No it's not the wattage, it's the wave length. You could expose with
regular daylight fluorescents if you're only doing carbon tissue. And
perhaps platinum. But for cyanotype & probably for gum, you need a
higher UV output -- which is why people use blacklight fluorescents.
We worked this to death last fall. Anyone remember the month?
Incidentally, there's no reason not to use the same lightbox & change the
bulbs if that's convenient. I worked that way for a long time -- had a
knock down set up on a table top was fine for up to 8x10.
Judy