How can I improve my bearded dragon's enclosure?

Actually Petmountain.com has cheaper prices on many items. I should say they have the cheapest prices on most pet items. I have bought from them on many occasions with good experiences. Most items I ordered are fish equipments, and some medications. Yes, I shop around a lot on the internet for price comparison.

Zoo Med ReptiSun HO UVB Bulbs for example, their (Petmountain's) 48" lamp is cheaper than the 15" lamp from drsfostersmith.

Thatpetplace.com is another option. Their price is about the same as drsfostersmith, and they offer 10% off + Free shipping on orders over $100.
Check the same Zoo Med ReptiSun HO UVB Bulbs on their site. After the 10% off, they are even cheaper.

I wonder what is the difference between the lights used for reptiles and the lights for fish. I use T5HO day light lamps for my aquarium plants. If plants can use it, why can't reptiles?