Thomas Edison, who invented the incandescent light bulb, was born this day in 1847. Today, his invention is being replaced by compact fluorescent bulbs that use less electricity and last much longer. That's where knowledge of these wonder bulbs ends for many of us. If you buy them by wattage -- as we're used to doing -- you might wind up a bit light on light. Package guidelines say a 13-watt cfl equals a 60-watt bulb. But if you're over 50, you might be disappointed because older eyes take in only half as much light as they used to. Instead, buy 25 percent more lumens than the incandescent you're replacing. If it's a 60-watter, with 870 lumens, buy a cfl with 1,050 lumens for "equality." To make it last longer, avoid frequent ons and offs -- one hour or more at a time is best. Also, avoid excessive vibration such as placement near doors that slam shut and high-humidity levels. Both shorten the life of compact fluorescent bulbs.