Interview With Frances Baines. Part II

For previous session (Part I) click here
5. Your comment of “UVB lamps should be positioned over the basking zone” and “D3 synthesis requires warmth” intrigues me. In your opinion, do reptiles have some perception of the presence of uvb and heat as different entities? Or do they assume visible light means warmth and uvb in one. What is the problem, if there is any, from separating uvb to one end and heat bulb to another end?

Dr. Gary Ferguson and his team have done pioneering studies into the reptile "perception" of UVB, working with Panther chameleons. Their carefully designed experiments do suggest that chameleons, at least, can perceive UVB - or at least, perceive locations where there are higher levels of UVB - since, if they are deficient in vitamin D3, they choose to spend longer in these areas.

Chameleons were given the opportunity to choose whether or not to bask under UVB or UVA lamps in an enclosure where both shady and exposed areas were held at a uniform ambient temperature (about 29C). The chameleons were significantly attracted to the light from both lamps, and the vitamin D3-deficient ones were more attracted to the UVB lamps than the UVA lamps.

This does suggest that they are attracted to light even when it is not associated with heat, and that they can perceive UVB as a separate entity from UVA. What exactly do they perceive, though? They can definitely see UVA, but it seems unlikely, given the properties of the reptile eye, that they can actually see UVB. Maybe they can feel it on their skin; maybe the "feel-good factor" humans experience under UVB, possibly linked to endorphin production, is a faded human version of what a reptile experiences?

But can chameleons perceive light and heat as different entities? We can't really deduce that, because this experiment doesn't investigate the chameleon's perception of heat, at all.

I know of very few studies on reptiles where the components of sunlight have been separated out, to see what choices the reptile will make. Since a reptile must maintain its core temperature between very specific limits for life itself, we might hypothesize that if reptiles can distinguish between them, they would select basking spots based upon the temperature there, rather than upon the presence of light or UV light in the area.

One experiment conducted on spiny-tailed iguanas by Dickinson and Fa (1997) showed that these lizards were all significantly more attracted to an incandescent lamp than to a non-light-emitting heat source or a UV tube, which seems to undermine the theory. Unfortunately, the results are not conclusive, because the temperature under the incandescent lamp was hotter than under the non-light heat source, and much hotter than under the UV tube.

More research is needed! However, part of Dickinson and Fa's study clearly showed that when the choice was between the incandescent lamp and the UV tube, the lizards were primarily attracted to the lamp; they spent comparatively little time under the tube.

If we separate our UVB tubes from our heat lamps, then this is an unnatural state of affairs, which requires the reptile to make a choice it would not need to make in the wild. The captive reptile in this situation cannot absorb UVB and bask at the same time. Even if it "knows" it needs UVB, the vital necessity of maintaining a suitable body temperature seems likely to be prioritized over UV absorption, which could well be much reduced as a result. But someone needs to do the experiments, to find out whether this is indeed the case.

6. So many elements need to be considered in simulating light in captivity to be as close as possible to natural light. What about the effect of moon light to reptiles? Is this something that we might, in the future, be interested to simulate as well even for diurnal reptiles such as chameleons?

Here's what seems to be a popular view: "Reptiles can't see red light, and infra-red lamps aren't very bright, so they can be used 24/7 as a heat source. Alternatively, moonlight is blue, so deep blue lamps can be used to simulate moonlight. Moonlight is natural and won't affect the reptiles. The lamps look really nice to me, and enable night-time viewing."

The only part of this which is true is ". The lamps look really nice to me, and enable night-time viewing." I am convinced that using lamps at night is solely for the benefit of the human owner.

Firstly, reptiles can see red light. It is true that some reptiles lack a "red" cone in their retina; but, so do colorblind humans, and red light isn't invisible to them, either. Red looks bright; it's just not a distinctive color to them. Chameleons do have a "red" cone however, and can see every color in the spectrum, from UVA to red.

Secondly, moonlight is NOT blue. It's sunlight reflected off a huge light gray lump of rock - it has all the colors of sunlight - it's a slightly yellowish white. You can see this on spectra; but you can also prove this easily by taking time exposures with a camera. If you use digital, it's vital you switch the "color balance" to "daylight" to stop the camera correcting for a color cast, because you want to know what color cast, if any, there is.

Here is the photo of the moon, almost due South of me.

The light isn't blue. Notice the white moon and the color of the clouds. There is also a hint of a "halo" from ice crystals - note that the trace of a rainbow in the cloud on the left of the moon has normal colors in it.
Here is a flash photo of the view from our garden (to prove it was very dark at 12:43 am) aimed at the moonlit hillside to the north.

Here is the same view, taken one minute earlier, on a tripod with no flash and a 20-second time exposure at f4.

The moonlight is just like sunlight! The house to the right is also partly lit by a street light - it's an orange colour because it's an incandescent lamp. The white spots in the sky are the stars.

Moonlight is very dim (about
0.5 - 1 lux). Here is my lux meter, caught with a flash photo whilst reading 1 lux from the moon.

Human colour vision almost fails at such low light levels; we use retinal cells called rods to see in dim light and we only see in black-and-white with these. Reptiles don't have rods; their vision is always in color and some nocturnal species can distinguish subtle hues of gray brown and blue in moonlight.

Thirdly, artificial "moonlight" and "infra-red" lamps are, compared to moonlight, intensely bright!
Here are some test result taken at 12 inches below the lamp using a lux meter:

Exo Terra Night Glo 50 W (Dark Blue) and Hobby Moonlight 40 W (Dark Blue) = 89 lux
Hobby Moonlight 75 W (Dark Blue) = 239 lux
ZooMed Nightlight 60 W (Red) = 349 lux
ZooMed InfraRed Heat 100 W (Red) = 4,880 Lux

Finally, we have this idea that moonlight does not affect animals. However, various research papers have reported that many nocturnal species behave differently on moonlit nights. Some small geckos increase their activity, whereas the activity of a larger species of gecko, and some rattlesnakes, was found to be much reduced if there was moonlight. And remember, we're talking about a maximum of 1 lux!

Even just opening the door of a darkened reptile room, allowing a chink of light from another room at the other end of the house to be seen, will provide more than 1 lux.

For humans, darkness enables the brain to synthesize melatonin, important in setting daily and seasonal body rhythms. If we are exposed to bright light in the middle of the night, melatonin synthesis stops dead in its tracks, and, ironically, blue wavelengths are by far the most effective for suppressing synthesis.

However, the situation in reptiles is different. The length of day and night and the depth of the night-time temperature drop are both important, and the effects of sudden light exposure are not the same as in mammals.
I'm not sure that a totally natural "day" and "night" are ever possible for a reptile kept in human habitation. But, I do think "night lights" can only make things far worse for the little guy in the cage.

To be continued to Part III---------------