A. No matter what the packaging says about how many hours the bulb will shine, most CFL makers only warranty their bulbs for a certain time after date of purchase, typically two years. Defective bulbs generally fail within the first few months. Beyond that, premature burnout is likely caused by the way you're using the bulb. Putting it in a recessed can or an enclosed glass shade, for instance, will overheat a CFL not specifically designed for those fixtures. Using one in a lamp that gets switched on and off a dozen times a day also causes early death. To get a replacement, bring the bum bulb and your receipt back to the retailer, or get return-by-mail instructions on the manufacturer's website. One of your fellow readers, Nora Galambos of Stony Brook, New York, goes a step further by writing the date she installs the bulb in permanent marker on the ballast. She's already gotten her money back from The Home Depot for two duds.