February 22, 2019

Crested Geckos and UVB – Oh My!

Increased appetite, growth, activity, lifespan due to natural vitamin D3
Done improperly could harm the animal’s eyes & skin, shorten lifespan

Crested geckos are known to survive both with and without UVB in captivity. Since we cannot ask the animal, the critical argument is whether a life without UVB is detrimental. Part of the reason this is such a hot debate is that the herping community has not had as many years to study captive crested geckos as other reptiles, due to the fact they only really entered the pet trade in the early 90s.

“Few studies have yet been done on vitamin D3 synthesis in nocturnal and crepuscular reptiles…”


In that short amount of time, it can be difficult to know the effects of improper care – or what constitutes improper care to begin with! Vitamin D3 is a key to sustaining life. Some say that without UVB a reptile is not able to process properly from the digestive system. So dusting those insects could be mostly useless on one end of the scale, and harmful on the other extreme.

“During exposure to sunlight 7-dehydrocholesterol in the skin absorbs UV B radiation and is converted to previtamin D3 which in turn isomerizes into vitamin D3. Previtamin D3 and vitamin D3 also absorb UV B radiation and are converted into a variety of photoproducts some of which have unique biologic properties. “


“Many species can absorb vitamin D3 when it is given as a supplement with food, but this is hardly a natural process! It seems likely that the natural way these reptiles obtain their vitamin D3 is from synthesis in their skin when it is exposed to UVB during daylight hours.”


Many people who use UVB with their cresteds have noted better feeding habits, growth, activity, and lifespan. But is that a correlation or a causation?

Correlation is a statistical measure (expressed as a number) that describes the size and direction of a relationship between two or more variables. A correlation between variables, however, does not automatically mean that the change in one variable is the cause of the change in the values of the other variable. Causation indicates that one event is the result of the occurrence of the other event; i.e. there is a causal relationship between the two events. This is also referred to as cause and effect.


Without actual scientific study – the increased appetite and lifespan, etc could be due to better overall husbandry. The type of people choosing to use UVB in the first place might be more informed in other areas and potentially provide better habitats and care.

You might ask – ok, so if UVB is proven to help reptiles, why is this still such a hot debate?

Crested gecko eyes are proportionally larger than most reptiles, the pupil can expand to gather light in dim environments. They are known to be more active at night (nocturnal) and in the low-light dawn and dusk hours (crepuscular). They also, obviously, have no eyelids.

“…lizards follow a consistent pattern of eye-shape variation with activity pattern, as predicted by the principles of dioptrics: nocturnal species consistently exhibit a larger relative corneal diameter than do diurnal species, probably as an adaptation for increased visual sensitivity…”


Habitat plays a large role – crested geckos in the wild spend most if their time in moist, shady areas during the day and foraging in the low-light hours. Also, the sun isn’t out all day – clouds pass by, rainstorms, etc. There are natural periods of light and shade in the wild environment.

The Ferguson Zone for crested geckos is the lowest on the scale: shade method gradient UVI 0-0.7. That means if you place a 10.0 sun-loving desert species bulb on your little 12x12x18 Exo Terra enclosure – you can over-irradiate your little friend’s eyes and skin.

“A gradient is vital; there must be a full range of UV levels from zero (full shade) to the maximum suggested by the Zone assessment (at the closest point possible between the reptile and the lamp).”


There are numerous reports of photo-kerato-conjunctivitis in reptiles with eyelids such as iguanas, skinks, and bearded dragons. Crested geckos do not even have the ability to self-shield their eyes so they are especially vulnerable. While natural sun is far stronger than bulbs, UVB can be overdone.

A crested gecko is stuck in a small box with eyes suited for low-light levels and no eyelids; common sense should prevail that UVB could (and does) easily harm this little creature when no proper shade is offered, a overly high output bulb is used, or the enclosure is too small to escape the radiation. The wild is a variable place, and while some argue the sun is always present so it should be in captivity – remember your gecko’s world is limited by the size of the enclosure. UVB benefits the animal, and the responsibility falls on the keeper not to be lazy. UVB is not a one and done bulb on top of the enclosure.

“…we need to ensure that our vivariums allow their inhabitants the freedom to self-regulate their exposure to heat, light and UV within the range that is appropriate for the species. In the wild, sunlight interacts with features such as trees, rocks, plants and water, creating superimposed gradients of heat, light and UV extending from full sunlight into full shade.”


In Conclusion
UVB can be used to a crested gecko’s benefit as with most reptiles, but only if done in an intelligent manner. Too much of a good thing is bad. Remember these animals are stuck in a box, it is our responsibility to provide quality care.

  • UVB output measuring devices are a wonderful tool to measure bulb effectiveness and strength. Without it everything is guesswork.
  • Enclosures should be large enough for the animal to escape the UVB in shaded areas, as well as thermoregulate.
  • It is easy to provide too much UVB for animals in the lowest Ferguson Zone.
  • A timer can help mimic natural photoperiods of sunshine and shade from clouds and rainstorms.

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R1: Reptiles UVB, Ferguson Zone – http://www.reptilesmagazine.com/An-In-Depth-Look-At-UV-Light-And-Its-Proper-Use-With-Reptiles/
R2: Selecting UV in reptiles – https://www.jzar.org/jzar/article/view/150
R3: UV lighting for reptiles – http://www.uvguide.co.uk/vitdpathway.htm
R4: Reptiles UVB & Skin – http://www.uvguide.co.uk/skintests.htm
R5: Vitamin D3 Use/Absorption  & Humans – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3897598/
R6: UVB Damage & eye Issues – http://www.uvguide.co.uk/phototherapyphosphor.htm
R7: Eye shape studies – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3497252
R8: Statistical Language – Correlation and Causation https://www.abs.gov.au/websitedbs/a3121120.nsf/home/statistical+language+-+correlation+and+causation

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