The spiral bulbs are compact fluorescents. They contain their own electronic (usually) ballasts and so you just have to connect them to the mains.

They are almost all triphosphor fluorescent tubes, and the ones you find in regular stores are almost all warm white, colour temperature near 3000K. If you look on the bulb you may find a colour temperature (eg. 2700K, 3000K, or 4100K) or you might find a colour designation (eg. 730, 840). You can find cool white and daylight bulbs if you look hard, and it is also possible to find gro-lux type purple compact fluorescents online.

Light output is comparable to a straight tube fluorescent of the same power, although lifetime is usually less than a straight tube. 46W of fluorescent light for 10 square feet of trays isn't very much. Its probably OK as a supplement to natural light, but really you should be looking at double the amount. I'm guessing you also have them quite far above the trays because they are quite small, so you are probably losing a lot of the light to other parts of the room. I'd aim for double that amount of light, although I have no real idea of what is coming through the window. Use the lights for 14-16 hours per day.

Incidentally, this type of bulb emits most of the light out of the "sides", very little through the base (duhh!), and not a lot through the "top" of the spiral. Mount them horizontally above the trays and put a reflector, or even just a white sheet, above so half the light isn't just going into the ceiling. The non-spiral "stick" compact fluorescents emit almost all of the light through the sides which can give you a little extra effectiveness for a grow light.

thanks for the thorough explanation Shrubs! I've got them about 6" above the trays, but as you suggested I will put them horizontally and lower. I was actually wondering about the best position. How about attaching some foil paper to cardboard and mounting above? Perhaps it's just best to invest a few bucks in a fixture and get the long bulbs.

Stonato~

Aluminium foil (for cooking) makes a good reflector, but a good white card is just as good. We tend to think that reflectors have to be "shiny" but a bright white surface reflects up to 90% which is about as good as a reflector. The reflection is diffuse so white surfaces are not so good for focussing light on a small area. I use my lights in an enclosed white propagator box with no reflectors, just the walls of the box.

It may be worth setting up 48" shop lights if want to light that many trays and you plan to have the trays under there for several months every year, or want to use lights throughout the year. Long-tube fluorescents are easier to get in special spectrums, usually a little more energy efficient, cheaper to replace, and last longer, than the spirals. All this of course is irrelevant if you never use the tubes long enough to need replacing or to claw back the cost of the special fittings. Also consider that it is recommended to replace the tubes after less than half their full life because the light output drops, and you might wonder what you will do with all those half-used fluorescent tubes. The compact spirals can just go in the porch light until they completely expire :)