I saw this thread yesterday but haven't had time to give it a decent response. I'll try now. First off, yes, you can indeed dim flourescent lighting. The downside is that dimming ballasts for a pair of lamps run at upwards of $75 (when you can even find them). For the size room you mentioned with indirect light on the perimeter I figure 4 four-foot T8 tubes along each of the longer walls and 3 along each of the shorter ones. That's 14 tubes and 7 ballasts, plus the associated control switch (dimming ballasts all use a special switch which is manufacturer specific to control the dimming). Lutron seems to be the big player in dimming ballasts right now. More of their product is geared towards 277 VAC commercial lighting rather than 120 VAC home lighting. However, they do have 120 VAC dimming ballasts. Sometimes these come up for sale on eBay. Besides the cost, another drawback to dimming ballasts is you get dimming to at best 1%, more often 10% or more. Because of the way your eye works (logarithmic response) reducing the light levels to 1% will mean an apparent brightness of 10%. Reducing to 10%, which will more likely be the case with most dimming ballasts, will mean an apparent brightness of around 30%. In other words, not a great amount of dimming. If your budget is really tight you can sometimes dim fluorescents on magnetic ballasts using a standard incandescent lamp dimmer. I did this in my bedroom for years before buying the 4-tube T8 fixture a few years ago. You won't get a great amount of dimming (maybe to 30% at best). You run the risk of prematurely destroying the tubes if you run them at too low a power level without heating the cathodes. Also, I don't recommend magnetic ballasts anyway because of the flicker (and this gets worse when you dim them with a lamp dimmer).
All is not lost, however. If you don't care about dimming, or can live with a couple of different light levels instead of continuous dimming, then fluorescent strip lighting is still a viable option. Perhaps you can use the 14 32W tubes I mentioned earlier in tandem for your "high" setting. This would give you roughly 40,000 lumens which would be about right for a 300 square foot room. Additionally, you could perhaps rig switches so you can have half the lights on each switch. This gives you the option of a 50% "medium" setting. For the "low" setting maybe have one 17 watt T8 tube centered on each wall controlled by a third switch. The respective lumens on high/medium/low would be roughly 40000/20000/5500. Apparent brightness levels to your eye would be 100%/71%/26%. Again, this isn't a spectacular amount of dimming but if you can live with it it can be implemented very cheaply. A big drawback would of course be slightly uneven light distribution when some of the tubes are off. Another drawback would be uneven wear on the tubes since all wouldn't necessarily be on at the same time. On the plus side you have high efficiency and wide choice of color temperature.
OK, that takes care of fluorescent so on to LED. LED interior lighting isn't yet mainstream so the cost will be high and the options limited. Still, if I were to do this I could use about 200 of the new Cree XR-Es. This would give about 135 lumens each when driven at 700 mA, or 27000 lumens total. This is not too far off of the fluorescent solution. Power consumption would be a bit more (about 500 watts counting driver losses instead of roughly 420). This is obviously because although the Crees are currently the most efficient power LED available (I've independently tested them at efficiencies of 75 lm/W when driven at 350 mA) they are still less efficient than the 90 or so lm/W of T8 tubes. However, note that in both cases we are talking bulb lumens. When you put fluorescent tubes in an indirect lighting setup most of the light from the side of the tube facing downwards will be lost. At best you'll probably end up with the same 27000 lumens hitting the ceiling as you would with LEDs. Since the Crees direct 100% of their lumens into a 180° cone towards the ceiling, all the light goes where you want it. In other words, you're taking less of an efficiency hit than you thought at first. A major advantage of using LEDs is of course infinitely variable dimmability down to whatever light level you desire. You can go to 0.1% or less if you wanted to without complex, costly controls. Another advantage is very long life. Even at 700 mA if the LEDs are properly heatsinked you'll be looking at 50,000 hours or more until they reach 70% of initial brightness. That's about 23 years if used 6 hours a day. Since I assume that since you want dimmability the LEDs will be operating at far less than 700 mA most of the time then they will probably outlast you. Disadvantages? Cost for one. The LEDs alone, even discounted, will probably run you $1200. After that you'll need circuit boards and heat sinks. In the end you would probably be looking at upwards of $3000 or more. A second disadvantage is that color rendering will be good, but not as good as with fluorescent. A third disadvantage will be tint variation, even among LEDs from the same tint bin. Like I said, LED isn't quite there yet. Check back in about 5 years and my guess is you would be able to do this for under $500, perhaps even less, and the LEDs would have better color properties. On an even more interesting note Cree and Seoul Semiconductor plan to ramp up efficiencies of their commercial products to 145 lm/W within 15 months so an LED solution then would use less power and fewer LEDs than the current one. Current off-the-shelf solutions mostly use cheap 5mm LEDs which will lose a lot of their brightness after a few thousand hours.
This takes us to the last solution-incandescent. $1400 is not exactly cheap. In fact, you can probably do the setup with dimming ballasts for the same or less. The only hard part is finding them. Of course, with incandescent you'll have infinite dimmability. However, the disadvantages are many. First off, those so-called long-life incandescents get their long life by underdriving the filament. This makes them even less efficient than regular incandescent which is already nothing to write home about. Second, dimming incandescents doesn't save as much power as you might think since efficiency drops further upon dimming. For example, incandescents dimmed to 10% of their maximum output are still using about 30% of their maximum power. Basically as you dim them they turn more and more into miniature heat lamps. Third, as you well know there is by definition a color temperature shift when dimming incandescent. They get more red as you dim them, and their color temperature to start with isn't exactly optimal for lighting. Can anyone say major eyestrain? LEDs and fluorescents don't have this color temperature shift when you dim them. Well, they do, but to a much smaller degree which is barely noticeable. Fourth and already touched upon in other threads, incandescents are basically available only in one color temperature-a sickly yellow one. Either you like it or you don't. My feelings on this are already pretty well known. They do have blue filtered incandescents but I don't know if any are available for the system you mentioned.
I think of all these choices I'd choose for now between the two flourescent options I mentioned. In five years time, maybe sooner, I would certainly go LED. Either way, once you finish the project please post some pictures. I'd love to do a similar setup, perhaps in the basement.
