Lighting is yet another issue up for debate for hognoses!
Under tank heaters certainly are convenient and relatively energy-efficient. Unfortunately they are counterintuitive for most herps. Specifically hognoses, Dwight Platt in his study found that hognoses burrow into the ground to escape high heat. So for hognoses it doesn't make sense for them to dig down only to find it warmer than on the surface, the exact opposite than in nature. I strongly believe that under tank heaters can be used as a supplement, especially as a night heater. However, a "full spectrum" incandescent is the ideal heat source for hognoses. This provides heat from above that a diurnal snake would appreciate.
It is physically impossible for incandescent bulbs to produce UVB, so full spectrum only refers to its ability to produce UVA. For the most part this is useless for UV requiring reptiles, but I believe it has its place with hognoses. There is abundant literature and personal accounts of all taxa of vertebrates behaving more naturally when exposed to full spectrum light (humans are not exempt from this phenomenon). I believe that with the ubiquity of feeding problems associated with captive hognoses, and their diurnal habits, they should be provided with at least a full spectrum incandescent bulb. It stands to reason that PERHAPS there would be less problems with anorexia among hognoses if there are provided with a simple ingredient that is proven to positively affect animals. After all, we're talking less than $10 a bulb! Of course there are many snakes that the barely get ambient light in their rack systems and do just fine! However, in my experience with snakes, whenever there is a problem the first thing I do is yank it out of the rack and put it in a tank with full spectrum lighting. I personally have not seen too much of a change in health/behavior with this method, but my sample size is relatively low.
According to Dr. Frye's reptile medicine books, snakes do not need UVB because they get vitamin D from the livers of their rodent prey. Keep in mind this has huge implications for snakes that do NOT eat mice. For example, I insisted upon putting a full spectrum Mercury vapor bulb on a rough green snake exhibit. The thinking is that these are diurnal snakes that typically have strong exposures to the sun, and don't have the benefit of mouse livers for vitamin D. In general however, UVB is only an absolute requirement for turtles and lizards.
Unless you have your snake container is outside with large mesh for containment, there is no such thing as ambient UV. Supposedly glass will naturally filter UV, and when does are also manufactured with additives to further decrease UV transmission. So don't count on ambient light in your house to provide ultraviolet light.
This is a good time to point out something about full spectrum products. I believe that the only way to go nowadays is with Mercury vapor bulbs. Most of you of heard about the high failure rate of the self ballasted Mercury vapor bulbs on the market today. There are alternatives at www.reptileUV.com. I have personally spent over $1000 on their products and I have a UV meter to prove their effectiveness. I can't say enough good things about their products and their customer service. If any of you reading this post have reptiles that require ultraviolet light, these units are well worth their money. Even florescent bulbs are useless relative to these externally ballasted Mercury vapor bulbs!
I highly recommend the following article:
http://www.austinsturtlepage.com/Articles/guidetolighting.htm
-----
"I know the human being and fish can coexist peacefully."
Governor George W. Bush, Jr.
"Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us."
Calvin and Hobbes (Scientific Progress Goes 'Boink', 1991)
