A. Bulbs that burn a filament, such as incandescents, provide the full spectrum of light, approximating sunshine and giving everything a natural glow. A CFL's spiral tube is filled with gas, which produces ultraviolet light that is, in turn, reflected into a room as white light by a phosphorous coating on the glass. That coating can distort colors and give skin a ghoulish hue. By altering the phosphor manufacturers have recently improved the quality of CFL light, as measured by the color rendering index. This gauges how accurately a bulb renders colors, from 0 to 100, with incandescents scoring a 100. Today's CFLs are in the 80s, which is good for ambient light. But they're still not great for task lighting. So keep incandescents in the bath, in the laundry where you need to do spot treating, and where you prep food in the kitchen. Replacing bulbs elsewhere in the house will still save you money.