Those fluorescent tube light bulbs that are common in many offices and industrial rooms of the house are energy efficient, but they contain a small amount of mercury, which can be dangerous, especially if one of the tubes breaks when you replace it. If a tube light shatters, have everyone (including pets) leave the room. Turn off the central heat (or air conditioning, depending on the time of year) so it does not recirculate the mercury-laden air. Use damp paper towels and large pieces of tape to pick up all the pieces, and place everything in an airtight container. Then tape the lid securely on the container and dispose of it in the trash. Then consider safer lighting alternatives, like LED bulbs, that are mercury-free.