AskPablo: Mercury in Compact Flourescent Bulbs

cfl_curled.jpgWell, another week is here, another weekend is gone, and it’s time for another installment of AskPablo. I hope that some of you got a chance to see the West Coast Green Conference/Expo. Let me know if you had any suitable AskPablo questions come up. This week we will be looking at another comparison between two alternatives: incandescent and compact fluorescent light bulbs (CFLs). Last year someone raised the point that CFLs contain mercury and asked me to justify his purchase of them. Do you really want the answer? Enter if you dare.


Well, it’s true. According to the United States Environmental Protection Agency CFLs contain around 4mg of mercury. By comparison, older household thermostats contain about 3000mg (trade them in for programmable thermostats now!), and thermometers contain around 500mg (digital replacements available, make sure you properly recycle your old ones). So, 4mg is not much in comparison to other mercury-containing household items but mercury is bad stuff, in any concentration. So how much mercury does an incandescent bulb contain? Well, I’m sure there are trace amounts in the glass, metal, or solder that holds them together but I haven’t been able to find any data one this so we will assume that the amount is negligible. Debate over? Not so fast!
Both bulbs require electricity. An incandescent bulb requires about 4x more energy to illuminate the same space, so we have something to go on. It turns out that coal-fired power plants emit mercury. Surprise! Let’s see how much. Over 5 years (the life of a CFL) it may be responsible for 2.4mg of smokestack mercury emissions, so a total of 6.4mg of mercury over the life of the bulb. By comparison the incandescent bulb is responsible for almost 10mg of mercury emissions over 5 years. But CFLs can be recycled to recapture the mercury. Smokestack emissions can not be recaptured after they enter the atmosphere. So, if we want to, we could probably deduct the mercury contained within the CFL bulbs from the equation. Therefore incandescent bulbs are responsible for around 4x more mercury emissions than CFLs.
In case you don’t hate incandescent bulbs enough I have a quite overview of their wastefulness… Power plants convert fuel energy into electricity at about 30% efficiency, so one hundred units of fuel make only 30 units of electricity. Deduct for this the line losses that occur from transmission lines and other losses in converting high voltage to low voltage and we end up at around 20 units of electricity. A large part of the energy used by incandescent bulbs goes into making heat (just like my damn laptop computer), leaving around 1-2 units of energy of actual light energy. You would think that we could do better than 1-2% efficiency, wouldn’t you? Well, we can. Install CFLs everywhere, support distributed generation through renewable energy sources and natural gas cogeneration microturbines, install occupancy sensors, turn lights off when you don’t need them, replace your halogen upright lamps with fluorescent uprights, etc.
See you next week!