You know that scaremongering that goes on about mercury and how cracking a low-wattage CFL (compact fluorescent lightbulb), is supposed to be so dangerous? Well, Popular Mechanics has done a little Fermi estimate (a back of an envelope calculation) to show that actually using CFLs (despite their mercury content) will ultimately reduce the amount of mercury in the Earth’s atmosphere:
CFLs contain about five milligrams of mercury, that’s a very small amount, about enough to cover the dot at the end of this sentence. A watch battery contains 25 milligrams and a manual home thermostat has hundreds of times as much at about 3 grams. Even breaking a CFL bulb is not likely to expose people to enough mercury to hurt them. Now, consider that burning fossil fuels is the main source of mercury in the environment.
A conventional smoke-belching powerplant will release about 10 milligrams of mercury into the atmosphere to power an incandescent light bulb but the energy needed for a CFL is a fraction of that at about 2.5 milligrams. Multiply those numbers by the numbers of lightbulbs around the globe (millions, billions?) and that’s a fourfold difference in mercury released to power incandescent versus CFL.
Of course, PM doesn’t discuss the many other factors that might have to be taken into account such as the higher production energy, materials costs of CFLs versus incandescents, and whether or not those are offset by the longer life of CFLs. It could be more interesting to compare conventional incandescent filament bulbs with their equivalent lumen value in LED bulbs…