from wiki:
"The bulb is normally 25 to 40 watts. It may take 45 to 60 minutes for the wax to warm up enough to freely form rising blobs (depending on the original temperature). It may take 2 to 3 hours if it has been in a cold room for a long time depending on the temperature." If you use a house hold incandescent bulb that draws 40 watts, perhaps 35watts are converted to the form of energy we call "heat". I don't have any exact figures at hand but that's pretty close.
If you use a CFL bulb that draws 40 watts less than 20 watts are converted to heat, and the bulb will be relatively brighter as the remaining energy is more efficiently converted to "light".
That's why we use lower wattage CFLs to get the same amount of light that an Incandescent puts out.
So you'd need to find the wattage of CFL bulb that produces the same amount of heat to achieve similar performance. Maybe a CFL that draws 80 watts?
If the primary goal is to use the bulb as a source of heat... the incandescent is the more efficient choice.
If the primary goal is to save on power consumption then the lava is going to take longer to "flow".
:-)
best regards,
mike