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In the May 2007 issue of Popular Mechanics, we tested seven popular compact fluorescent light bulbs (CFLs) and found that the light quality in all of them topped that emitted by traditional incandescent bulbs. Following that lab test, we received a lot of questions from readers regarding the environmental impact of the mercury contained in CFLs. For more of the lowdown on these energy-saving bulbs, we crunched the numbers and checked in with the Department of Energy and Russ Leslie at Rensselaer Polytechnic Institute. —Julianne Pepitone and Emily Masamitsu

Why do CFLs require mercury to produce light?
Compact fluorescent bulbs are made of glass tubes filled with gas and a small amount of mercury. CFLs produce light when the mercury molecules are excited by electricity running between two electrodes in the base of the bulb. The mercury emits ultraviolet light, which in turn excites the tube’s phosphor coating, leading it to emit visible light.

How much mercury is contained in a CFL?
Each bulb contains an average of 5 milligrams of mercury, “which is just enough to cover a ballpoint pen tip,” says Leslie, associate director of the Lighting Research Center at Rensselaer. “Though it’s nothing to laugh at, unless you wipe up mercury [without gloves] and then lick your hand, you’re probably going to be okay.”

How do CFLs and incandescents compare in terms of electricity consumption?
On average, CFLs require about 25 percent of the electricity as their incandescent counterparts to produce equivalent light. Replacing an incandescent with a CFL ultimately decreases the amount of electricity the nation’s power plants must generate and, in turn, the amount of carbon dioxide—a powerful greenhouse gas—that they emit into the atmosphere.

How much mercury do power plants emit to light a CFL?
About 50 percent of the electricity produced in the U.S. is generated by coal-fired power plants. When coal burns to produce electricity, mercury naturally contained in the coal releases into the air. In 2006, coal-fired power plants produced 1,971 billion kilowatt hours (kwh) of electricity, emitting 50.7 million tons of mercury into the air—the equivalent amount of mercury contained in more than 9 billion CFLs (the bulbs emit zero mercury when in use or being handled).

Approximately 0.0234 mg of mercury—plus carbon dioxide, sulfur dioxide and nitrogen oxide—releases into the air per 1 kwh of electricity that a coal-fired power plant generates. Over the 7500-hour average range of one CFL, then, a plant will emit 13.16 mg of mercury to sustain a 75-watt incandescent bulb but only 3.51 mg of mercury to sustain a 20-watt CFL (the lightning equivalent of a 75-watt traditional bulb). Even if the mercury contained in a CFL was directly released into the atmosphere, an incandescent would still contribute 4.65 more milligrams of mercury into the environment over its lifetime.

Why are incandescents less efficient than CFLs?
Unlike compact fluorescents, incandescent bulbs produce light by heating the metal filament inside the bulb. When electricity passes through the filament, its temperature rises to 2,300 degrees Celsius, with the heat causing the filament to glow white-hot and emit light. But only 5 to 10 percent of that electricity is transformed into visible light. “In an incandescent bulb, much of the electricity is used for heat, which is not efficient,” Leslie says. “Fluorescent lights use electricity to do much more than heat a solid object.”

How much of a difference can CFLs really make?
According to EnergyStar—a program run by the Environmental Protection Agency—if each U.S. home replaced just one of its incandescent bulbs with a CFL, the electricity saved each year could light 3 million homes and prevent greenhouse gas emissions equal to that of 800,000 cars. And with a recent study for the U.S. government saying that a single 24-watt CFL’s lifetime energy savings add up to the gas equivalent of a coast-to-coast Prius road trip, it’s probably time to get moving on your energy footprint.

What is the proper way to handle a broken CFL?
Open the windows and let the room air out for 15 to 30 minutes, then remove as much material as possible without a vacuum cleaner. Using disposable gloves, scoop the glass onto a piece of cardboard and wipe the area with a wet paper towel. For smaller pieces of glass and powder, use duct tape to pull up the fragments and wash your hands after cleaning up the debris.

What is the proper method to dispose a CFL?
Check if your local recycling center has services available for CFL disposal by calling directly or by visiting Earth 911. Plus, as retail giants such as Home Depot and Wal-Mart amp up their CFL offerings, IKEA recycled 156,301 pounds of CFLs in its 2005 fiscal year with its “Free Take Back” recycling program that puts a collection bin in each store. If that wasn’t enough incentive, officials are looking into providing more consumer bonuses for CFL recycling, Leslie says, and they may even add a deposit value much like cans and bottles. Leslie promises: “Over six months to a year, you will see changes.”
Reader Comments
18. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
Re: #3: "how much mercury would be thrown into our society when 1 billion CFls are disposed?" The article says each cfl has 5 mg of mercury. so if you mean how much will be thrown away when people dispose of them and don't recycle, 5mg x 1 billion = 5,000 kg

17. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
I had a CFL bulb all of a sudden started smoking white smoke . the smell was awful. It later was leaking liquid that also smelt awful ..I'm still not sure what it was all about ..till I know further i'll stay with the old bulbs .

16. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
What about the energy used in the production of the two type of lights?

15. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
You did not cover the impact of all those cfl,s winding up in a landfill somewhere. whats the impact to the enviroment

14. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
The CFBs are all made in China so if we ramp up use alot the Chinese will build more coalfired plants to produce them. Whoopee!

13. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
Why can't we use LEDs for home lighting? Aren't they far more efficient and long lasting than even CFLs?

12. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
What? Not one word about the cradle to cradle of the ballast bases?

11. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
It seems from the above that CFLs might actually cause a slight increase in mercury emissions nationwide. (I'm actually not particularly worried, since about 99% of worldwide mercury emissions come from sources other than U.S. coal plants, but that is another story, and one I won't say more about here.) The example with the coal plant shows that when coal the fuel for electricity, that there is a slight decrease in mercury emitted when a CFL replaces an incandescent (5 mg increase from the CFL when it eventually is discarded, if there is no recycling, minus the mercury savings at the coal plant from the 75% reduction in electricity needed, which is about 9.65 mg, for a net savings of about 4.65 mg). But the 50% of electricity generated in the U.S. from sources other than coal emits no mercury. So for this electricity, using the CFL would cause a 5 mg net increase, slightly larger than the 4.65 net decrease if coal is the fuel. Not a big deal, obviously, and over time more mercury will be recyled - just as, over time, at least 75% of the mercury from U.S. coal plants will no longer be emitted, by law.

10. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
Dear Sirs You are off on the amount of mercury in 9 billion bulbs, I figure that about 6 tons of mercury per 1 billion cfl bulbs, so 50.7 million tons of mercury would be equal to about 4,450,000 x 1 billion cfl bulbs not 5 billion. this gives a much larger # of cfl bulbs. Which makes them look better. Thank you.

9. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
Since the EPA states that we could save so much energy if every house replaced just 1 bulb with a CFL, then why doesn't the EPA or US government do something about the sale of incandecants? (i.e. limit the production/sale of incandecants)

8. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
Wow, thanks for this vital information ... now I realize how dangerous the mercury contained in CFL bulbs really is: 1) If my child breaks one of these bulbs and then gets the residue on his hand, he could die 2) I have to use special handling techniques to dispose of them (or visit my recycling center 20 miles away), rather than just tossing the old incandescent into the trash can. 3) If the babysitter breaks one of these bulbs, but isn't aware of the special handling required to clean up the toxic substances (such as opening windows, not using a vacuum cleaner, using duct tape to pick up pieces... then my kid could get poisoned.) That's not really something I want to leave to the 16-year-old sitter. Quite eye-opening. Why would any parent put these toxic bulbs into their home environment where their children are?

7. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
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Would like to see numbers associated with the cost in air conditioning to compensate for the heat generated by incandescent bulbs. Must be considerable considering the inefficently of the bulbs. Thanks

6. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
you only mention CFLs what about all of the other flourescent tubes I see everywhere they have mercury too. what happens with them I dont want a new law forcing me to switch . I would switch any way Proding an incentive to switch other than a law is the way to go

5. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
Your article has a gross mistake: The US emissions of mercury are on the order of magnitude of 57 tonnes/year, not 57 million tonnes. Thank goodness there is not 1/5 of a tonne of Hg/person/year emitted by US power plants. See: http://www.epa.gov/oar/mercuryrule/basic.htm

4. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
The figures cited don't add up. 1971 billion kWh with .0234 mg Mercury released per kWh comes to some 46121 kg of mercury or some 46 metric tonnes of mercury released not 50.7 million tons of mercury. This 46 metric tonnes tracks well with the statements 9 billion CFLs containing 5 mg of mercury or 45 metric tonnes.

3. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
I've asked this question of Instapundit...have not seen it anywhere else and got no answer: how much mercury would be thrown into our society when 1 billion CFls are disposed? What future harm is there?

2. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
Very helpful information, thanks!

1. RE: Compact Fluorescent Bulbs and Mercury: Reality Check
Regarding the reported energy savings of CFLs over incandescent, does this take into account the winter months for us northerners where the wasted energy from lighting the bulb would simply help heat the house?