How much light do you want? The brightness of a bulb is measured in lumens. If you're used to comparing bulbs by their wattage, the U.S. Department of Energy offers simple guidelines for choosing a bulb with the right number of lumens. To replace a 40-watt incandescent, look for a bulb with about 450 lumens. To replace a 60-watt bulb, aim for 800 lumens. A 75-watt equivalent should have about 1,100 lumens, and a 100-watt equivalent about 1,600. These numbers are only averages, so you can choose a bulb with more lumens if you want brighter light or a lower-lumen bulb for dimmer light.
What kind of light fixture do you have? Not every bulb will work in every fixture. Some CFLs and LEDs, for instance, can't be used in ceiling fixtures where the bulb hangs upside down. Other bulbs can't be used in a fully enclosed fixture or in an outdoor fixture that's exposed to the elements. Check the package to make sure the bulb you choose is rated for your intended use. Also, check the size and shape of the bulb to make sure it will fit in your fixture. If you're using a light fixture in which the bulbs are visible, such as a ceiling fan, you may prefer the smoother look of a traditional rounded bulb, rather than a spiral-type CFL or a flattened LED. For recessed can lights, floodlights or reflector-type bulbs are your best bet; they're designed to direct the light out of the fixture and disperse the heat that can build up inside.
Where will the bulb be used? CFLs tend to wear out faster when they're switched on and off frequently, so they're not great options for bathrooms or closets, which are usually lit for only a few minutes at a time. CFLs also take anywhere from a few seconds to a few minutes to reach their full brightness when you turn them on. In any area where you need full brightness right away, such as a stairwell, choose an LED bulb. LEDs are also the best choice for outdoor use. Many CFLs won't work in low temperatures, and those that do work will take longer to warm up in cold weather.
Are you using a dimmer? Most CFL bulbs can't be used with dimmer switches. Many LED bulbs are dimmable, but some of them will work only with specific dimmers. Also, some LEDs have a tendency to flicker or give off a buzzing noise when dimmed..
What shade of light do you prefer? Most reviewers prefer the warmer light of a traditional incandescent bulb, a shade usually referred to as "soft white" or "warm white" on lighting labels. However, others prefer a bluer light that may be identified as "daylight" or "full spectrum." The Lighting Facts labels on all new light bulbs note the bulb's "color temperature," but the term is slightly confusing since a warm, yellowish light has a lower color temperature than a cool, bluish light. The CNET light bulb buying guide says it's less confusing if you think of the light as a flame: "It starts out yellow and orange, but when it gets really hot, it turns blue." Soft white bulbs have a color temperature of around 2,700K is closest to an incandescent, while daylight bulbs are between 5,000 and 6,000K.
How concerned are you about mercury? The small amount of mercury in a CFL bulb doesn't pose a threat to your health unless the bulb breaks. In a fixture that's out of reach, such as an overhead light, that generally won't be a problem. Table lamps and floor lamps are more likely to be knocked over, however, so you might avoid putting CFLs in these fixtures, especially if you have small children in the house. If a CFL does break, the U.S. Environmental Protection Agency offers tips on how to clean it up safely.
Incandescent light bulbs haven't disappeared completely. Although the 2007 energy bill set new efficiency standards that most incandescent bulbs can't meet, a few types were exempted from the new rules. Three-way bulbs, appliance bulbs, bug lamps and colored light bulbs are a few of the specialty incandescent bulbs that remain legal -- for now. The energy bill requires manufacturers to keep an eye on demand, and if there's a sudden spike in sales for any type of bulb, the U.S. Department of Energy (DOE) will step in and set new efficiency standards for it.
In February 2016, the DOE proposed even stricter standards for light bulb efficiency. If the rule takes effect in 2020 as planned, only LEDs will be able to meet the new standards, and both CFLs and halogen incandescent bulbs are likely to completely fade from the market. The DOE says it will issue its final version of the new standards by January 1, 2017.