How CFL Bulbs Work

The benefits of CFLs have been grabbing headlines for the last two to three years. Indeed, if you were to focus only on the buzz surrounding CFLs, you might think that changing out your incandescent bulbs in favor of their spiral cousins would be a complete no-brainer. As we'll see later, CFLs do present some challenges and concerns. But their benefits are far more numerous.

First, CFLs use significantly less energy -- 75 percent less energy than incandescent light bulbs. That means CFLs require less wattage to produce an equivalent amount of light. For example, you could use a 20-watt CFL and enjoy the same amount of light as a 75-watt incandescent. If every home in America made one such swap, enough energy would be saved in one year to light more than 3 million homes [source: ENERGY STAR].

Of course, if you're using less energy, your energy costs are going to go down. Replacing a standard 60-watt bulb with a 13-watt CFL can save a single household $30 in energy costs over the life of the bulb [source: General Electric]. Even with the higher price tag of CFLs -- you'll pay $2 to $4 for a CFL versus 30 to 40 cents for a typical incandescent bulb -- they still save you money. That's because CFLs last a long time. In some tests, they burned brightly for 10,000 hours, whereas standard bulbs burned for just 800 to 1,500 hours [source: Johnson].

The environment comes out ahead, too. A good deal of electricity coming from coal-fired power plants gets directed to the lamps and light fixtures inside your house. If you're saving energy by using CFLs, then you're pulling less electricity from the power grid. This reduces the amount of coal that must be burned, which reduces emissions of greenhouse gases. In a single year, the use of CFLs over incandescent bulbs removes as much greenhouse gas pollution as taking 2 million cars off the road [source: ENERGY STAR].

These would be dubious benefits if CFLs didn't perform well or couldn't be used in many applications, but they are, in fact, quite versatile. Several manufacturers make compact fluorescent light bulbs that can be used with dimmer switches and in three-way lamps. And many CFL bulbs can be used outdoors as long as the fixture is enclosed. Most importantly, they give off good light. In a 2007 study conducted by Popular Mechanics, CFLs burned almost as bright and produced a better quality light than a 75-watt incandescent bulb [source: Masamitsu].

CFLs are not worry-free, however. Up next, we'll look at the biggest worry -- an element toxic to living things.

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:

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

So what do you do with a burned-out CFL bulb if it contains mercury? First, you should realize that compact fluorescent bulbs are considered hazardous household items, a category that also includes paint, batteries and thermostats. You must dispose of such items properly, which means you can't simply throw them away in household garbage.

To find out your options, start by calling your local waste management authority. You can also call 1-800-CLEANUP, a service provided by Earth911 that allows anyone with telephone access to search the organization's database of 100,000 recycling and hazardous waste collection locations for more than 170 different materials. You can search the same database online at www.earth911.org.

More and more retailers are stepping up to help with CFL bulb recycling. IKEA was the first retailer to provide free disposal and recycling of used CFLs. The Home Depot joined IKEA in 2008 by launching a national in-store consumer CFL bulb-recycling program in all of its nearly 2,000 locations. Some Ace and True Value stores are offering similar programs.

As recycling becomes easier, the CFL revolution will only gain momentum. Many think that the spiral-shaped bulbs will be a brief evolutionary step toward the even more efficient light-emitting diode (LED) bulbs. A 1.3-watt LED bulb uses less electricity than a 9-watt CFL and can last for up to 11 years [source: Peterson]. Better yet, it doesn't contain an atom of mercury.

But even LED bulbs have their tradeoffs. They're not very bright, and they're exorbitantly expensive. Until manufacturers overcome those two issues, CFL bulbs will likely have the spotlight all to themselves.