Long-lasting CFLs are ideal for hard-to-reach spots or areas where lights are on for long periods. But unlike incandescent bulbs, which reach full brightness instantly, CFLs took from 27 seconds to 3 minutes to fully brighten in our tests. Spirals are the quickest; floodlights and covered outdoor bulbs, the slowest. Don't use CFLs in staircases, areas where you need instant light, or in lamps that children could tip over easily and break the bulb. Then consider these tips:
They tell you how much light the bulb provides. Watts tell you how much electricity it uses. Both are listed on the package. Look for one with comparable lumens to the bulb you're replacing. Our tests found that some CFLs are slightly dimmer than comparable incandescent bulbs and continue to dim as used. Manufacturers suggest replacing a 60-watt incandescent with a 13- to 15-watt CFL, a 4:1 ratio. But if the CFLs you've tried weren't bright enough, Rensselaer Polytechnic Institute's Lighting Research Center in Troy, N.Y., suggests using a 3:1 ratio instead; that's a 20-watt CFL to replace a 60-watt incandescent.
The yellowness, blueness, or whiteness of a bulb's light is measured by its temperature, in kelvins. CFLs with a 2700 K are closest to the yellowish light of a soft-white incandescent. Those at 3000 K are similar to the whiter light of halogen bulbs. At 3500 K to 4100 K, bulbs emit a cool, bright white that works well in kitchens and work spaces; 5000 K to 6500 K CFLs mimic daylight and are good for reading. If you're using CFLs and incandescent lights in one room, or even CFLs from different brands, stay within 200 K to minimize noticeable color differences among bulbs.
The accuracy of how colors look under the light is measured by the Color Rendering Index, which ranges from 0 to 100. The higher the CRI, the more accurate the colors. Incandescent bulbs and sunlight score near 100.