Almost every news story about global warming recommends that consumers switch from incandescent light bulbs to more efficient compact fluorescent light bulbs, or CFLs.
But are CFLs really that good for the environment?
Incandescent light bulbs use electricity to heat a filament to a white-hot state, producing light. Yet 90 percent of the energy used is wasted as heat, according to General Electric's Web site.
Compact fluorescent light bulbs use electricity to excite gas within a glass tube. The gas fluoresces, producing ultraviolet light which the human eye cannot see. This UV light then reacts with mercury and a phosphorescent chemical compound inside the tube to create visible light.
Because CFL bulbs do not use heat as the lighting mechanism, less energy is spent to create an equivalent amount of light.
The packaging of an N:Vision-brand CFL bulb purchased at Home Depot, for example, states that it uses only 14 watts to produce the same amount of light, as measured in lumens, as a 60-watt incandescent bulb.
This decreased demand for electricity reduces the need for electrical generation, which environmentalists point out reduces emissions from coal-fired plants.
In February, Australia announced a nationwide ban on incandescent bulbs, which will go into effect in 2010. The country's environment minister said the move will cut greenhouse-gas emissions by 800,000 tons by 2012, according to Reuters.
But this assumes that Australians will significantly reduce their current levels of electrical consumption.
What if a consumer who has a $100 monthly electric bill reduces it to $50 by installing CFLs, but then leaves the new lights on longer, because he's already accustomed to paying $100 per month?
The consumer would be using less raw electricity than before, but not that much less.
"Sometimes when you cut the cost of things, people use more of them," said James S. Shortle, professor of environmental economics at Penn State University.
"People have a certain lighting requirement," said Shortle, and they would be happy to fulfill that need more cheaply.
He suggested that people probably would not turn on their lights more often. "What they might not do is turn them off."
Manufacturers, meanwhile, tout the savings to consumers in reduced electrical costs over the lifetime of the CFL bulb.
The 14-watt N:Vision states on the packaging that it will save the buyer $46 over its lifetime. How did the manufacturer arrive at that number?
CFL makers claim the bulbs have lifetimes of 10,000 hours each, whereas most equivalent 60-watt incandescent bulbs last 1,000 hours.
Based on a rate of $0.10 per kilowatt-hour, a CFL costs $14 to power over its lifetime. The consumer would go through 10 incandescent bulbs in that time, costing a total of $60. Hence, a difference of $46 in electric costs per light fixture.
Since CFLs last longer than incandescents, consumers have to buy fewer bulbs for their fixtures, but here the cost savings are trivial.
At $3.97 for a four-pack of N:Visions versus $1.04 for four Philips incandescents, and assuming 10 incandescents used for every CFL used, a consumer opting for the N:Vision would save about $1.60 per fixture in addition to the electricity conserved.
You won't save a lot of scratch on the bulbs themselves, but at least you'll spend less time changing them.
But what about any drawbacks to CFLs?
CFLs don't operate well in frigid conditions, limiting their use for exterior lighting in cold areas.
According to a spokeswoman from Philips Lighting, most CFLs require a minimum starting temperature of minus 20 degrees Fahrenheit; below that, it's difficult for the bulb's reaction process to begin.
Other problems in cold temps include reduced light output and a pinkish glow, rather than the desirable "soft white" (actually faintly yellow) color.
Those problems alone may make nationwide bans on incandescent bulbs impractical in parts of the United States. Winter temperatures in Australia's southernmost state of Tasmania average 52 degrees Fahrenheit, but Minnesota spends most of its winters between 6 and 16 degrees F.
The bigger problem with CFLs is their mercury content.
Along with the phosphor, which can be one or many of several chemical compounds, mercury helps shift the invisible UV light into the visible part of the spectrum.
The National Electrical Manufacturers Association, or NEMA, which sets voluntary industry standards, suggests that CFLs of 25 watts or less — the equivalent of a 100-watt incandescent bulb — contain no more than 5 milligrams of mercury, the size of the tip of a ballpoint pen.
Both CFL manufacturers and the Environmental Protection Agency recommend recycling CFL bulbs, since breaking or incinerating them releases mercury into the air. The poisonous metal can then find its way into soil, water, fish and fish-eating humans.
Should you break out the hazmat suit if you break a CFL at home? The EPA offers a checklist at epa.gov/mercury that suggests you leave the room for 15 minutes, then return to sweep up and double-bag the mess — and not to vacuum unless absolutely necessary.
So handle with care, lest you end up like Brandy Bridges of Prospect, Maine, who broke a CFL bulb in her daughter's room in March and was told that professional environmental cleaning would cost about $2,000.
According to the Maine Department of Environmental Protection, Bridges was concerned about any amount of mercury in her house, even at levels far below the state hazard threshold. (Hazardous levels were found on an area of carpet "the size of a dinner plate.")
It was in response to her "nervousness" that the DEP responder who came to her house recommended the cleanup service.
Two months after the incident, state DEP officials came back and found no mercury hazard. Even so, they removed the piece of carpet — which Bridges had planned to take up even before the bulb was broken — at her request.
In the meantime, manufacturers are racing for bragging rights to the CFL with the lowest mercury content. Philips says that it sells 19 CFL products at Wal-Mart that contain 40 percent to 60 percent less mercury than the suggested NEMA level of 5 milligrams.
Whether decreases in power-plant emissions are offset by people releasing mercury into the environment by disposing of their CFLs improperly remains to be seen.
One thing's for sure: Using compact fluorescent light bulbs makes sense for anyone paying an electric bill — and who doesn't have butterfingers.