Some Humidity and Temperature Effects under Reptile Basking Lamps

These graphs illustrate the dramatic reduction in ambient humidity experienced directly beneath various common reptile basking lamps. In all cases
humidity is reduced very rapidly after the lamp is turned on. Typical room ambient humidity levels were employed as a starting position. The general
room ambient was also monitored simultaneously at a distance of 2M using an independent data logger.

In this first graph ambient room humidity level was 70%. Within seconds, under the basking lamp the levels fell to 30%, then to below 20%.

The lamp was switched off and levels recovered.

It was then turned on again and levels fell as before.  Levels of 20% and below are extremely damaging if sustained, even for arid habitat species.

Humidity 1

In this second test, a different lamp was used. Starting point was circa 43%RH.

Lamp Humidity 2

The glass envelope size, power, distance from target and spectrum of the lamp all affect the precise results, but in every case tested to date all lamps
without exception have produced dramatic reductions in the relative humidity present in the basking zone. In worst case examples, RH has been observed to
fall as low as 14%. This is acutely dehydrating to any living organism. In general, RH (even for semi-arid habitat species) should be maintained between 45-60%
for most of the time. In wild, animals will experience lower, but they normally do so for relatively brief periods before retreating back to more temperate microclimates.
Sustained levels <20% RH will result in severe, and rapid, fluid loss in many species. Chronic dehydration is a serious problem in captive reptiles and is associated with
renal disease, the formation of uric acid bladder 'stones' and in gout - all of which are frequently reported in the veterinary literature and which are particularly common in tortoises
and larger lizards.

Simply raising the starting (ambient) is not sufficient, as the fall experienced beneath the lamps is so severe. Also, if the starting, background humidity is raised high enough to produce normal, safe levels
in the basking zone, tests have shown it has to be at near saturation point, and in a closed or semi-closed environment. Unfortunately, this creates additional problems, including some with quite seriously
negative implications for health. Such high levels are ideal for the growth of many pathogens (fungal, bacterial and viral) and sustained levels of very high ambient humidity can also have very severe
effects upon reptile keratin - causing softening, deterioration, and a substantially increased risk of infection.

It is speculated that the generation of non-waterfiltered IR-A is at least to some extent implicated in these results.

A further effect under these lamps is of an unbalanced 'hot spot', where part of the body either overheats or achieves correct basking temperatures, while other parts remain too cool.

Hotspot 1

There is also some evidence that again, the IR-A spectrum generated by many lamps could be having a direct effect upon subcutaneous fluids in exposed areas:

Hotspot 4

The degree to which this may be implicated in the high incidence of thermal burns seen in captive reptiles is under investigation.

If we compare the patterns of heating under these lamps with that seen in tortoises basking under natural conditions there is a very significant
and very obvious difference. Here, we have overlaid an IR image over a visible light image to illustrate this. The heating pattern is not only
far more even, but (not shown here) also affects core temperature much more rapidly than is seen where artificial sources are used.

Image Blend

Finally, this is certainly not purporting to be a conclusive scientific result, but I was tempted to see what happened to various non-animal objects placed beneath
some 'reptile basking lamps' purchased from pet stores.

First, a piece of wood - with moisture content meter.


Wood 2

After just 30 minutes 'basking':

Wood 1

Some fresh mushrooms, carefully matched for size and weight:

Fresh Mushrooms

In this case, a slightly more controlled test was carried out. One mushroom was exposed to natural sunlight for 8 hours on a roof terrace here in
Southern Spain. The second was placed in the same area, but was shielded from the sun, and instead exposed to a 100w basking lamp. The height of this was
adjusted regularly so that the surface temperatures of the two mushrooms matched closely. The airflow and ambient humidity was absolutely identical throughout
the test. Neither mushroom exceeded 20C. This is the result after 8 hours. The mushroom on the left is the one from under the lamp. The mushroom on the right lost 17%
of its starting mass. The mushroom on the left lost 44%.

This raises several interesting questions, just one of which is that if this is what happens to a block of wood or mushroom, what might be happening to a juvenile lizard or tortoise?

Dehydrated Mushrooms

All text & images (c) Tortoise Trust 2014.