries such as China and some eastern European nations. If the U.S. switched entirely to compact fluorescent bulbs, it would avoid about 25,000 metric tons of mercury per year, the researchers calculated. Regions that don’t burn coal — such as California — would see an increase in mercury pollution, however, unless they boost recycling of CFLs or find energy-efficient bulbs that are less toxic. “If we want to be truly sustainable, we can’t be dependent on materials that use toxic substances,” said Julie Zimmerman, the study’s coauthor.