I have to disagree with at least one of rdude's findings. I conjecture that running fluorescent bulbs is a good idea. I don't think what rdude says about startup energy is true.

Consider this: I replace a 100 watt incandescent bulb with a 20 watt compact fluorecent bulb. I turn on the compact fluorescent bulb and, according to rdude, it instantly consumes the ammount of energy equal to it being in steady state (20 Watts) for 8 hours of operation. That's 72000 Joules of energy. Assuming a fluorenscent bulb has a mass of 1/2 kilogram (it's less), and is made of solid iron(449 J/kg*K), the primary contributor of it's mass, the bulb would get to be 320 degrees Kelvin hotter than it was before it was turned on. This doesn't happen. If you turn on a fluorescent bulb, you can feel it gradually warming up, but it doesn't have a huge startup energy.

On the other hand, consider a 100 Watt incandescent bulb. The incandescent bulb radiates at least 80% of its energy as heat (a 20 Watt flourescent is said to be equivalent). So, 80 Watts of energy are wasted. Of course, if you have air conditioning, the energy is dissipated by your air conditioner. This of course opperates at well below 100% efficiency (I would venture around 35%). So, the energy used by a fluoresecent is signifigantly less.

Of course, fluorescent lights do get excessive wear from short durations of use. In most places, lights are not the primary expenditure of energy in a home.

**This node is in response to energy crisis**