No, any type of tubes will work, in fact the smaller ("compact fluorescents, as we call them in USA) usually give off more actual light per watt and so don't match that guideline as well as T8 (1 inch diameter) and T12 (1.5 inch diameter) do. Its also true that what freshwater plants need is just plain.. light, and that a good deal of the fuss over spectrum (color) is less necessary to worry about than you might think. That said, however, its true that blue ranges promote more algae (very white/blue "actinics" designed for growing algae to feed the reef creatures in salt tanks will often promote too much algae in fresh water I believe) and its also true that combining a couple of different spectrums can sometimes create a really nice look to the color of the tank (can't find that thread where Aaron or Dave Spencer or somebody showed a picture of a combo of (cool white and something else?) that gave a great tank look as opposed to straight use of one or the other spectrum -- anybody remember that thread?)
Another interesting thing about the 2 w/g guideline is that plants themselves vary quite a lot in how much light they need to stay in good shape.. at least I was surprised at how little the slower growth "easy" plants really need. Of course, what the 2 w/g line is all about is trying to roughly find that point at which the amount of light is "driving" the growth so strongly that artificially added CO2 becomes a must in the tank, but I assume you know that.
~~waterdrop~~
