in Reptile Lighting
resource for all reptile keepers
Light in the Vivarium
Benefits and the Risks
reptiles really need UVB at all, with vitamin D in their
vitamin D or Ultraviolet Light? - A controversial issue.
It has long been known that some species of reptiles which
do not normally bask in sunlight- including most
nocturnal or crepuscular lizards - may be kept and
bred successfully in captivity with no access to ultraviolet
light, provided that adequate levels of vitamin D3 are provided
in the diet. These are mainly carnivorous or insectivorous
species which might be expected, in nature, to obtain a
considerable proportion of their vitamin D3 from their diet.
Most of the literature on the husbandry of these species
states that UVB is unnecessary.
Diurnal lizards of quite a
few species have also been kept and bred successfully by
zoos and private keepers supplying them with dietary D3
supplementation but no ultraviolet light.17,39
This would appear to be an abnormal
situation for these reptiles since, in the wild,
many of these species do bask in sunlight, and would almost
certainly utilise ultraviolet light to synthesise much of
their vitamin D3. Much skill and considerable experience
is needed to ascertain the correct level of supplementation.20
Failure to provide adequate D3 results in metabolic bone
disorder, and this condition has been seen frequently in
captivity. Oversupplementation causes equally disastrous
hypervitaminosis-D. This is presumably because the body
has not evolved any efficient way of dealing with dietary
excess, since natural foodstuffs are very unlikely to contain
toxic levels of vitamin D.5,22
Certain species, however, do not seem able to utilise
vitamin D3 effectively from their diet. This may be because
in the wild, their diets are particularly low in vitamin
D3 and they are adapted to rely almost entirely upon UVB
photobiosynthesis for this vitamin.
Vegetarian lizards might be expected to fall into
this category, since plants contain predominantly vitamin
D2, which is not thought to be utilised by reptiles.8
However, insectivores and even carnivores may fall into
this category. Not only green iguanas
but also giant day geckos
and Komodo dragons fed experimental
diets containing vitamin D3 and calcium, but deprived of
UVB light, have developed pathological symptoms.1,7,8,20
exposure of reptiles to UVA
provides known physical and psychological benefits.
It is possible that UVB also
provides psychological benefits; and reptiles have a natural
ability, as we have seen, to use UVB light to create exactly
the required amount of vitamin D3.
Most reptile keepers therefore
choose to supply ultraviolet light to all diurnal lizards
that are known to bask in sunlight in the wild, rather than
deprive them of its benefits and experiment with dietary
light to reptiles in captivity.
best and most balanced source of ultraviolet light is, naturally,
the sun. Where reptiles are kept in climates where it is
feasible to allow them access to natural, unfiltered sunlight,
this is often the ideal option, provided the animals have
free access to shade and shelter, as they would in the wild,
and the environmental temperatures are suitable for them.
Outdoor enclosures are used to great effect in many zoos
and private collections.
However, many tropical species need indoor housing, in temperate
climates, for much of the year. Over the last decade, increasingly
sophisticated light sources have become available to the
hobbyist needing to supply captive reptiles with a source
of UVB indoors. Today, in the UK there are several brands
of fluorescent tubes and compact lamps available in a range
of shapes and sizes, and mercury vapour bulbs designed to
produce even higher levels of UVB.
Dangers of Overexposure to Ultraviolet Light.
The benefits of moderate exposure to natural sunlight
are undeniable, both for humans and for many species of
However, it is also well known that in mammals at least,
excessive exposure to the sun's ultraviolet rays
- or their artificially produced equivalent - can be harmful. The situation in reptiles has not, apparently, been studied in detail, but is almost certain to be similar.
as our test results show, the UV output from many lamps
sold for reptile use is only a fraction of that found in
natural sunshine, all artificial sources of UV radiation
must be treated with respect. Moreover, some of the latest
mercury vapour lamps do emit high UV at close range. Manufacturers'
recommended minimum distances should always be taken seriously.
UV radiation has a damaging effect upon living cells.13,45
In mammals both the skin and the eyes may be injured and
there are both immediate and long-term effects.
cells may be killed outright (as in "sunburn"), but surviving
cells may suffer damage to their nucleic acids (DNA and RNA)
which can predispose to certain types of cancer
and also suppress the immune system.
is believed that reptile skin, being generally much thicker
and often more heavily pigmented than mammalian skin, may
be more resistant to the detrimental effects of UV light.
However, cases of possible "sunburn" have been described;
some of these may actually be thermal
burns from hot UVB-emitting lamps.33
exposure to UV lamps is also reported as causing a
toxic syndrome and hyperkeratosis
(a pathological skin thickening) in side-blotched lizards
(Uta stansburiana), lethargy,
skin darkening, anorexia and death in iguanas, and
egg hatching failure and
skin tumours in panther chameleons.1
Damage to the eyes is well documented in mammals.
Immediate effects include photokeratoconjunctivitis (snow
blindness, "welder's eye") and long-term effects include
certain types of cataracts (opacity of the lens). Although
there does not appear to be published literature on either
of these conditions in reptiles, several reptile keepers
have recently described symptoms of
photokeratoconjunctivitis in lizards kept in close
proximity to new high-UVB output lamps of several types.
Typically, the lizard's eyelids swell up and close, and
it becomes depressed and lethargic. The condition clears
rapidly when the lamp is removed or exchanged for an older
one or different type.4
The formation of cataracts
has been described in snake eyes following the snake's forced
exposure to bright light. However, in some cases the artificial
light thought to be responsible was not emitting UVB.10
Reptile eyes do have some differences in their ocular structure
and in the composition of the lens and aqueous humour. These
differences may afford some protection from UV light.1
In the absence of more information, we need to ensure as far
as possible that our reptiles are not exposed to levels of
UVB which would be un-naturally high for a wild animal of
that species in its normal habitat. In addition, a reptile
should always be able to move out of the effective range of
its UVB light. "Extra" UVB above the requirement for D3 production
is of no benefit, since as we have seen, the photo-biosynthesis
is a self-limiting process; when sufficient is made, additional
ultraviolet light merely breaks down any excess formed.
© 2005 UVGuide.co.uk