What are Low-Mercury CFL Bulbs?

by Lauren Heist, Staff, Residential Lighting


From Residential Lighting E-Magazine. Click here to view this article in its entirety.

CFL Bulb Diagram Compact fluorescent bulbs (CFLs) have been touted as the environmentally-friendly alternative to incandescent bulbs because they use much less energy to operate than an incandescent bulb. But some consumers have been wary of using compact fluorescent bulbs because they contain mercury gas, which can be harmful to the environment.


Many lighting manufacturers are now making CFL bulbss that are labeled "low-mercury," but what exactly does it mean to be low-mercury? And how bad are CFLs — low-mercury or not — for the environment?


To find out, we asked Jeff McCullough, senior research engineer at the Department of Energy’s Pacific Northwest National Laboratory, to explain.


McCullough: The first thing to understand is all fluorescent lighting needs mercury, so we can’t do away with it. It needs a very small amount to work… That said, [manufacturers] are doing a lot of things to get the mercury levels down as low as possible.


[To create a CFL], we add mercury inside a tube… And on each end of the lamp there are cathodes that have what we call emissive material. And so when we put a voltage across those cathodes, they heat up, but they also emit an electron. The mercury is actually in a vapor state, so imagine all these mercury vapor ions floating around and when the emissive material is ignited or a charge is put across it, it emits an electron and in order for that electron to make it to the opposing electron on the other end of the lamp, it needs to have a conductive path. We call it a thermal electronic arc… Basically, the mercury acts as a conductor between the two cathodes. What happens is the mercury becomes excited and it emits UV light, and the human eye, depending on how close it is, can’t see it or if [you can] it’s a very light purple. And so we add phosphors on the inside of the [tube] that the UV light excites. So we shift from a very short wavelength… to the longer wavelengths to make it look more yellow or more orange or more white. The mercury is necessary for that thermal-ionic arc to take place.


Now, what’s interesting is that to maintain that arc, only takes 50 micrograms, and that is a very, very small amount… So the question that begs to be asked is why do they put so much mercury in there when it takes very little to maintain the arc? The problem is that over time the mercury becomes unusable for the process and it becomes [attached] to the glass… it kind of gets absorbed by its surroundings. So that’s why we need to have enough mercury so that there’s enough mercury at the end of the lamp’s life to still operate… Over the last five years or so there’ve been a lot of technical advances that have been made by the manufacturers to do what’s called a barrier coating. Basically it’s a coating that goes inside the lamp that minimizes the amount of mercury that gets lost… so that’s one way that we’re able to use less mercury is to make sure that the amount that’s there remains available throughout the lamp life.


I was at a recycling facility about two weeks ago, and it was a facility where they took fluorescent lamps and they crushed them up and they separated the phosphors and the glass and they deposited them in a 55-gallon drum. And what I found intensely interesting is that 55-gallon drum held 36,000 lamps — we’re talking the linear, 4-foot stuff. Out of all that material, they are able to reclaim one pound, or about a thumb’s-worth of mercury… It’s important to know that we’re not talking a huge amount of mercury here…


There have been studies done that even though mercury may make it into the environment from a CFL that’s in a landfill and maybe it breaks and some of the mercury gets way down into the ground water or something, because it saves so much energy, you actually burn less coal, which is the primary source of energy in the United States. And coal, in and of itself, puts a lot of mercury into the environment. If you burn coal, one of the bi-products is mercury. So there’ve been studies that have been done that say by using a CFL, because you’re using less energy, you’re burning less coal and there’s less net mercury in the environment…


[The push for low-mercury CFLs began] about three to five years ago by the European Union. And they established maximum mercury levels for compact fluorescent lamps and linear fluorescent lamps. And the thresholds that were established were 5 milligrams [for CFLs] and 10 milligrams for four-foot linear fluorescents… Also China has embraced those same thresholds and the U.S. is doing it as well.


And what you’re seeing is major lighting manufacturers — the Phillips, the Osrams, those folks — they make the lamps all over the world to be marketed all over the world, so it doesn’t make sense to them to make one lamp that’s 7 or 8 grams of mercury and another that’s 5 just so they can market it different countries or areas of the world. So they make one lamp. So because of the European Union and China and the new requirements from the Energy Star program, these lamp manufacturers are voluntarily reducing the amounts of mercury, and some of them have been doing it for a while….


The truth is everybody is doing it now. Some are just better than others at marketing it. There are still higher mercury level lamps out there made by what I would call second- or third-tier manufacturers. You’re still allowed to make them in certain parts of the world. And they’re probably 5 milligrams at the most… [The average low-mercury CFL] is in the 2 to 2.5 milligram range.

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