For figuring the wattage, I would use the lower number. That will be the PC
wattage and you can compare that to regular PC
aquarium bulbs and wattages.
? My other question is is one spiral flourecent of 32 watts okay?
Not being a plant guru, I'm gonna say probably, but I think you will lose some light due to the design of the bulb. This can be minimized with the use of a good reflector, but the bulb is still only gonna be a 4" bulb over a 20" tank. I might use two, centered over the center point of each 1/2 of the tank.