Skip right over the pet store bulbs and go straight to Home Depot or Walmart! You'll pay significantly less and get the exact same bulb.
My favorite lights for added brightness are linear fluorescent lights in the 5000K range but 6500K is even brighter (both ok, they're in the daylight spectrum), which are usually sold in a 2 pack for just a few dollars. So I'll have a double linear fixture with the UVB bulb on one side and the daylight bulb on the other. They really add a lot of brightness, don't add a lot of heat, and plants thrive under them.
I do the same as Olimpia. I use @ 48 inch tubes one 6500+Kelvin and one UVB tube. I also have hanging heat bulb that is just a 50 watt regular light bulb. Anything in the 6500K encourages plant growth. I have this same setup over 8 cages and works great. Although running out of room at the top cause I also use auqazamp rain domes.