Another problem: The dimmer is no longer able to bring the light way down.
Traditional dimmers are often unable to operate LED bulbs: They may flicker or fail to respond—a syndrome known as "dead travel." In other words, don't assume a bulb labeled dimmable will jibe with the dimmer you've got. Go to the bulb maker's website to see which dimmers go with which bulbs—or consult the Lutron LED Control Center of Excellence, which runs a toll-free hotline for frustrated consumers: 877-DIM-LED8. Smartphones may turn out to be the ultimate solution; Philips already makes bulbs whose color and brightness are controlled by an app.
Can I stick an LED bulb in any fixture?
Pretty much. Just match up your old bulbs' bases with LED versions, taking care to also compare lumens, or brightness levels (again, a lower-lumen bulb may be more pleasing). Some new bulbs are surprisingly good at mimicking the familiar Edison, and one company, Switch, has introduced the first three-way LED bulb. To soften the beam and make it less direct, manufacturers install multiple LEDs, reflectors, lenses, and diffusers within the bulbs. Some bulbs look a little funny until you turn them on or put them behind a shade or inside a glass globe. But be aware that some LED bulbs cannot be used inside enclosed fixtures or capped recessed lights. (Read the fine print.) As Ray Johnston, a staff scientist at 3M, explains, LED bulbs have "heat sinks"—fins or another way out for the heat generated when energy passes through the semiconductors—which help them use much less wattage and emit much less heat than incandescent bulbs do. But on the flip side, LEDs are more sensitive to their surrounding temperature and need a decent amount of airflow to work well. Overheating won't make a bulb explode, but it will shorten its life. As for cold temperatures, unlike CFLs, LEDs do fine outdoors.