Say you want to buy the most eco-friendly lightbulb. Energy-saving compact fluorescents seem like a good choice, but which one is best? Is one manufacturer more environmentally responsible than another? The answer is probably yes, and new product labels will soon make such comparisons easy for shoppers. Gregory Norris, an industrial ecologist at Harvard University, has developed an open-source database called Earthster that evaluates products based on the raw materials used and the emissions generated. As a major funder of the project, Wal-Mart will be one of the first retailers to roll out the new system.