What it means. Watts are probably what you think of when you replace a lightbulb around the house, be it an incandescent bulb or a compact fluorescent fixture. But lumens output is really the key factor in choosing a lightbulb for an application: Watts tell you how much electricity a bulb consumes whereas lumens represent bulb brightness and how much light they provide.

Manufacturers list lumens and wattage on bulb packages, so look for a comparable lumens output at the lowest wattage when you're replacing a bulb. A 13-watt CFL provides around 800 lumens, about the same as a 60-watt incandescent bulb. (The image, courtesy of Philips, shows a residence in Mexixo City with an LED installation by Grupo G1-V3.)

Why the buzz? We're in the midst of a lighting revolution, as manufacturers continue to improve their compact fluorescent lights and do R&D on LEDs. LEDs are being hailed as the next big thing because they're highly efficient, last a long time (up to 100,000 hours, claim some makers), and lack the mercury that all CFLs contain. The New York Times recently covered the growing interest in and use of LEDs in "Green Promise Seen in Switch to LED Lighting."

But further research is still need needed to realize the full energy and cost savings of LEDs and to make bulbs that will work in more residential applications, say the experts at the Lighting Research Center at Rensselaer Polytechnic Institute, in Troy, New York. (So far, we've tested LEDs only for undercabinet lighting.) What's more, LEDs cost $20 to $100 each, a lot more than CFLs.

Until LEDs become more widely available for home use and come down in price, replacing incandescent bulbs with CFLs is your best energy-saving move. Buy Energy Star-qualified CFLs, and be sure to consider the color of the light. The color could affect how bright a light appears, even if lumens are the same, according to the U.S. Department of Energy.

Incandescent lights have a soft, yellowish glow, but CFLs nearer to the color of daylight aren't as yellow and might appear brighter.

Keep in mind that the lower the Kelvin number listed on the package, the yellower the light; higher numbers indicate bluer or whiter light. Watch this New York Times video, featuring Home Editor Bob Markovich, to learn more about the different types of CFLs.—Kimberly Janeway | e-mail | Twitter | Forums | Facebook

Essential information: Watch our video on safety issues and CFLs.