I was starting to wonder just how much energy a compact fluorescent bulb saves in terms of carbon footprint. It's widely known that you can use a lower wattage CFL bulb to replace a given incandescent bulb; e.g., the light given off by a 23 W CFL bulb is the same as that of a 100 W incandescent bulb.

However, CFLs also contain mercury (on the order of 5 mg per bulb). Disposal regulations vary widely; in my area of the woods, there's some confusion as to how households are supposed to dispose of them. We'll play responsible citizen here and take them to a recycling center.

In my county, there are three sites which accept CFLs. The nearest one is in Poulsbo, a 25.2 mile round trip.

Let's assume it's time to take that bulb to the recycling center. (Ok, normally I would bundle them up and take a bunch at a time.) In my 2000 Honda CR-V, this trip would consume a gallon of gas. According to a random environmental site on the Intertubes, this is 10.9 kg (24 lbs) of CO₂.

Yikes. That sounds like a lot. Does this offset the benefits of a CFL?

The average lifetime of a CFL is 15,000 hours. Assuming our earlier 23/100 W bulb comparison, that's a difference of 1155 kWh over the lifetime of the CFL. According to this carbon calculator, 1 kWhr of electricity results in 0.43 kg of carbon emissions.

That's a 496 kg; discounting our (silly) trip, I will have released 486 kg less CO₂ into the atmosphere -- that's half a ton.

Ok, I can rest easier now. :-)