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Rethinking Reptile

Reptile and amphibian lighting from a natural-history perspective.

by Shane Bagnall

www.reptilechannel.com | 3

While some geckos

to

w

are diurnal, like this
Madagascar giant day
gecko, many nocturnal
geckos become active at
dusk and receive low levels
of UVB before the sun sets.

n the early 1940s, our knowledge of the
effects of light on reptiles and amphibians
was very limited. It wasn’t until 1944
that we learned of the amazing ability of
reptiles to maintain relatively stable body
temperatures through thermoregulation.

This was the result of a groundbreaking
study by herpetologists Raymond Cowles and
Charles Bogert, who coined the terms “ectotherm”
and “endotherm.” Their landmark study inspired
numerous research projects on the effects of light
and heat on reptiles.
Since then, our knowledge of reptile
lighting has increased tremendously. We now
know that many reptiles and amphibians can see
things illuminated by ultraviolet-A, and that they
can make vitamin D in their skin upon exposure

to ultraviolet-B. When housed in captivity

without access to UVB, many reptiles

developed a form of metabolic

bone disease (MBD) that

results in soft, deformed

Courtesy Kirby Spencer / Zoo Med Laboratories

2 | Reptiles

Rep

bones and is often fatal
if not corrected by UVB
exposure. With this
knowledge came the
introduction of the
fi rst commercially
available UVB
lamp for reptiles
in 1993, which
allowed people
to successfully
maintain and
breed a variety of
reptile species in
captivity. Although
preventing the onset
of disease is good
motivation to provide
adequate lighting for
captive reptiles, many
keepers are going to
the next level in an effort
to accurately recreate truly
naturalistic habitats, even with
respect to lighting.
Humans see the world differently
than reptiles and amphibians. Many reptiles and
amphibians have the remarkable ability to see
things illuminated by UV wavelengths. Also, some
lizards and amphibians have a third eye on the top
of their head known as the parietal eye. This eye
cannot see the full complement of colors that the
other two eyes see, but it can sense light and is
associated with photoperiod regulation (circadian
rhythms), reproductive behavior, basking behavior
and thermoregulation. The parietal eye may also
be sensitive to UV wavelengths (Jenison, 1980).
These differences in how reptiles and humans see
have caused persistent confusion on what defi nes
full-spectrum lighting and UV lighting.

Full-Spectrum and UV Lighting

The term “light” is typically associated
with vision, and because people are the ones
doing the research, we have identifi ed the
visual portion of the electromagnetic spectrum
according to the colors that we are able to see.
Full-spectrum lighting for reptiles should have
emissions in the human visible wavelengths (red

Panther chameleons have been the

subject of much UVB research over

the years. This hatchling was bred at

Zoo Med and receives UVB from an

energy-effi cient, compact fl uorescent

UVB lamp.

Courtesy Kirby Spencer / Zoo Med Laboratories

Photoherpetology

Many think of the word “photo”

eferring to a picture, but

as r
the original meaning of the
word is “light.” “Photograph”
literally means “drawing with
light.” The study of the effects
of light, or photons, on living
things is called photobiology.
Herpetology is defi ned as
the study of reptiles and
amphibians. By combining
these two terms, I propose a
new word to give identity to the
growing fi eld of the study of
reptile and amphibian lighting:
photoherpetology.

Reptiles | 3

tiles | 3

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Rep

This electromagnetic
spectrum shows the
difference between the
vision of humans and
the vision of reptiles and
amphibians.

Courtesy Shane Bagnall

through violet), in
addition to emissions
in the UVA region of
the electromagnetic
spectrum. It is
important to note
that a full-spectrum
reptile lamp may not
produce UVB, unless
the manufacturer
specifi cally states so on
the package.
The shorter
wavelengths adjacent
to the human visible
wavelengths of the
electromagnetic

spectrum are
appropriately called ultraviolet. These wavelengths
are broken into three categories: UVA, UVB
and UVC. As mentioned, many reptiles and
amphibians can see things illuminated by UVA
light, and thus UVA makes up a portion of their
visible spectrum. UVB wavelengths are shorter
than UVA wavelengths and may or may not be
visible. Even though lamps are used to produce
UVB, the term “UVB light” is a bit of a misnomer,
because animals may not have the ability to see
things illuminated by UVB wavelengths. UVB
is associated with synthesis of vitamin D in the
skin, in addition to playing a role in the immune
system of animals. There is evidence that reptiles
can sense UVB and will adjust their exposure
based on the amount of vitamin D in their blood.
UVC and shortwave UVB wavelengths below
290 nanometers do not penetrate the earth’s
atmosphere and are harmful to animals.

4 | Reptiles

UVB, Vitamin D and Calcium

The process of vitamin D synthesis in
the skin of animals upon exposure to UVB is
fascinating. Cholesterols in the skin are converted
to a molecule known as previtamin D3 when the
skin is exposed to UVB radiation. Upon exposure
to heat, previtamin D3 undergoes a change and
is converted to vitamin D3, which transforms in
the liver and kidneys to the active form of vitamin
D3. There are other molecules involved, and the
process is regulated so that excess UVB exposure
will not lead to an overdose of vitamin D, which is

tiles

fat soluble and carries a risk of overdose, as do all
fat-soluble vitamins.
In addition to being a major component
of bones and eggshells, calcium is involved in
countless biological processes at the cellular
level, including cell communication, muscle
contractions and other functions that are
essential to life. Vitamin D3 is responsible for
calcium metabolism, and if there is not enough
circulating vitamin D3 in the blood, animals
are not able to use the calcium in their gut
that they get from their food. Dietary calcium
would then pass through the gut unused, and
animals would be forced to take it from their
bones, ultimately leading to a form of metabolic
bone disease known as nutritional secondary
hyperparathyroidism.
Animals can get vitamin D from two
different sources: UVB-induced synthesis in
the skin, or by ingesting vitamin D in the food
that they eat. The livers
of vertebrate prey, for
instance, such as mice,
rats and cod, provide a
rich source of vitamin
D3. Researchers have
found, however, that
not all reptiles and
amphibians are able to
adequately use dietary
vitamin D3, and they
depend on UVB-induced
synthesis of vitamin
D in the skin. Some of
the reptiles for which
this has been shown
to be the case include

Fluorescent lamps that

provide UVB, UVA and

human-visible light.

Courtesy Shane Bagnall

Seen here is a Gooch

& Housego model

OL-756 scanning double-

grating monochromator

spectroradiometer (left)

alongside a Solartech

model 6.2 UV-B Solarmeter

digital ultraviolet

radiometer (right). Both

are used to measure light.

Courtesy John C. Dowdy

Reptiles | 5

til

hibi

se

Self-ballasted mercury
vapor lamps provide UVB,
UVA, human-visible light
and heat from one source.

Courtesy Shane Bagnall

Without UVB, this bearded

Without UVB, this bearded

dragon would be at risk of

dragon would be at risk of

developing metabolic bone

eveloping metabolic bone

disease.

i

strictly herbivorous species, along with some
insectivorous and omnivorous species (and the
list is growing).
While some reptile species, such as the
bearded dragon, could likely not survive without
UVB-induced synthesis of vitamin D, others
seem to do fi ne with what they get from their
diet. Snakes are commonly kept by breeders in
utilitarian enclosures containing a water dish,
bedding, a hidebox and subterranean heat to
provide a thermal gradient. These enclosures
are often less than 6 inches tall, and the snakes
are not provided with any lighting except for the
ambient room lighting that may pass through
the walls of the enclosure. Does this mean that
snakes don’t benefi t from UVB? While this type
of enclosure may be similar to what the snakes
experience in a burrow, eventually they have
to come out, and when they do they are often
exposed to some level of UVB.

A Natural History Approach to Reptile and
Amphibian Lighting

Often, we base husbandry practices on

common sense and what has proven to work in
the past, and many keepers provide specialized
lighting only for species that need it to survive.
Success in keeping reptiles and amphibians is

uccess in keeping rep

often defi ned as being able to raise

often defi ned as being able to raise
animals in captivity that appear

animals in captivity that appear
healthy, and that hopefully

ealthy, and that hopefully

breed and produce healthy

reed and produce healthy

offspring. Based on this

offspring. Based on this
success, the conclusion is

uccess, the conclusion is

drawn that if they can

drawn that if they can
grow and reproduce

row and reproduce

without access

ithout access

to UVB,

o UVB,

es and amp

ans is

Courtesy Kirby Spencer / Zoo Med Laboratories

6 | Reptiles

they must not need it. But this logic completely
ignores the fact that many of these reptiles are
exposed to UVB in their natural habitat, and new
research shows that they do indeed benefi t from
UVB exposure.
Some species have been kept with
apparent success without access to
UVB, including nocturnal lizards;
reptiles, such as snakes and
varanids, that eat whole
vertebrate prey; and
amphibians. If we were to
take a different approach
and choose their
lighting based on their
interaction with light
in nature, however, we
would provide most of
these species with UVB.
Many of the species
that are classifi ed as
“nocturnal” are also
crepuscular (active at
dawn and/or dusk), and
crepuscular behavior
patterns often result in
exposure to low levels of
sunlight and UVB.

These juvenile

curly tailed lizards

were bred at Zoo Med and

are housed in a terrarium

with a mercury vapor UVB

lamp, which provides heat,

light, UVA and

UVB from one source.

Courtesy Kirby Spencer /Zoo Med Laboratories

UVB for Nocturnal Species

Herpetologists have often
come across nocturnal species at dusk
when low levels of UVB are present. In “Diurnal
Activities of a Nocturnal Animal,” a 1952 article
published in the journal Herpetologica, noted
herpetologist Bayard Brattstrom makes the
following remarkable statement:

“The increasing mass of evidence regarding the
function of the pituitary gland of animals in relation
to solar radiation and sexual and other associated
cycles, and the known importance of vitamin D
and other physiological factors associated with
absorption of solar radiation, would seem to make
desirable the report of instances of diurnal activity
observed in supposedly nocturnal animals. This
is especially true for the species of terrestrial
animals that habitually live underground during
daylight hours, and which by means of protrusion
of the head alone could presumably receive

Reptiles | 7

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p

Rep

s

The author’s gopher snake
habitat contains UVB
lighting, an undertank
heater and a shelter to
allow for photoregulation.
This snake moves
throughout the entire
habitat and often exposes
himself to UVB.

Courtesy Shane Bagnall

adequate dosages of light suffi cient to induce such
responses as reported for birds and mammals.”

In this article, Brattstrom describes the
observation of a desert banded gecko (Coleonyx
variegatus variegatus) during the late afternoon
when the sun was still above the horizon. I, too,
have observed this species active during the late
afternoon in Phoenix.
The important message is that nocturnal
species occasionally expose themselves to UVB
on purpose, and that this limited exposure to
UVB may be enough to support a healthy vitamin
D condition. Nearly 50 years after Brattstrom’s
observation, a study on house geckos revealed
that this nocturnal/crepuscular species is
extremely effective at synthesizing vitamin D with
very little UVB exposure (Carman et al., 2000).

Based on these fi ndings, it seems that
for nocturnal and crepuscular species of reptiles,
it is logical to recommend the use of lamps that
provide low levels of UVB comparable to the
levels found at dusk. In addition to providing a
proper photoperiod, the lamps can also provide
necessary UVB for vitamin D synthesis. Even if
they only expose themselves to the light for short
periods of time, that doesn’t mean that animals
don’t benefi t from the light. We use a toothbrush
for only a few minutes each day, but imagine
living without one!

What About Snakes
and Amphibians?

With amphibians, UVB has often been the

subject of controversy as it has been implicated

8 | Reptiles

tile

as a potential cause of amphibian decline. Indeed,

Rep

too much UVB is harmful to any animal, and
different species have differing tolerances for
safe UVB exposure. As amphibians have become
the focus of intensive captive-breeding projects,
many zoos and breeders have found that low
levels of UVB are necessary in order to maintain
and breed various species. Breeders of dart frogs
regularly use UVB lamps, and breeding projects
involving the endangered Panamanian golden
frog (Atelopus zeteki) also employ the use of UVB
lamps with great success.
Even though many snakes can be raised
and bred in captivity without the aid of UVB,
the fact remains that most snakes receive UVB
exposure in nature. There are many reports of
snake activity when the sun is still out for species
that are considered nocturnal. Some snakes,
including rattlesnakes, racers, gopher and bull
snakes, and garter snakes, are strongly diurnal
and expose themselves to strong levels of UVB.
Previously, the majority of the UVB studies on
reptiles dealt mainly with lizards, but a recent
study on corn snakes (Elaphe guttata) revealed
that they, too, appear to have the ability to
synthesize vitamin D upon exposure to UVB
(Acierno et al., 2008).

As discussed earlier, UVA and UVB are
also important in vision, behavior, reproduction
and immune response. Due to the abundance
of snakes bred in captivity, and their popularity
as pets, they would seem to be an important
group for future studies involving UVB and UVA
radiation in the fi eld of photoherpetology.

Aquatic turtles should be
provided with UVB and a

heat source to promote

vitamin D3 synthesis and

calcium metabolism.

Courtesy Kirby Spencer / Zoo

Med Laboratories

Reptiles | 9

tiles | 9

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References

In Closing

Acierno, M.J, M.A. Mitchell, T.T.

Zachariah, M.K. Roundtree, M.S.

Kirchgessner and D. Sanchez-

Migallon Guzman. 2008. “Effects

of ultraviolet radiation on

plasma 25-hydroxyvitamin D3

concentrations in corn snakes

(Elaphe guttata).” American

Journal of Veterinary Research,

69(2):294-297.

Brattstrom, B.H. 1952. “Diurnal

Activities of a Nocturnal Animal.”

Herpetologica, 8(3):61-63.

Carman, E.N., G.W. Ferguson, W.H.

Gehrmann, T.C. Chen and M.F.

Holick. 2000. “Photobiosynthetic

Opportunity and Ability for UV-B

Generated Vitamin D Synthesis

in Free-Living House Geckos

(Hemidactylus Turcicus) and

Texas Spiny Lizards (Sceloporus

Olivaceous).” Copeia, 2000(1):245-

250.

Cowles, R.M. and C.M. Bogert.

1944. “A preliminary study of the
thermal requirements of desert

reptiles.” Bulletin of the American

Museum of Natural History,

86:261-296.

Jenison, G. and J. Nolte. 1980. “An

ultraviolet-sensitive mechanism

in the reptilian parietal eye.” Brain

Research, 194:506-510.

As our knowledge of the UVB and

lighting requirements of reptiles and amphibians
grows, so will our ability to provide for their
needs in captivity. When positioning UVB lamps
over terrariums, be sure to follow manufacturer
recommendations for appropriate lamp distances,
and observe the behavior patterns of your reptile
or amphibian. Take notice of unusual behaviors
that may indicate that the lamp is too close
or too far. Continual avoidance of the light for
species that commonly bask is a good indication
that the lamp is too close or too strong for that
particular application. On the other hand, if an
animal continually basks and exposes itself to
UVB, without occasionally retreating to perform
other natural behaviors, this may be an indication
that the lamp is too far or that a stronger UVB
lamp may be desirable. Care should be taken
to ensure that a UVB gradient is provided and
that the reptile or amphibian can retreat to a
shelter where no UVB is present. This will allow
them to photoregulate and adjust their exposure
to UVB, just as they do with heat through
thermoregulation.
The next time you set up a new habitat
for a reptile or amphibian, take some time to
research the natural history and behavior patterns
of that species. Not only will this information prove
to be interesting, it will also aid in helping you
make an educated choice on the proper lighting
requirements from a natural history perspective.

I would like to thank Dr. John C. Dowdy (Rapid Precision
Testing Laboratories), Dr. Gary Ferguson (Texas Christian
University) and Andy Quinn (Zoo Med Laboratories) for
reviewing this article and providing valuable comments. I

Learn About

UV Lamp Measurement Tools

To read about the tools used

for measuring UV lamps, visit

ReptileChannel.com/MeasureUV.

would also like to thank Gary Bagnall for inspiring

my interest in herps at an early age.

Shane Bagnall studied herpetology at San Diego State

University, where he received his degree in biology with
an emphasis in zoology. Following his time at SDSU, he
studied machining and manufacturing, which led him
to the prestigious Salk Institute, where he designed
and built custom scientifi c instruments. Shane is now a
member of Zoo Med’s research and development team,
and he spends much of his free time studying the local
herpetofauna of California’s central coast. Visit Zoo Med
at zoomed.com.

10 | Reptiles

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For more information, call 1-800-PET BOOK

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