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[NicoleRussell]

Iguanas and Artificial Light (part 3)

However, its not just UVB, the ultraviolet we need to supply for our animals must be “useable” UVB, in other words, in the “D-UV” range. How can we measure and be confident that we have supplied our creatures with ample amounts of D-UV? By far the most reliable method is to test specifically for blood levels of 25-HDCC (wild iguanas have levels of 175–275 nmol/L of this form of D3 in their blood). This test can be performed by with the help of a qualified veterinarian (see reference below) and is the final say on whether we have provided optimum husbandry for our iguanas. This is much more reliable than using a standard blood panel test (which measures only calcium and phosphorus levels that can and are very deciving). Even iguanas that have what appear to be good blood panels have been found to be on the low end of the active 25-HDCC level. This helps to explain why iguanas in the wild can drop 20 ft out of a tree and hit the ground running, whereas stories of captive Green Iguanas falling 5 ft and ending up with compound fractures are common.

Just what kind of ultraviolet levels are these creatures exposed to in their natural environment? The standard for measuring intensity of the UV spectrum is read in microwatts per square centimeter (µW/cm2). The USDA recently did a study with an Ultraviolet Pyranometer and found readings of UV-B in Florida on June 1st that reached 450 µW/cm2 (remember, however, that only a certain percentage of this falls into our “usable” D-UV). Hobbyists have the ability to take their own UV-B readings with a simple hand-held ultraviolet radiometer from Solarmeter (model 6.2). The measurements taken by the USDA are extremely close to the readings that I have been taking for the last 4 years in a study of reptile lamps and I have used this as a constant for meter calibration.

Although iguanas may not be exposed to as much as 450 µW/cm2 on a continuous basis, they will spend several hours a day exposed to relatively high numbers, generally in 150-250 microwatt range. My studies, as well as those of others, have found that, even in the “deep” shade, global UV-B readings reach 30–50 µW/cm2, but the readings are as high as 250µW/cm2 (in the shade). These numbers give us an idea of the minimum and maximum ultraviolet B exposure levels in nature.

Interestingly, another study has proven that D3 biosynthesis is a naturally self-limiting process. Without getting too technical, this “safety valve” ensures that toxic levels of vitamin D3 are not created, and that the excess is broken back down into inert ingredients (but please see the references at the end of this article). Basically this means that as long as we do not expose our iguanas to any more UV than that to which they are exposed in their natural environment, we will stay within safe perimeters. Also it has been shown that reptiles will regulate the exposure to UV to fulfill the need of D3 biosynthesis. It is important that reptiles in general have the ability to remove them selves from the UV source as well as heat this process of self regulation.

Two styles of reptile UV-B bulbs are available. One is the fluorescent tube and the other is the mercury vapor (MV) reptile lamp. Both style lamps use the heavy metal mercury as a catalyst for producing ultraviolet radiation. An electrical charge passing through liquid mercury excites the molecules until they vaporize (when the mercury cools, it resumes liquid form). In the fluorescent tube, the mercury must combine with high-grade phosphorus to achieve the ultraviolet results.

Over the past four years, I have studied failure and decay rates of mercury vapor lamps and conducted a general study of the major brand fluorescent tube reptile bulbs. I am constantly asked if I have tested a certain fluorescent brand bulb by individuals who have seen them listed inexpensively — in spite of the fact that, for many years, I have been telling people that quality UV is not cheap (unless we’re talking about the great and wondrous sun). In a recent conversation with Voltarc Technologies, one of the largest manufacturers of reptile fluorescent bulbs in the nation, the engineers confirmed the fact that money buys UV.

Production costs rise with more exacting specifications (how much UV-B and where precisely it is to be delivered). In order to build a tube that will provide not only high UV-B readings, but one that will generate output in the useable 290–300 nm range, manufacturing tolerances have to be very precise. Two different fluorescent tubes can emit equal amounts of total UV-B, yet one will do a much better job keeping your pet healthy than the other (even though both bulbs might have been manufactured by the same company, but for two different distributors’ specifications).

The best florescent tubes tested emit 12–15 µW/cm2 at 12” after initial burning. A variety of good fluorescents (as well as some absolutely terrible ones) are on the market, but ZooMed 5.0 is built to the most exacting tolerances according to all of the manufacturers with whom I have spoken. It should be noted that research has shown that using good reflectors behind fluorescent tubes can up to double the UVR iridescence. Through the work of the Yahoo Meters group, we are finding there are other florescent tubes stepping up the plate in respectable UVB production.

The other choice in artificial UV is the mercury vapor reptile lamp, which comes in a variety of styles and wattages. Anyone who has been involved rehabilitation work and has used MV lamps, has seen the effects of these bulbs compared to even the best fluorescent tubes. Why is this the case? Do they emit huge amounts of UV? Are they reliable? Is one brand better than another?