In my opinion, in such a large tank u need some extra UVB lighting, my tank is 24" tall and with the fixtures in place brings them down to about 21" the amount of uvb the bearded dragon receives is no where near the amount that they truly get in there natural environment. And if u need more light what would a regular fluorescent light bulb purpose serve. Except keeping cost down. It Serve's no, benefit for the reptile. The fixtures I use have independent switches which I can turn one off if need to. Here are the fixtures I use without the lens of course.
http://www.bigappleherp.com/Fluorescent-Mounting-Fixtures?sc=2&category=22 What really matters is the distance the reptile is from the lights so i added the wood log in the bottom of the enclosure to get him closer to the UVB lighting. Which, he uses all the time when not basking under the heat lamp. I have had no problems with my dragons eyes nor have I seen any ill effect with my dragon. The extra heat from the fluorescent bulb helps keep the humidity down in such a LARG enclosure. The basking spot temps are around 104 degrees right under the spot light and range from 95 to 98 degrees on different spots of the basking rock. The middle of the enclosure temps range from 89 to 82 degrees heading towards the cooler end. And the cool side range is 80 to 77 degrees . the humidity in the tank ranges any where from 20% to 35% in different parts of the enclosure. The higher humidity on the cooler side with the water dish.
hear are some pics with the lights on
The 2 tanks on the bottom are for my corn snakes and have no UVB. Need another reptile for the small empty tank.Undecided yet.
In the larger middle tank I keep my blue tongue skink that tank measures 48"L x 24"w x 18"H I only have one fixture mounted in that. And with the fixture mounted the light is about 15" from bottom of enclosure.