Yeah that's a T5 tube. They're great. Nice and powerful. Perfect for larger tanks.
They can have too much UVB but if you provide a gradient the same way you would with temperature they can move to an area of lower UVB. Based on reading and some of my own measurements, they bask between about 3-6 UVI (roughly) so that's what I try to provide over the basking area. They are exposed to much higher levels of UVB during mid day but from what I've read they tend to hide then so I shoot for mid morning and late afternoon levels when they're usually basking.
This all comes down to the type of bulb and the distance the bulb is from the basking area. You can add additional bulbs, but that just widens the area of exposure rather than intensifying the output which is appropriate in some cases. I like to have the UVB cover the basking area which is just a bit bigger than the length of your dragon to allow for even basking.
Generally, a T5 with reflector reaches optimal output at about 12-14'' while a T8 with reflector reaches optimal output at about 6-8''. Mercury vapor bulbs vary depending on manufacturer and wattage. The 26w coils have output similar to a T8 and the 13w coils aren't really powerful enough to provide adequate UVB at safe distances.
Taterbug put together a really great site that describes this in better detail. It's worth checking out if you're interested in learning more about lighting setups.
https://sites.google.com/site/thelizardmadness/lighting-guides
https://sites.google.com/site/thelizardmadness/photogradient