It’s the small amount of mercury that gives CF lamps their efficient glow, but it’s smart to take precautions to avoid exposure. Most new CFs have 4 to 5 milligrams of mercury, and several brands have as low as 1 milligram. In contrast, a typical watch battery has 25 milligrams of mercury, an old hospital thermometer has 500 milligrams, and an old home thermostat has 3,000 milligrams. Especially in coal-burning regions, using incandescents actually results in more mercury released into the environment, since they use more energy, and burning coal is the biggest source of this neurotoxin.
Avoid putting unprotected CF lamps in rooms where children sleep or play, since young ones are most susceptible to harm from mercury, and are more likely to break something. If you want to be safe, cover the bulbs with full fixtures; consider halogens or LEDs; or check out “safety” CFs, which have a silicone covering that’s designed to contain the mercury.
For perspective, the Lawrence Berkeley National Laboratory concluded that you are likely to take in more mercury from one meal of fish than from being near a broken CF. Still, if a CF or other fluorescent does break, clear everyone out and vent the room for at least 15 minutes. Carefully sweep up the pieces, place them in a sealable container, and take it to a hazardous waste disposal center.