Licht-im-Terrarium: Literaturdatenbank
Licht-im-Terrarium: Literaturdatenbank |
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Highfield, A. Major new research on basking lamps. . Retrieved July 1, 2012, http://www.tortoisetrus ... opic.php?f=3&t=8079 Added by: Sarina (2012-07-12 17:19:52) |
| Resource type: Web Article BibTeX citation key: Highfield View all bibliographic details  |
Categories: Englisch = English Keywords: Thermoregulation = Thermoregulation Creators: Highfield |
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| Abstract |
We are now preparing this very complex work for publication, but over the next few days I will give you all a preview of some of the most important findings. The images below illustrate one of the techniques we have employed to investigate this area, it is an infra-red thermography image. The basic image only gives a rough idea of the true extent of data these thermographs include. When read on the computer, a whole range of analyses are possible. These have enabled us to directly compare hundreds of examples of tortoises a) under basking lamps and b) basking under natural conditions, and to identify key differences in patterns of heat distribution. This is an example of a tortoise under a typical incandescent basking lamp, with a background temperature of 22C: Compare to a wild tortoise, imaged at exactly the same background temperature:  Multiple factors affect the precise heating pattern obtained from lamps, and also the time-scale involved in distributing the heat from the lamp through the tortoise's body. These include: a) Size/Mass of the animal b) Power and physical size of the basking source c) Beam distribution (e.g. spot vs. flood) d) Background (ambient) temperature From the above images, you will note that the heat distribution is highly concentrated in a relatively small area of the carapace. This is a very typical situation with many basking lamps, and becomes more intense as a) the size of the tortoise increases and b) as the power, distance, and beam concentration changes. In short, a small lamp positioned close to the tortoise will produce a more concentrated effect that a large, wide-beam lamp positioned at a greater distance. What matters very much is the relative size/power of the lamp to the animal. So, a 50cm juvenile will respond quite differently from a 30cm adult under an identical lamp. This spot heating effect is very different from the heating effects observed in the wild. It has serious implications for everything from natural D3 synthesis to digestive processes. The effect typically seen under lamps is highly localised heating (sometimes over-heating to the point of trauma) of a small portion of the animal, where under natural conditions the distribution is much more even and with less dynamic range. In short, the differentials are more extreme in tortoises under artificial basking sources. The full implications of this will be discussed in detail in our report. I would also stress this is just one aspect that has been investigated. There is a further aspect that is just as critical. Further examples. A pair of tortoises in the wild just beginning to graze after emergence, the sun angle was quite low. Note the extremely even heat distribution, especially on the legs and head. This is important, as it is in these areas where D3 is produced (by heat action on sterols in the skin). If the skin is too cool, then D3 production falls off dramatically, even if adequate UVB is available:  This is the result after extended basking with a 160w MV lamp with flood beam pattern placed on a slight angle in a trial to see if the sun angle could be replicated:  While limbs closer to the lamp attained acceptable temperatures, those further away remained quite cold, and again the uneven heat distribution on the carapace is immediately evident. This illustrates one issue with these kinds of lamps - the beam distribution, even with a 'flood' design still appears as a small spot source, closer in effect to a 'searchlight' beam than to a true flood or diffused source. All tortoises here were relatively small and were comparable in size. With larger animals the effect is even more pronounced. This very dramatic image graphically demonstrates the effect of a typical 100w basking lamp positioned above a tortoise with the object of attaining 30 degrees Celsius on the carapace with a room background temperature of 16.9 C (as often experienced indoors, in winter, in Northern Europe).  Only a relatively small area is heated, while the remainder of the carapace, and skin areas, remain below 18C. Even though UVB levels from the lamp appear sufficient, the reality is that their effect is very limited due to the poor distribution of heat to the extremities. Even a keeper using a UV meter + thermometer could misinterpret the data in this example, unless they took multiple spot readings from numerous positions on the animal. In addition, this image also gives some insight into why thermal burns from lamps are especially common in very large tortoises (Leopards, for example, under heat lamps). In an effort to raise their core and extremity temperatures to desired levels, they effectively "cook" the surfaces closest to the lamp, attaining dangerously high levels in a small area, while continuing to remain far too cold elsewhere. Due to the mass of larger animals, if the background temperature is low, it will be impossible to obtain even heating throughout the body. The heat will be concentrated in one small section and the animal will continue to bask, despite that area suffering thermal trauma. ############################################################################## Hi, Andy. This is a fantastic piece of research - are you submitting it to a peer-reviewed journal? Andy, another factor I'd like to add in, is the difference between the infrared radiation from sunlight and that from a basking lamp and that from a ceramic heater. Sunlight emits short-wavelength infrared (IR-A) which is filtered by the water vapour in the atmosphere. So it has been "drained" of energy in the wavelengths best absorbed by water.... in other words, the wavelengths which heat up water most strongly have already been removed from the sunlight before it hits the tortoise. The remaining wavelengths of IR-A penetrate gently and deeply into skin, muscle and bone and can warm an animal -literally - to the core. This beautiful "water-filtered IR-A" is what makes sunlight the perfect basking light.... as Andy says, warming the entire basking animal evenly and deeply. On the other hand, incandescent lamps, halogen lamps, self-ballasted mercury vapour lamps, so-called "infrared" red bulbs... any lamp producing heat and light - also emit IR-A ...BUT.... there is only a tiny distance, usually less than a couple of feet, between lamp and reptile. You'd need maybe a mile of atmosphere to absorb those water-heating wavelengths. So where is the first water those rays from a lamp encounter? Yep.... The water in and around the living cells of the reptile's skin, or in the case of the tortoise, in the living cells of its carapace. This is not natural. I think the effect of this type of "extra" heating of water inside the body should be investigated, as logically it will exacerbate the effect of a small, concentrated beam covering only a tiny portion of the animal's back. I have been trying for some time to avoid all usage of the term "basking spot"... it should be "basking ZONE" and it MUST be at least as large as the entire body of the animal. Finally we come to the other type of heater - the non-light-emitting ceramic heater, or heat plate, or heat mats, etc.... These do not emit short-wavelength IR-A, but almost entirely long wavelength IR-C. Sunlight contains hardly any IR-C. But when sunlight warms the ground, the hot substrate re-radiates the heat in the form of IR-C. (Hold your hand just above sunlit rock and feel this type of radiant heat coming off it). (This answers Joan's query about warmth from the substrate, btw) But IR-C from above isn't normal. What is worse, IR-C does NOT penetrate the skin, muscle and bone like IR-A. So it cannot "warm from inside". All the heat energy is released directly onto the skin surface and the first few millimetres of skin depth. The skin has to absorb all this heat energy, and then conduct it to the deeper layers... a much slower and less efficient process. If the IR-C is very strong, then heat will build up dangerously on the surface as it cannot be conducted away to deeper levels fast enough. (We all know the nasty burning feeling on the skin surface, from standing in front of a fire..) I believe that there is probably a much greater risk of thermal burns in reptiles with this type of radiation, because their basking behaviour seems far more governed by their core temperature than by burning sensations from their skin. I guess this is not surprising really. Because they have evolved under sunlight, which makes as big a basking zone as they could possibly wish, and warms to the core every time without fail and with absolutely no risk of a thermal burn in the process. It is very difficult -almost impossible - to replicate sunlight indoors. My personal viewpoint is that incandescent lamps plus top-quality UVB lamps need to be selected and combined to create a LARGE basking ZONE like a patch of sunlight, with a (UVB + UVA + light + IR-A) all-in-one gradient into shade at the other end of the enclosure. Yes, this means large enclosures! I don't think there's anything we can do about the "water-filtering atmosphere", because a mile of atmosphere between lamp and tortoise is a bit far-fetched, if you'll excuse the pun... but a wide zone with no intense hot-spots should reduce the effect - hopefully preventing actual damage to living cells. Andy - can't wait to see your work in print! Best wishes Frances ################################################################################ Hi Frances, Because this has such important practical considerations for keepers, we are publishing it first in the TT Newsletter, with some abstracts online (including here). Subsequently, some rather more academically-oriented materials will appear, also in a book I am working on. I agree entirely with your thesis that there is something 'going on' with infra-red activity on water molecules. I unfortunately do not have the specialised facilities available (or the mathematical theory!) to investigate that in detail...but... purely on an empiric basis, going by measurements I have taken, I have little doubt that something of that kind must be involved. For example, the 'drying' effect appears to be more pronounced than it 'should be' (if that makes any sense), based on temperatures alone. It really is quite severe. The view that high levels of IR-A and IR-C emissions are directly acting on water molecules in the tissue is an attractive explanation for some of this.... As you know, I postulated the theory that migration of water molecules from scute keratin plays a major, major role in the 'pyramiding shell' issue: http://www.tortoisetrust.org/articles/pyramiding.html The use of basking lamps with high IR-A outputs would certainly contribute to this. I have garnered some interesting historical facts on reptile keeping that tends to show these problems have become worse over the years... coinciding with keeper's increasing uptake of such artificial sources and with increased reliance on indoor husbandry.... not conclusive, but interesting... I have been running various trials with basking lamps to try to establish what precisely happens with respect to humidity in the 'basking zone'. This is merely one example: Image This trial was conducted using a 120w MV lamp at 40cm in an open room (not in an enclosure). Starting humidity was circa 68% (which is quite high). The lamp was turned on at 7.30 am. Humidity under the lamp almost immediately plummeted to below 30%, fluctuated around 20%, and attained a minimum of of circa 17%. The lamp was turned off at 7.30 pm. Humidity very rapidly recovered. Just before 6.00 am the following day, the lamp was turned back on. The results were very similar. From circa 68% humidity crashed to around 20%, and again reached a minimum of approximately 17%.** As soon as the lamp was turned off, levels recovered. Now, 68% is quite a high starting level. Many domestic premises (especially in winter with CH running) are 45% or less. In those cases, RH in the basking zone can fall to levels barely above 10%. This is extremely dangerous, as you know, and will result in chronic dehydration and placing the animal at greatly enhanced risk of renal complications and bladder 'stones'. These are problems that unfortunately, are regularly seen in captive tortoises, especially so in those maintained under very artificial conditions. Must add - I owe you an email! Will respond to that in detail shortly! ** Our recommendation is to aim for circa 50% as a safe general level of RH.Extended exposure to levels below 30% are increasingly hazardous. ############################################################################## This needs to be put on context. It was as recent as 1969 that the importance of UV-B for reptiles began to be recognised (1). It was as recent as 1944 that the entire concept of thermoregulation was identified (2). The use of basking lamps for tortoises did not really become common until the early 1980's. None of this is very long in terms of human knowledge. We are, therefore, still learning about this. We (clearly) do not yet fully understand all of the dynamics involved. No-one does. Lamps have certainly helped in many ways, by providing extra heat and by providing UV-B. However... it is the case that while solving some problems, others are created.... this is rather typical when humans mess around with nature! In my opinion, the 'perfect' lamp for reptiles does not yet exist. All of the commercial lamps have various shortcomings. Some more serious than others. I can't really comment on individual setups because there are so many variables, and in order to really know how they are working you need to measure them very carefully using precision equipment (UV meters, data loggers, thermographic cameras, etc.). Personally, right now, on the evidence available, I would be very wary of all of these lamps. I have tested quite a number over the past year or so, and found problems with all of them, specifically the heat distribution and dehydration effects. These results are easily repeatable. Anyone with access to the right equipment can run similar tests. Unfortunately, I cannot say which particular lamp is "best". I can say that in my view, the less you have to rely on them the better. The best tortoise habitat we ever had in the UK was based on a large polytunnel. That had no artificial light, or heat. Tortoises even estivated in there in summer, and hibernated undergound with consistently good results. They did go outside (as weather permitted) to gain natural UV-B exposure. This was an excellent set-up, and I think hard to beat in that climate. Obviously, not practical for everyone, but certainly the least problematic in my experience from the animal's point of view. (1) Laszlo, J. 1969. Observations on two new artificial lights for reptile displays. International Zoo Yearbook 9:12-13. (2) Cowles, R.B. and Bogert, C.M. (1944). A preliminary study of the thermal requirements of desert reptiles. Bull. Am. Mus Nat. Hist. 82, 265-296. Added by: Sarina Last edited by: Sarina |