August 2004

Articles

- Living in their Habitat:
By Mary Lovein

- Lighting for Chameleons – Part # 1:
By Andy Beveridge

- Introduction to Common Chameleon Plants for New Owners:
By Brandy Snow

- Scientific Input on Captive Management Issues. An Interview with Dr. Gary W. Ferguson:
By Chris Anderson

- Another Color: Praying Mantids
By Leah Kroo

- Questions and Answers:
By Chris Anderson


Link to this article through this URL at: http://www.chameleonnews.com/lighting1.html



Lighting for Chameleons – Part # 1:

By Andy Beveridge

We all (hopefully) know that a suitable source of UV-B light is an important factor in keeping a healthy chameleon. In an ideal situation we would provide this the same way they get it in the wild – by giving them access to natural unfiltered sunlight but other practical considerations such as our local climate forces many of us to keep our chameleons under artificial lighting for at least part of the year.

In the past there has been relatively little choice of specialist lighting for this purpose but this situation has slowly improved in recent years such that we now have available several different products of at least three fundamentally different types. Yet despite the availability of these products there has been relatively little research publicly available to allow us to make educated choices in chameleon lighting.

More research and information is still very much needed but the aim here today is to try to provide a small summary of what we do know or can reasonably assume about the currently available lighting options so that we can make better informed decisions. This article alone will not tell you everything you need to know about UV-B light sources; nor will it provide detailed stats about UV-B levels from various lamps. The intention is more to provide you with something to think about when setting up lighting in you next chameleon habitat and hopefully draw your attention to the bigger issue of lighting in general, not just UV-B.

The thing we call light is just a small part of the range of electromagnetic radiation produced by our sun. Much as sound of different frequencies has some different properties so too does EM radiation of different frequencies. Rather than considering frequency of EM radiation it is generally more convenient to consider wavelength. The wavelength is literally the length of a single ‘wave’ cycle of the radiation and for light is usually measured in nanometers (one nanometer is 1 thousandth of a millionth of a metre – yes, that’s very small). The sun produces a whole range of wavelengths. Much as the human ear is sensitive to a limited range of sound frequencies, so the eye is only sensitive to a limited range of light frequencies but there is much more there than the part that we can see. Just as there is ultrasonic and subsonic sound so there is ultraviolet and infra-red radiation or light. What we commonly think of as UV is light of wavelength short enough to be just beyond the visible range and infra red is light of wavelength just too long to be visible.

You don’t commonly get lamps that produce just UV so if we’re going to look at light sources for chameleons it makes sense to consider the whole spectrum of light they produce. For convenience we classify the different types of light very roughly according to their properties.

According to multiple sources (NASA, FDA, and others) the wavelengths of the UVA, UVB and UVC regions are: UVA 400 nm - 320 nm, UVB 320 nm - 290 nm, UVC 290 nm - 100 nm

The most obvious component of the light sources we use is the visible light which we can see with our own eyes. To us mammals visible light has wavelengths ranging from blue/violet (~400nm) to red (~700nm). We tend to take that range of light for granted but it has important effects upon colour perception and if ever there was an animal keyed to colour perception then surely chameleons are it.

So we would probably deduce that a reasonably “white” source of visible light is a good idea so that our chameleons can see the whole range of colours in their environment and in each other. That does seem sensible but there are a couple of factors that complicate this somewhat.

1) Spectral intensity vs perceived intensity. Our eyes detect only three basic colours (R,G,B) with each receptor type sensitive to quite a broad range. So light that has three bright peaks of red, green, and blue will appear the same to us as light which has a spectrum that is continuous across the whole range. If chameleons see light the same way that we do this may not be important but there are definitely differences in the way chameleons see; for example…

2) Chameleons have a wider visible range than us humans. Along with insects and some birds it is a pretty safe bet that chameleon vision extends into the ultra-violet. UV-A (commonly referred to as “blacklight”) ranges from 400nm down to about 350nm. Regular household lighting tends to only provide the colors that we humans can see so using it for chameleon lighting would be like putting red light bulbs in your house. We would certainly regard that as unnatural but would that red lighting affect your behaviour? There have been plenty of studies showing that full-spectrum lighting has important psychological and physiological effects on people. We don’t really know for sure how this applies to chameleons but there is certainly anecdotal evidence that UV-A affects the day to day behaviour and breeding potential of both birds and chameleons.

Beyond UV-A there is still more light which is important. From approx 350nm down to 250nm we have UV-B. This is probably the area which we hear most about because

UV-B light on the skin of animals (including chameleons) catalyses the conversion of 7dhc to previtD3. VitD is important for normal uptake of calcium from the gut. There are other factors (dietary calcium, phosphate, minerals like Mg or Mn or Zn, ingested phytate and oxalate from plants etc etc) but basically without Vitamin-D a chameleon will have problems forming healthy bones even if they are getting plenty of calcium in their diet. The effects are very well known to chameleon keepers because early indoor cham keeping was plagued with young chameleons with the malformed and low density bone problems that are characteristic of MBD.

Vitamin D can be provided using dietary supplements but in practice this is not so easy because excess vit-D is quite toxic. Vitamin toxicity and supplements is a complex subject worthy of another article so for our purposes here let’s just style='mso-spacerun:yes'> accept that it requires more care than most of us would consider practical and stick with UV-B as our main provider of Vit-D.

The range of light we typically classify as UV-B is quite broad, covering 320nm down to 280nm. Given that this same range of UV light is responsible for sunburn (which scientists refer to as “erythema”) it should not be surprising that the effects of this radiation have been studied in some considerable depth, at least in human skin.

There is plenty of scientific evidence that the production of pre-Vit-D3 from 7DHC is catalysed by a very specific range of UV-B wavelengths so it’s not the whole UV range that is relevant, just the portion from 290-310nm (with the optimum at 295-300nm). It also seems that the prescence of light of wavelengths below 290nm or above 310nm can contribute to the breakdown/regulation/removal of Vit-D3 so the effectiveness of a light source is not just related to the total amount of UV-B. To complicate things still further, the wavelength ranges which we classify as UV-B are not cast in stone and different sources may use different approximate values for their ranges to suit their purposes. As a result of these factors you can see that terms like “5% UV-B” are actually very vague and don’t tell you very much about a lamp’s potential for promoting vit-D synthesis in your chameleon.

Sunlight:Before we start looking at different lamps let’s take a closer look at sunlight and see how it stacks up regarding the factors we have already identified. A wide range UV-visible spectrometer shows us a measurement of the amount of light at different wavelengths in sunlight. This particular sample is what you get aiming directly at the sun on sunny October day in the UK. We’ll start by looking at the right side of this graph and will work towards the left just so we can leave the most interesting UV ranges to last.

Infra-red (>700nm). In nature IR is generally noticed as heat absorbed by dark surfaces. We’ve probably all seen chameleons basking? They darken their skin and turn maximum surface area to face the light. For millions of years it has been that an arboreal chameleon’s only source of heat is where the light comes from so a chameleon’s expectations of heat are closely linked to their view of light and chameleons rarely notice a heat source if it is not also a bright light. That is why we provide a basking lamp, not a basking heater or a hot rock.

Visible (400 to 700nm): By far the majority proportion of light reaching earth from the sun is in the visible range (mark 700nm to 400nm on the graph). Note also that the spectrum is continuous across the whole range. You may be curious why it’s not a completely smooth curve? That’s because chemicals in the suns corona and the earth’s atmosphere have characteristic absorption bands that remove some of the energy. One of the most important of these is ozone (see below).

UV-A (320 to 400nm): Again, a continuous spectrum, but at lower levels although still plenty high enough to make a big difference to animals that can see UV-A like chameleons, birds, and insects.

UV-B (290 to 320nm): Still a continuous spectrum but at much lower levels than UV-A or visible. Of particular note here is the green line at 315nm; only the light to the left of this marker is useful for Vitamin-D synthesis. It seems that the natural levels of UV-B responsible for vit-D are so low they look almost below the scale in comparison to everything else! This should give you the idea that maybe chameleons don’t always need a huge amount of UV – it’s getting the right amount that is tricky.

UV-C (<290nm): Whilst small amounts of the right wavelength of UV-B are beneficial because of its effects on Vit-D production, UV light at 250-290nm will cause the breakdown of the pre-vitamin-D3 (and also DNA!). Not only that but UV-C exposure tends to burn very nastily and cause cancer in exposed skin. Artificial UV-C sources are used to sterilise surgical instruments and aquarium water. Fortunately for us the wavelengths below 290nm are filtered out by ozone in the Earth’s atmosphere leaving us, at the earth’s surface, with the range of radiation in the graph above.

So that’s it, right? Sunlight has UV-B which the chameleon needs a certain amount of in order to make vitamin-D so it can absorb calcium? Ah, if only it were that simple – we’d just buy the right lamp (which as you will see is actually not so simple) and then we’re all sorted. As with most natural things, once you start to look at them more closely the reality is a bit more complex.

Time of day: Unlike our lamps, the sun is not constant throughout the day. Sunlight intensity is greatest at noon in the middle of summer when the sun is closest to directly overhead. At other times of year and other times of the day the shallower incident angle of the sunlight means that the overall intensity of the light and the amounts of UV-A and UV-B are greatly reduced. The same goes for more northerly or southerly latitudes, the further from the equator we go, the more light intensity is lost. class=GramE>So although a wild chameleon gets enough light to see by for 12 or more hours of the day, the peak for heat and UV-B will occur later in the day. This emphasizes the effects of behavioural differences, the times at which a chameleon typically basks or hunts will have considerable impact on the amount of UV-B it receives. This is particularly relevant when you consider that many chameleon species bask mainly in the morning (to warm up before they go looking for food) and during much of the rest of the day they may be in shaded forest.

That is direct unfiltered sunlight. Transparent glass or plastic is generally designed for us to see through it. Unfortunately such materials usually block almost all of the UV-B such that a chameleon sunbathing behind a window is getting little benefit besides a nice warm feeling. I can show you more graphs that demonstrate the effect of a glass or polycarbonate window but perhaps that is also best left for another article as we still have a lot of ground to cover.

Species and Environment: Different species of chameleons may come from radically different habitats. A wild chameleon such as F. pardalis in a hot sparse sea-level environment will typically receive a lot more UV-B than a species which lives in a highly humid dense forest environment halfway up a mountain such as C. montium. It should not be surprising that F. pardalis is adapted to withstand intense UV-B whereas C. montium is adapted to make the most of low levels of UV-B. It therefore seems pretty obvious that their natural tolerances to UV-B would be quite different.

It is quite possible to have too much UV-B.

This article originally arose from chameleon keepers discussing a scientific research paper recently published by Gary Ferguson et al. Amongst other issues the data in that paper seems to indicate that overdosing is possible. This would also seem to support the anecdotal evidence of a few chameleon keepers. Based on this info and the lack of any evidence that that excessive UVB exposure has any beneficial effects, it would seem reasonable to try to avoid excessive UV-B exposure. Firstly, the vit-D synthesis reaction we have been looking at can only absorb a certain amount of UV-B and everything beyond that can actually do harm. Excessive UV-B has the potential to severely burn (erythema?) exposed skin. Skin which has acclimatized to bright UV-B will adapt to block some of it and can tolerate much more than skin which does not see signifigant amounts. In human’s we call this a suntan and it is notable that this higher tolerance is visible as a difference in skin pigmentation. This goes for chameleons just as it does with humans so clearly more UV-B is not necessarily better, particularly for chameleons which do not regularly see a lot of UV. In long term exposure skin will adapt to deal with the amount of UV-B it typically gets to see. This is worth considering when moving chameleons outside as it seems they can easily overcook themselves if they are not acclimatized. There is a saying that “only mad dogs and Englishmen go out in the midday sun” (and the English are indeed pretty good at sunburn) but take it from us that English chameleons normally starved of real sunshine can just as easily suffer from sunstroke the first time they spend a whole day outside in summer.

Behavioral factors. It’s a chameleon, it knows what to do with sunlight right? Well, not always. For a start, notice that the numbers you have been seeing are from looking directly at the sun. If you turn away from the sun the figures would be very much lower. Under normal circumstances a healthy chameleon would position itself to take maximum advantage of the sunlight as required. The rest of the time it would be following basic urges to look for food etc and during that time it’s exposure to direct sunlight could be very much lower. That sounds simple enough but consider how this behaviour is affected by your cage and feeding patterns. It is not normal for a chameleon to be confined to one small space. What will a chameleon do if there is nothing new to explore. Consider also that if your chameleon is ‘given’ food rather than being encouraged to natural hunting/searching behaviour what will it do instead? Will the fat chameleon sit and sunbathe in the nice warm light all day? I know I certainly would. Not only would such a sedentary chameleon get rather fat but it would also probably receive a much greater exposure to direct sunlight and UV-B than it’s hungry wild counterpart. Which is the healthier?

Artificial light sources: OK, so that’s the sunlight and it’s a bit more complicated than you might have expected but you get the general idea of the qualities of the light and the other related factors that affect the way your chameleon benefits from it. Hopefully that has at least provided some useful food for thought. If you are keeping chameleons outside you probably don’t need to read much further. If you are keeping chameleons indoors then it’s important to choose a suitable light source and to use it wisely. In the next part of this article we’ll look at the most common lighting technologies that we might buy for our chameleon: Fluorescent, Mercury Vapour, Metal Halide etc. We’ll be providing a little information about the amount and kind of light the lamp produces and other relevant issues bearing in mind what we have already discussed here.

Literature cited:-

Ferguson, Gehrmann, Karsten, Hammack, McRae, Chen, Lung, and Holick. 2002. Do Panther Chameleons Bask to Regulate Endogenous Vitamin D3 Production?


Andy Beveridge


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