A. All that's inside an incandescent bulb is a glowing wire filament. The gas-filled tube of a CFL isn't as easy to squeeze into a petite package. The higher the wattage, the more gas and the bigger the spiral. That 27-watt bulb of yours compares with a 100-watt incandescent. But thanks to new, smaller plastic ballasts, the section above the screw base that houses the bulb's circuitry, manufacturers are now making CFLs in standard incandescent sizes. Before you shop for a new CFL, measure the length of the bulb you're replacing, and bring a ruler to the store. Many online sellers also list dimensions on their websites.