Should you wait until your SUV falls apart before replacing it with a hybrid? Should you keep using your 1972 refrigerator because it still runs, even though replacing it with a new one will save enough energy to manufacture several?Buy a 5-pack of CF bulbs and wait until a conventional bulb dies. Replacing a functional Edison bulb for without reason is not very treehuggerish.
A compact fluorescent costs about $1 in energy to manufacture; a tungsten bulb much less. Replacing an incandescent with a cfl will save $1 in energy within three months. If you left it in for several months, causing more CO2 and resource waste than if you changed it immediately, were you very treehuggerish?
According to Kevan Shaw, an architect in the UK, sometimes it wastes energy to switch from magnetic to electronic ballasted fluorescent luminaires before the end of life of the former, because of the energy required to manufacture the entire latter luminaire. This is the case because the difference in efficacy is 20%, and the luminaire contains kilograms of materials. A compact fluorescent weighs much less, and is at least a three-fold increase in efficacy over tungsten lights.
Put the old technology out of its misery. A lame horse can still be a companion, but a light bulb?