The Environmental Working Group, a watchdog organization that is extremely diligent though sometimes a bit cranky, has shed some new and unflattering light on compact fluorescent bulbs.It seems that not all of these oddly shaped, eco-friendly fixtures are created equal when it comes to energy efficiency and safety. The group issued a report just after the New Year that lays out some the issues it has with CFLs and the Energy Star tag that virtually all of then carry. The report is timely. In the third quarter of last year, one of every four bulbs sold in the U.S. was a CFL, a new high, according to the EWG. These bulbs use about 75% less energy and last up to 10 times longer than conventional bulbs, more than making up for their higher upfront cost. The EWG's beef is these bulbs vary more widely than you might imagine in their lifespan and mercury content. The group argues that Energy Star should reserve its stamp of approval for only the brightest bulbs in the pack; otherwise it doesn't mean much. Of course, even laggard CFLs are an improvement over conventional bulbs, which is no doubt how they earn the Energy Star seal. But when you learn that the lifespan for these bulbs can range from 6,000 hours (the Energy Star minimum) to 15,000, as the report points out, you understand that it pays to pick your bulbs more carefully than you had previously. The group lists seven winning CFLs (it calls them the magnificent seven for their long life and low mercury content). Several are somewhat obscure and available on niche lighting or eco Web sites, but a few are sold on Amazon.com ( AMZN).