How CFL Bulbs Work

CFL Bulbs and Mercury

If there is an ugly truth about CFL bulbs, it's the mercury they hold within their glass covers. Mercury is a persistent and highly toxic chemical. Most humans are exposed to the poison by eating fish contaminated with methyl mercury. However, it's also possible to inhale elemental mercury vapor, like the kind used in compact fluorescent light bulbs. To see which is a bigger deal -- fish or fluorescent -- check out this related HowStuffWorks article.

So why is it there, and why don't CFL manufacturers use something else? As we mentioned earlier, mercury vapor is required to convert electrical energy to radiant energy. When stimulated by electric current, mercury vapor inside a CFL produces ultraviolet light, which is re-radiated as visible light when it strikes the fluorescent compound, known as phosphor, painted on the inside of the bulb. No other element has proved as efficient in this process, so even though the amounts of mercury used in bulbs has decreased over time, a small amount of mercury is still required for CFLs to function properly.

It's important to keep this in perspective. One CFL bulb typically requires approximately 0.000176 ounces (5 milligrams) of mercury. Older home thermometers contain 100 times that amount (0.0176 ounces or 500 milligrams), and many manual thermostats contain 600 times that amount (0.106 ounces or 3,000 milligrams) [source: GE Consumer & Industrial Lighting]. So, a single CFL bulb has very little mercury. And none of the chemical is released as long as the bulb remains intact.

A broken CFL bulb, however, can expose a person to mercury vapor. A tiny amount of solid mercury powder can also be released. For these reasons, extra caution should be taken when cleaning up a broken CFL. The U.S. Environmental Protection Agency (EPA) recommends following four easy steps:

  1. First, turn off your central heating or cooling system so fumes aren't moved from one room to another. Then open up the windows and let the room ventilate for 15 minutes.
  2. Next, it's time to clean up the broken bulb. Put on gloves to make sure you don't touch any of the mercury powder. Use a piece of cardboard to scoop up large pieces of glass. Switch to sticky tape to pick up small fragments and shards. Don't use your vacuum cleaner, and make sure all broken pieces, tape and cardboard are placed in a plastic bag.
  3. Finally, wipe the area with a damp paper towel and place the used towel in the plastic bag, as well.
  4. Seal the bag and immediately throw it away.

This should take care of a broken bulb. Up next, we'll look at what to do with a CFL bulb that burns out.