The incandescent lightbulbs you've been twisting nonchalantly into your table lamps, wall sconces, and ceiling fixtures for all these years require lots of energy to produce a warm glow. And that's a problem, because electricity generation is one of the major sources of greenhouse gases.

Much of the energy used to light up our homes is provided by power plants that burn fossil fuels, and the quantity of greenhouse gases emitted by those plants is so vast that if every American household replaced just one incandescent with a compact fluorescent, we could prevent emissions equivalent to the annual output of more than 800,000 cars. But while switching to compact fluorescent lamps, or CFLs, significantly reduces your energy needs, you can take your planet-preserving efforts one step further by installing energy-efficient light fixtures as well.

According to Energy Star, replacing the five most frequently used fixtures in your home can save you nearly $60 in energy costs every year. Energy Star-qualified fixtures provide the same amount of light as traditional ones, but they use 75 percent less energy, and the bulbs that fit into them are made to last at least 10,000 hours (the average incandescent bulb lasts about 750 hours). In addition, these fixture-and-bulb combinations generate 78 percent less heat than standard ones, which means cooler rooms in warmer months and a lower utility bill to boot.

Do the light thing: the energy-efficient difference
The socket in a standard light fixture will accommodate either a screw-in incandescent bulb or a screw-in CFL, which incorporates in its base a voltage regulator known as a ballast. The ballast supplies the initial jolt of electricity the CFL needs to begin glowing, then regulates the power to ensure that the bulb emits the right amount of light. Without a ballast to control the flow of electricity, the light would steadily intensify until the bulb stopped working.

Energy-efficient fixtures, on the other hand, are sold as a package deal. Each fixture comes with one or more replaceable bulbs that fit into a pin-based socket. The ballast may be part of the fixture itself, rather than part of the bulb (in this regard, some energy-efficient fixtures are more like the fixtures for traditional straight-tube fluorescents). Once the bulb dies, you simply swap in a compatible bulb. Dedicated two- and four-pin systems are more energy-saving in part because the design makes it impossible for users to revert back to incandescents.

Generally speaking, energy-efficient residential light fixtures come in two types: the four-pin base and the two-pin GU-24, which operates at the same voltage as a standard electrical outlet (120 volts). Because GU-24 bulbs, like screw-in CFLs, incorporate their own ballast, you can easily replace them with bulbs of any wattage. Four-pin sockets, on the other hand, require you to purchase a replacement bulb of the same wattage, because the ballast is built into the fixture, and the bulb and the ballast have to match.

According to Paul Vrabel, director of the energy-efficient products group at lighting manufacturer Sea Gull Lighting, fixture makers are gradually switching to the GU-24 base in preparation for the wider release of bulbs that rely on an even more efficient technology: the light-emitting diode (LED). LED bulbs using the GU-24 base may eventually bypass CFL fixtures, but the light quality of LEDs has yet to be perfected. "I think that for a number of years, people will still be using CFLs," says Vrabel. "They will use both types-the GU-24s and the multi-pin-based CFLs-but the fixture manufacturers are gravitating to the GU-24 because of ease of replacement of lamps and ballasts."

Another factor to consider is the bulb's color temperature, which indicates the warmth or coolness of its light output (not of the bulb itself). Fluorescent bulbs come in various color temperatures, measured in degrees Kelvin: 2,700K, 3,000K, 3,500K, and so on. The lower the temperature, the warmer the light output. To get the flattering glow of an incandescent, look for a measure of 2,700K-the most popular option for pin-based lamps. For a cool, daylight equivalent, toss a bulb of 5,000K or higher into your shopping cart.

Also, if you're hoping to use your fixture in cold climates, check with the manufacturer for any restrictions on outdoor use. An energy-efficient fixture is generally more expensive, but it's an investment that will eventually pay for itself in lower utility costs and fewer trips to buy replacement bulbs. What's more, every Energy Star-qualified fixture comes with a two-year warranty.

What's in store: your shopping options
So you've mapped out the five (or more) light fixtures that you want to replace. The next step is to head to any home-appliance store or lighting showroom to browse through and select from the myriad options. If you're handy, you can usually install the fixture on your own (though be sure to follow the manufacturer's instructions). If you aren't comfortable working with electrical wiring, hire an electrician or visit a lighting showroom for professional installation. Note that if you're shopping for a fixture with a dimmer, you'll also need to purchase bulbs clearly specified by the manufacturer as dimmable. Dimmable CFL fixtures and bulbs are not yet widely available.

Most major lighting manufacturers make energy-efficient fixtures for every room in your home and in every decorative style. Portable fixtures, such as desk and floor lamps, plug into wall outlets, while hard-wired fixtures-including chandeliers, recessed overheads, and outdoor floodlights-are attached to the ceiling or wall. Check out the Lighting section on the Energy Star website to view examples of qualified fixtures, then search through the Energy Star Partner List for product manufacturers by country and state. To date, Energy Star has approved more than 10,000 energy-efficient fixtures.

When you do need to replace a bulb, you'll find that almost every home-improvement store, lighting showroom, and manufacturer website carries pin-based lamps. If you have a GU-24 base and you're unhappy with the light output, simply locate the appropriate type for your fixture and then search for a color temperature more to your liking. For standard four-pin bases, remember that you must match the bulb wattage to that of your fixture. Vrabel explains that the wattage of a CFL can be compared to that of an incandescent bulb on roughly a 1-to-4 basis. In other words, a 25-watt CFL will provide the same amount of light as a 100-watt incandescent.

If you're not quite ready to make the switch, Energy Star suggests that putting a screw-in spiral CFL in a standard fixture will provide the same level of energy savings as an energy-efficient fixture. However, pin-based CFLs are required to last 3,000 hours longer than spiral-tube screw-ins.

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