Which UVB fixture is preferable?

[CameronJayBauer]

Honestly, I don't think anyone can truthfully say how long is the useful life with any sort of realistic accuracy. You'll encounter the typical "six months replacement" regurgitation, but I don't actually think this is based on any empirical evidence whatsoever. There are two main problems that would hinder anyone to give an accurate answer: very few actually have the appropriate equipment to realistically measure their output (I've seen a wonderful piece of equipment and for some reason I can't even get the manufacturer to give me a damned quote on what it costs), and no one really knows how much UVB is essential to not only promote good health, but ensure it.

Now, having said this, I have some anecdotal evidence that, contrary to what is often said (even by myself), seems to point in a direction many would argue against (including myself). Years ago when dinosaurs roamed North America and I was just starting out my first steps in research with tegus, my supervisor had brought me my initial collection of something like 35 baby tegus and had me set them up to his guidelines. Now, I was no where near as knowledgeable (or confident) as I am now, but even them I was "well, I wouldn't set them up that way, but you're the boss". Basically, they were kept in large fiberglass bins with brooder heat lamps (the big red bulbs), being fed a ground meat mash with chopped veggies and vitamin/mineral supplementation. It wasn't too long before some started showing the early signs of calcium deficiency (muscle tremors). Called in our departmental veterinarian, he concurred, we gave them some shots of calcium (and I think vit D3), tremors went away. Then came back. So we tried mixing up the shots, including other vitamins and such associated with the whole calcium regulation pathways, each time succeeding in driving off the tremors only to have them return later. We really analysed what I was feeding them and were quite certain that mineral and nutritional needs were being met. And the numbers of tegus affected kept growing. Being somewhat analytical and wanting to figure out what was going wrong, I started dividing up the tegus according to the severity/repeatedness I was observing. Before long, had run out of suitable housing in our lab, and so did what I usually did: brought in my own stuff to completely separate all the affected animals. Set them up individually, and before long, started to see a pattern. Some of the tegus kept developing tremors, some got better and we never saw tremors in them again. Looking at who got treated with what, there was no clear pattern to indicate which treatment we'd tried seemed to be working. Until it dawned on me - the ones that were no longer exhibiting tremors were ones now being housed in MY terrariums with MY lighting.....fluorescent bulbs with UV output. Here's the kicker: this was BEFORE the selection of bulbs we have now, and I certainly didn't bring in brand new bulbs at my own expense, these were old Vitalite bulbs, some before the "patented twist" line, that I had kicking around, wasn't using anymore as I thought they were likely "spent". Some of these bulbs were likely 5-7 years old, and the Vitalites never had the intensity we now have in reptile lighting. These old bulbs clearly had enough UVB to correct the problem.

Here's the issue, though. Even with this story behind me, this is NOT a statement that any old bulb will do, or that old bulbs will continue to produce adequate UVB for years. Only that in this situation, it was enough to adjust a "bad" situation and make it better. Since then I've learned a lot more and understand the situation better than it appears most do. Most of us are aware that UVB helps the calcium metabolism pathway. Some understand that what UVB does is convert pre-vitamin D3 to bioactive pro-vitaminD3 (it's far more complicated than this, but this is suitable for what we're talking about). Fewer seem to understand that vitamin D3 is a lipid soluble vitamin (unlike most), and therefore can be sequestered and stored in tissues, and as such can thereby reach hazardous, toxic levels (water soluble vitamins we just pee out). This is because surprisingly we don't have an innate, biological method of regulating our vitamin D3 content. What very few seem to realise (including the human health practitioners that go on about how many units of vitamin D3 you should intake every day) is that once the vitamin D3 levels reach a sufficient concentration in our plasma and with sufficient intensity of UVB, that the pro-vitamin D3 is FURTHER converted to two inert forms that are apparently non-toxic at any concentration. So we need some UVB to photoactivate vitamin D3 into a usable form, and then we need MORE UVB of sufficient intensity to properly regulate Vitamin D3 levels.

Short'n'sweet: A suitable fluorescent bulb can likely produce UVB of sufficient intensity to activate some vitamin D3 for quite some time, but to produce enough UVB to properly regulate the vitamin D3 ........... no one really knows what intensity is necessary or how long the various bulbs can maintain that intensity.

I seriously love your background knowledge of tegu research. This is an awesome bit of information. Regardless if we don't have a concrete conclusion on the amount of UVB necessary, this alone gives me a far better understanding of the role UVB lighting has, thank you.

Do you have any opinions regarding an unhealthy amount of UVB exposure?

 

[viejo]

Thank you for the detailed reply. This mirrors my thoughts on UVB as well. Good to hear that overdosing D3 should apparently not be a problem for the tegu or even myself.

 

[Roadkill]

I've read 6 months for uvb bulbs.

That's what I'm getting at, though. People keep saying this and regurgitating it, it gets accepted as gospel, but it's based upon.......what? Who first made this claim and based on what empirical evidence to support it? Near as I can tell, it's the sellers (I would say manufacturers, but Exo-Terra/Zilla/several others just purchase from somewhere else and then relabel), and considering these same sources didn't prevent the eye issue photokeratoconjunctivitis that has become associated with the compact fluorescent bulbs (but really should be associated with all bulbs manufactured during a certain period)....who's to say it isn't a sales gimmick? At the same time, who's to say they even last 6 months? This is what I'm stressing here, we really don't know, and with a lot of the equipment people use (including myself) to get a better idea, we really don't wind up having a better idea.

Good to hear that overdosing D3 should apparently not be a problem for the tegu or even myself.

Hold on, that's not what I said at all. Yes, you and your tegu can overdose on vitamin D3 as it is a lipid soluble molecule, your body will sequester it and store it and can do so to a point where it can become toxic and you can suffer hypervitaminosis. In fact, many people using the usual erroneous logic of "if a little is good, a lot must be better" have caused calcification of soft tissues in their reptile pets by oversupplementing with calcium and vitamin D3. What I have said is that UVB of sufficient intensity helps to regulate the vitamin D3 levels. This is the problem, though, we really have no idea what that sufficient intensity actually is. My own experience is that it doesn't take a lot of UVB to "create" a decent level of bioactive vitamin D3 to promote health. This is not to say that that minimal level will also regulate healthy levels of vitamin D3. If you understand chemistry and reaction rates, it comes down to an interplay between the concentration of the substrate being changed (in this case, vitamin D3), and the intensity of the wavelengths inducing the change (in this case UVB). Giving vitamin D3 supplements should always be implemented with UVB exposure as well. If we consider that full sunlight is a much greater intensity than any artificial UVB source we have ready access to for our pets, it seems safe to say we should go for the highest ratings we can afford. However, the flip side to this is unlike what most people seem to think, the vast majority of reptiles do NOT spend all day basking in full sunlight in the wild. Even large tegus are living in an environment where all day full exposure to the sun would kill them. They come out to bask first thing in the morning (maybe an hour or two) and again later in the day before they retire to the burrow for the evening (maybe half hour to 2 hours). The rest of the day they are either asleep or avoiding that intense sun. These basking sessions of high intensity UVB are apparently sufficient for proper vitamin D3 regulation. This is why for set ups I recommend a combination of UVB sources, fluorescents to provide a gentle ambient UVB source, and mercury vapor bulbs to provide a high intensity UVB basking site.

Do you have any opinions regarding an unhealthy amount of UVB exposure?

yes and no. I can't say anything definitive. If you go looking through the scientific literature, way back, you will see reference to snow blindness in Arctic peoples and polar explorers. This was attributed to too high intensity of UVB at those latitudes. Hence, why with the somewhat recent photokeratoconjunctivitis people were observing in pet reptiles, that it also became associated with too high intensity of UVB. My question to this, though, is I don't think anyone has ever tested this idea. I'm not saying it isn't possible, just that I don't believe it has any concrete evidence to back it up. My own hypothesis is that what is likely happening is actually UVC exposure (but will fully admit not having any evidence either). However, going with the idea that it is possible to have too high of an UVB intensity that could be unhealthy, this is why I suggest a fluorescent for weak ambient exposure, high intensity UVB/basking bulbs for short term exposure.

 

[Walter1]

If all of this doesn't make us aware of variable affecting what we buy for light vs what the animal needs and must avoid, it is probable that UVB requrement varies among ages, body sizes, and sexes, not to mention gravid or not. AND variation exists within these categories. I bring this up as a matter of variables to consider. Somewhere, but, as Roadkill notes, who knows quite where, is probably a decent target to shoot at around which differences occur for UVB needs and limits. Manufacturers selling these lights do not proovide that useful nugget for any heliotherm, nor do they seem to provide data on longevity or side-effects.

 

[Roadkill]

While it's quite likely a lot of those variables do have an influence, I imagine (except during breeding season for females) many of them don't show that big of a variance. The one that I think would have an even bigger influence is colouration. Melanin is not just colour, it is a natural sun blocker. Considering we see this colouration even in shed skin, then it means that pigment is right at the surface, blocking sun (and particularly UVB) from accessing deeper tissue, and thereby inhibiting vitamin D3 activation/formation. The more black they are, the more UVB exposure they will need, and vice versa.

 

[Justin]

The reason I read as to replacing uvb bulbs is that the uvb output diminishes over time.

 

[CameronJayBauer]

The reason I read as to replacing uvb bulbs is that the uvb output diminishes over time.

Right. But as Roadkill said in detail, we don't know how much diminishes, or over how long of a period. As Roadkill had said, bulbs that were around 5-7 years old were still able to bring their tegus back to health...
The bottom line is that we can't tell how much UVB is necessary and how much is lost over time.