Some Humidity and Temperature Effects under Reptile
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
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
In this second test, a different lamp was used. Starting point was
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
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
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.
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:
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
and very obvious difference. Here, we have overlaid an IR image over
a visible light image to illustrate this. The heating pattern is not
far more even, but (not shown here) also affects core temperature
much more rapidly than is seen where artificial sources are used.
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.
After just 30 minutes 'basking':
Some fresh mushrooms, carefully matched for size and weight:
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?
All text & images (c) Tortoise Trust 2014.