Hey Mr. Green,
I know fluorescent lightbulbs are more efficient than incandescents. In terms of overall resource use, however, is it better to replace a functioning incandescent bulb now or wait until it burns out? --Tom (submitted by e-mail)
I salute you for wondering about what goes into industrial processes. Some people chirp about a "postindustrial" era as if their toys were birthed by an invisible techno-god--rather than a polluting, energy-burning, all-too-earthly system.
Anyway, replace incandescents now. The resources used to produce either kind of lightbulb represent a fraction (as little as one percent, according to researchers at the Technical University of Denmark) of the bulb's overall toll on the environment. Powering the bulb in your home uses far more energy.
Say you have a 100-watt incandescent that has provided 500 hours of light. If it burns for another 500 hours, it will consume 50 kilowatt-hours. That's four times the energy a compact fluorescent bulb would require to produce the same amount of light and nearly 30 times the energy needed to produce a new CFL. Generating those extra kilowatts-hours for the incandescent with fossil fuel would require the equivalent of almost three gallons of gasoline or 35 pounds of coal.
But don't rest content just because you've installed fluorescents. Turn out the lights when not needed--having a more efficient device doesn't mean you should waste energy. And recycle CFLs, because they contain a small amount of mercury, a toxic metal.