Lightbulb buying guide

When replacing a bulb, choose a new one that's the same size or smaller to be sure it fits the fixture. Dimmers require dimmable bulbs and lights used outdoors must be designed for exterior use. Our Ratings indicate manufacturer-recommended uses; also check the bulb package for details.

Select bulbs that provide the desired brightness at the lowest wattage (watts indicate energy use). Brightness is measured in lumens. When buying CFLs and LEDs known as A-type for their bulbous shape--the kind used in lamps and other fixtures--look for at least 450 lumens if you're replacing a 40-watt bulb; 800 lumens or more for a 60-watt bulb; at least 1,100 lumens for a 75-watt bulb; and 1,600 lumens or higher when replacing a 100-watt bulb. For R30 floodlights, look for at least 10 times the watts of the bulb you're replacing, 650 lumens to replace a 65-watt bulb, for example.

Warm lighting is flattering and used in most home applications, so the Kelvin temperature is in the lower end of the range. Standard incandescent bulbs produce a warm yellowish light and have a color temperature of about 2700 Kelvin (K). If you like that warm color, look for CFLs and LEDs with about 2700K. At 3000K, the light is whiter and comparable to a halogen's. For a cool, bright white light, look for bulbs in the 3500K to 4100K. And 5000K to 6500K bulbs mimic natural light or daylight.

The Color Rendering Index, or CRI, tells you how accurately colors appear under the bulb's light. The CRI ranges from 0 to 100 with daytime sunlight at 100 and incandescent bulbs right around that. A CRI of at least 80 is generally recommended for interior lights, and differences of fewer than five points are insignificant. To compare bulbs, look at the CRI of bulbs with the same Kelvin temperature.

They're inexpensive and instantly emit a warm light in all directions, accurately revealing the colors of objects and skin tones.

They use significantly more electricity than energy-saving bulbs and most only last about 1,000 hours.

They use about 75 percent less energy and last 7 to 10 times longer than the incandescent bulbs they replace. Typically it takes less than a year to recoup the cost of most CFLs. The spirals and covered spirals give off light in all directions, making them a good choice for lamps, and the flood/reflector bulbs are more directional. Several CFL brands offer bulbs with a plastic coating that contains the mercury and any shards if the bulb breaks.

They take time to fully brighten, typically from 19 seconds for spiral bulbs to several minutes or more for flood/reflector bulbs, especially when used outdoors in frigid temperatures. Most CFLs aren't dimmable, and since frequently turning them on and off affects the bulbs' performance and life, they shouldn't be used in certain sockets. CFLs contain mercury and while the amount is small and has decreased substantially in the bulbs we tested, they should be recycled. This prevents mercury from being released into the environment when the bulbs break in the trash or as landfill. If a CFL breaks at home, follow the clean-up tips from the Environmental Protection Agency at www.epa.gov/cfl/cflcleanup.html.

Halogens are incandescent bulbs that use about 25 to 30 percent less energy than standard incandescents. The halogen bulbs meet the new energy-efficiency standards required by federal law and will not be phased out with standard incandescent bulbs. Halogen bulbs instantly produce light and are fully dimmable. The A-type bulbs cast light in all directions and accurately reveal the color of furnishings.

Some do not last much longer than standard incandescent bulbs yet cost more.

They use slightly less energy than CFLs and manufacturers claim LEDs last 20,000 to 50,000 hours. That's about 18 to 46 years when used three hours a day. LEDs instantly brighten, even in frigid temperatures, and performance is not affected by frequently turning them on and off. Some LEDs we tested dim as low as incandescent bulbs.

Among A-type bulbs, the type used for lamps and other applications, not all LEDs are good at emitting light in all directions. The shapes are unusual and the bulbs are heavier. And LEDs can be expensive although prices have been going down. As prices drop, so will payback time.

Dimmers require dimmable bulbs. Most of the CFLs we tested are not. Some LEDs are and can dim as low as incandescent bulbs. The Ratings indicate which bulbs are dimmable; you can also find that information on the bulb package.

Not every CFL or LED can be used in every type of light fixture so check the information on the package before buying one for a specific application. For example, not all CFLs and LEDs are intended for use in ceiling fans in which the bulb hangs down. You can, however, use newer bulbs in some vintage fixtures. For example, you can replace a 60-watt incandescent with a 13 to 15 watt CFL.

As of January 2012, a Lighting Facts label must appear on the packages of most lightbulbs. It will show brightness, energy use, estimated energy costs, expected life, light color in kelvins, and, for CFLs, the fact that the bulb contains mercury.

Some CFLs and LEDs we tested can be used in fully enclosed fixtures, according to the manufacturers. Look for this information on the lightbulb package. It's important to note as heat build-up can be a problem in enclosed fixtures and can shorten the life of CFLs and LEDs. The Ratings state which bulbs can be used in these fixtures, based on manufacturers' recommendations.

Many of the tested CFLs and LEDs work outdoors but cannot get wet, so they need to be protected from direct contact with rain or snow. The Ratings indicate which bulbs can be used in this way.

Known also as vacancy sensors, motion sensors automatically shut off lights after a person leaves a room or, when used outdoors, turn on lights when movement occurs near the light fixture. The bulb and motion sensor must be compatible to work properly. Check with the manufacturer of the motion sensor and read the bulb packaging to be sure.

Using a bulb that works with a photocell is another way to save energy. The photocell turns off lights when daylight appears and turns them back on when darkness falls. But the photocell may be incompatible with your bulb, and might shorten the bulb's life. Check with the photocell manufacturer and read the bulb packaging for compatibility.

In short, because they waste energy. Less than 10 percent of the energy used by the bulb produces light; the rest escapes as heat. So it takes a lot of energy to create the incandescent's warm glow. There are an estimated 6 billion lightbulbs in American homes, according to the Department of Energy, and more than 3.6 billion are standard incandescent lightbulbs. You can see how all this wasted energy adds up.

The Energy Independence and Security Act of 2007 aims to help the country become more energy independent, in part, by increasing the efficiency of vehicles, buildings, commercial and industrial equipment, and consumer products such as residential dishwashers, washers, dehumidifiers, and lightbulbs. Most screw-in based bulbs are required to use at least 27 percent less energy by 2014. CFLs, LEDs and some halogen bulbs meet the standard, traditional incandescents do not.

So on January 1, 2012 the phase out began with 100-watt incandescent bulbs, which can no longer be made or imported but can be sold until supplies run out. The 75-watt fades away in 2013, and a year later it's goodbye to 60- and 40-watt incandescent bulbs. California began its phase out in January 2011; Europe and Australia in 2009. To find the right energy-saving bulbs for your sockets, see our Ratings of CFLs, LEDs and halogen bulbs.

Energy Star-qualified 60-watt replacement CFLs are as bright as regular incandescents, use about 75 percent less energy, and last seven to 10 times longer. Of course, they need time to fully brighten, and most aren't dimmable. Our tests of 100-watt-equivalent CFLs found that they may sacrifice some brightness to save energy.

CFLs save money. Fans of 100-watt incandescents like their added brightness. But when compared with a 100-watt incandescent, a CFL can save you $100 or more on electricity over the lifetime of the lightbulb. All bulbs lose brightness over time, including old-fashioned incandescents. But in our tests of 100-watt replacement CFLs, even the brightest were only roughly 1,400 lumens after 3,000 hours of testing. Energy Star recommends 1,600 lumens or more to replace a 100-watt bulb when new, although it allows lumens to drop off as CFLs age.

Keep in mind that the 100-watt equivalent CFLs we tested provide substantially more light than the 60-watt CFL replacements in our labs. So if you're just looking for more light than a 60-watt bulb, any of the recommended 100-watt replacement CFLs should be fine. They all provide a warm, yellow light but are slightly larger than the incandescents they replace.

CFLs contain a small amount of mercury and should be recycled at the end of their useful life. Home Depot, Lowe's and Ikea, among others, accept used bulbs for recycling.

When a CFL shatters, the cleanup involves a series of steps to minimize exposure to mercury. The U.S. Environmental Protection Agency offers step-by-step cleanup advice. To prevent such breakage, don't put CFLs in lamps in play spaces or other areas where light fixtures can be easily broken or knocked over.

LEDs instantly brighten and aren't affected by frequent on/off cycles and cold temperatures, and many can be dimmed. They use slightly less energy than CFLs and are claimed to last even longer, 20,000 to 50,000 hours, or around 20 to 40 years. LED prices are dropping, but the bulbs are still expensive and have a longer payback period. Not all lamp-type LEDs emit light evenly so look for Energy-Star qualified bulbs.

LED's are pricey because production is challenging and expensive, but as with other electronic-based products, prices are dropping as demand and performance go up. Until then, look online for rebates from manufacturers and utilities. You'll spend about $1 a year on average to power an Energy Star LED or CFL, $3.50 for a halogen, and almost $5 for a traditional incandescent bulb, according to the Department of Energy.

Semiconductor chips and electronic circuitry in LEDs can include lead, arsenic, and gallium, but those substances aren't accessible, even if the bulb breaks. LEDs should be recycled with other electronic waste.

Some halogens use about 25 to 30 percent less energy than standard incandescents, but they cost more and many don't last much longer. So you're unlikely to save much money. But halogens instantly produce light, are fully dimmable, and cast light evenly.

The Color Rendering Index of halogen bulbs is also higher than a CFL. The CRI measures how accurately the bulb displays colors. The 100-watt replacement halogens we tested use less energy than the incandescents but use significantly more than CFLs, and they don't last nearly as long. That short life span, similar to an incandescent's, is one reason halogens don't meet Energy Star standards.

Not every energy-saving lightbulb can be used in every fixture. In fact, incorrect use of an energy-saving bulb can affect its performance and shorten its life. Before buying a replacement bulb, check the package for proper use. Here are some tips on how to choose the right bulb for the fixtures in your home.

Lamps and ceiling fixtures: Make sure the bulb can be used in a fully enclosed fixture, if that's what you have. Consider covered CFLs if you don't like the spiral look, but those bulbs take longer to warm up.

Recessed or track lights: The interior color of the recessed can or track head affects brightness. Shiny metal and white interiors reflect light. Black absorbs some light, so you might want more lumens to compensate.

Outdoors: The colder the temperature the longer it will take for CFLs to brighten up. LEDs aren't affected by the cold. Bulbs in the 2,700- to 3,000-kelvin range flatter warm-colored exteriors; bulbs with 3,500 or more kelvins enhance grays and cool colors and can appear brighter.

Lumens: Brightness is measured in lumens; watts measure energy use. Here's a cheat sheet for equivalents: To replace a 40-watt incandescent lamp bulb, look for at least 450 lumens; 60 watts, get 800 lumens or higher; 75 watts, get a minimum of 1,100 lumens; 100 watts, get 1,600 lumens and up.

Kelvins: The color of the light is measured by its temperature in kelvins (K). To match a soft-white incandescent, get a CFL or LED with 2700 K. The light from bulbs with 3000 K is comparable to the whiter light of halogen bulbs, while bulbs with 3500 K to 4100 K give off a cool, bright white light. To mimic daylight, and for task lighting, choose bulbs with 5000 K to 6500 K but those higher temperatures, with their bluer tones, can be unflattering indoors. Rely on kelvins to get the right color light because terms like soft white and warm white mean different things to different manufacturers.

Color Rendering Index: The CRI ranges from 0 to 100 and indicates how accurately colors appear under the light. The higher the CRI, the better. Incandescent bulbs are about 100. Most CFLs we tested have a CRI in the low to mid 80s, though a few reached the upper 80s and lower 90s. A CRI of at least 80 is generally recommended for interior lights, and differences of fewer than five points are insignificant. Few of our staffers have complained about the CRI of the CFLs and LEDs we tested.

CFL and LED bulbs use fewer watts, or less energy, to produce the same amount of light, or lumens, as incandescent bulbs. But the color of the light varies by the type of bulb, so you need more information than just a bulb's watts to get the light you'd like. The Lighting Facts label, patterned on nutrition labels on foods, will give you much of that information. It lists the bulb's lumens, or brightness; its estimated yearly energy cost; how long the bulb is expected to last; its appearance, from warm to cool; how much energy, or watts, it uses; and whether the bulb contains mercury.

Yes. CFLs save money faster. It usually takes less than a year to recoup the cost of most CFLs, according to our tests, which are based on the bulbs being turned on for three hours a day. Each 60-watt equivalent CFL can save you about $60 over its lifetime. Each 100-watt equivalent can save you $100 or more over its lifetime in electrical costs.

LEDs take longer to start saving money, but because of its longer claimed life, an LED can save you $100 to $400 per bulb over its lifetime.

Yes. Light fixtures are designed to handle a bulb that uses a certain wattage. Because a CFL uses far fewer watts than a standard incandescent bulb while providing the same amount of light, you can replace a 60-watt incandescent with a 13- to 15-watt CFL without worrying about overheating the fixture. CFLs last much longer, so you won't need to replace them as often. That's handy if you have to remove a fragile or hard-to-replace cover from your vintage fixture to replace the bulb.

Because CFLs don't fully brighten instantly, don't use them in staircases or other areas where you need instant brightness. Consider halogen or LED bulbs instead.

Manufacturers of CFLs and LEDs make a lot of promises, from a bulb's brightness and light color, to its lifespan and energy savings. Our lighting lab puts those claims to the test, and after thousands of hours of testing, continually updates the results on our website. Our Ratings indicate payback time, or how long it takes for a bulb to pay for itself compared to the incandescent it replaces. After that point you're saving money by using less electricity.

For more information, see our lightbulb Ratings and recommendations (both are available to subscribers).