Dimmable fluorescent lights were used beginning ca. 1970 in some places, most notably in a couple of airplanes for area lighting in the passenger compartment. These required a completely different kind of tube, however, and an external high frequency and high voltage power supply for each bulb. The high frequency was to make it easier to get the high voltage, and the essentially RF frequency could be modulated (PWM?) to change the current through the tubes/bulbs.

I haven't seen specs on how they're being built, but the guess is that the "modern" low energy bulbs use the same principles. The base contains a small frequency/voltage converter that's actually applying a couple of hundred(?) volts inside the tube, probably at some higher frequency like perhaps 400 Hz(?). The absence of a separate "starter" - required with old-fashioned long tube fluorescents - implies at least that something inside the bulb is working in much different manner.

When we moved into our current home, we found that the previous owners had "decorated with lighting" so that we needed 11 different kinds of bulbs to keep all the installed fixtures working. In two cases I've actually replaced fixtures to get rid of the more exotic kinds, and in most of the rest of the place I've just "uglified" things by using less fancy bulbs. With the exception of a set of yard lights, a couple of halogen floor lamps, and about four desk lamps (that will eventually get converted) I've been using the plug-in low power lamps everywhere that incandescent bulbs were installed for at least the last 4 or 5 years.

I could brag that replacing all the light bulbs saved us tremendous amounts on our electric bills, but I'd have to figure out how much of that was due to the hot tub breakdown. I had already calculated that the tub was costing us "more than $150/month" if we turned it on, so I wasn't too sorry when it became "unfixable."

We have found that the new bulbs do not give the impression of lighting things as well as the "equivalent" incandescent bulb, but since a "100W-equivalent" bulb only uses 47W actual, I've considered it safe to replace in 60W rated fixtures with "100W-equivalent" bulbs and with that conversion the apparent lighting is much the same, perhaps a little "softer," still with some reduction in power usage.

The new-style bulbs do last somewhat longer than incandescents, but the claims on the package are somewhat optimistic. I'm not sure that the savings on energy consumed and on bulb replacements would be much better than "break-even" if the new bulbs are bought singly at common retail outlets, but there is a definite $aving$ if bought in small bulk quantities at the bulk outlets (Sams/Costco) or in bulk packages at the lumber yard (Home Depot/Lowes).

Some of the replacement bulbs carry a warning that they should be used only in "base down" applications, although this warning doesn't appear on most newer kinds. There does seem to be a slight reduction in bulb life, at least for some, if used in "odd angle locations." This might be something to watch for on the packaging if buying a large bunch of them for general replacement.

John