subject: For Gardeners: the truth about mercury in CFLs and gardens [print this page] Compact fluorescent light bulbs are replacing incandescent light bulbs in gardens. The only concern I've really seen or heard is the mercury issue. I was at first concerned as well, until I researched a bit more and found out just how much mercury compact fluorescent light bulbs really contain.
The amount is 4 to 5 milligrams per bulb. That amount of mercury is about the size of the period at the end of this sentence; in other words, not much. I'm sure most people are familiar with old home thermometers, the ones that used rising mercury to indicate temperature. Old mercury thermometers like that contained around 500 milligrams, over a hundred times more than any compact fluorescent light bulb. Where was the hubbub back then? You'd have to break over a hundred compact fluorescents and dump them all in the same tiny pile to even get close to being even with an old mercury thermometer break.
We know how much mercury a compact fluorescent light bulb contains, but what about mercury emissions produced from powering light bulbs? In the US, about half the population receives power from coal-burning power plants. Mercury is released into the air when coal is burned, so it matters how much energy is required to power the bulb. Keeping a home garden running smoothly and growing well requires more light bulbs than just lighting a room, so it's important to consider the impact of the energy use.
The amount released is cumulative; the more power produced, the more mercury goes out. Incandescent light bulbs then, requiring far more energy than compact fluorescent light bulbs, cause comparatively large amounts of mercury emissions to be produced. Consider that a compact fluorescent light bulb lasts 7500 hours (this is a conservative estimate; in fair conditions, they can last over 10,000 hours). Mercury emissions to power a 20 watt CFL for 7500 hours would be around 3.51mg. Now, replace the 20 watt CFL with a 75 watt incandescent and power it and its replacements for 7500 hours. This would create 13.16 mg of mercury emissions. Even if the compact fluorescent broke at any point and the mercury got out, there would still be more mercury released into the environment from incandescent light bulbs.
When it's put into perspective like that, the mercury in compact fluorescent light bulbs seems far less dire, and the case for using CFLs in gardening grows even stronger. Any place powered by coal will produce less mercury if CFLs are used instead of incandescent light bulbs; that's over half the US. Couple that with all the other reasons to use compact fluorescents in gardening and you've got a clear choice: compact fluorescent light bulbs for your garden.
For Gardeners: the truth about mercury in CFLs and gardens
