Compact fluorescent lightbulb (CFL) package with energy Star logo. Household compact fluorescent light bulbs with the E26 Edison screw base that fit into existing light fixtures are becoming increasingly popular in recent years. Compared to incandescent light bulbs, CFLs are generally several times more efficient and have a longer rated life. Despite the improved efficiency, the actual environmental effect of CFLs is the subject of much debate because they typically use mercury vapor.