Mercury Vapor Bulbs are the pinnacle of UVB light. They are mainly great for daytime reptiles and produce a very good amount of UVB. Much higher than those Zoo Med or Exo Terra UVB bulbs. You'll see many turtles and tortoise owners use Mercury Vapors due to the fact that it's an all in one unit for emitting UVB and heat.
A 160W mercury vapor bulb can bring area up to 100F at a distance of 2 feet. Reptiles may like to bask in UVB, but UVB is also harmful for plants so beware using mercury vapor on plant life.
I found this brand to be cheap and long lasting
Welcome To ReptileUV - Mega-Ray® UVB lamps for reptile lighting worldwide
However, all UVB bulbs diminish in radiation through time and you should change them every year.
Mercury Vapor bulbs you buy from major brand name pet companies will be $10+ more per watt than a ReptileUV mercury vapor bulb. I use them on all my turtles.
Ethan, what do you know about the Xenon puck lights? How are they in regards to uvb? they definitely emit some good heat
I believe Xenon light has a wavelength between 150-200 nm which is in the realm of UVC -highly dangerous radiation that have harmful effects to living things in general.