I'm so glad you asked that question. I have a great source for compact fluorescent bulbs--it's Energy Federation, Inc. The website is energyfederation.org or efi.org. Go to 'Consumer Division' then 'Lighting' then 'Bulbs.' They have every imaginable compact fluorescent bulb with good information about warm v. cool v. daylight, efficiency, and life on each bulb they sell. I bought dimmable c.f.'s there that work great and have a nice warm color. They cost $6.50 each for 15 watts (60 watt equivalent) or $6.75 each for 20 watts (75 watt equivalent). I also bought a great floor lamp there that has a very bright circular fluorescent bulb. Oh, yes, I bought candelabra-base bulbs there for my dining room light fixture. Rose

When you say "...that operate dusk to dawn and also brighten for a minute or so when they sense motion", do you mean that the floods are dimmed all the time, and then when they sense motion they brighten to full strength? If so, then we have the same at our house -- 2 sets. First off, since they run in dimmed mode most of the time (ours dim to about 50%), the only kind of CFL that is going to last without the ballast crapping out in mere weeks is a dimmable CFL. Additionally, non-dimmable CFLs on a typical dimmer circuit/appliance will play havoc with the circuit -- humming, flickering, etc. Are you using those? If not, that's issue #1 for you. As to your specific non-working symptoms, I'm guessing they're because of an incorrect (i.e. non-dimmable) CFL being used. I can't guarantee that is your answer, because I have been unable to find a dimmable CFL flood in the proper size for outdoor applications that I can try at our place. Nobody appears to make a dimmable, outdoor PAR38 CFL -- they are all indoor only. So, we make do with 60w halogens and bite that bullet for the extra few dollars a year it costs.

Cold fluorescent lamps are dimmer, and they brighten as they warm up. Some are worse than others; the lamp design affects how quickly they warm up and how noticeable this effect is. Typically it lasts from a fraction of a minute to a couple of minutes. I have a few R-flood CFs that take several minutes, but they're an exception. Additional circuitry in the ballast (base) can compensate for this effect, but it's seldom used because of consumer resistance to price in retrofit CFs.

If you don't want to spend the big bucks for dimming, you can do what we did in our kitchen. We had two 4'fluorescent lights installed. Each of them had two ballasts controlling two tubes in each fixture and we had the electrician wire the ballasts so that there were two switches. One switch turns on the inner tubes and the second switch turns on the outer tubes of both fixtures together. We usually only need to have one switch on with 4 tubes over a 18' area, but during the winter months we will use all eight tubes at one time. I might add that we did this 20 years ago because I wanted to have some way to control the lighting to only have 40% at one time. To this day, many of my clients will do this rather than put the dollars into dimming their fluorescents. It works rather well.