Why Lighting is Important to your Herp

The Facts

Ultraviolet light is defined as light that has a wavelength, measured in units known as nanometers, of 290-400. Humans cannot detect ultraviolet light (its wavelengths are shorter than those of visible light) but many other animals can.

The Ultraviolet Light emitted by the sun is divided into three types - Ultraviolet A (320-400 nm) Ultraviolet B (290-320 nm) and Ultraviolet C (100-290 nm). Almost 99% of the Ultraviolet Light that reaches the earth is in the form of Ultraviolet A.

Ultraviolet B Light

Exposure to Ultraviolet B light within the range of 290-310 nm is vital to the successful maintenance of heliothermic (sun-basking) reptiles in captivity. The action of UVB light on cholesterols within reptile skin results in the production of Vitamin D3. Vitamin D3 is needed to metabolize the calcium that reptiles obtain from their diets.

Except in very limited circumstances (see below) heliothermic reptiles cannot effectively utilize dietary Vitamin D3, but rather must manufacture it in the skin. Lacking Vitamin D3, they cannot utilize calcium for bone development and other necessary processes. Please see the article Metabolic Bone Disease for information concerning the problems that can arise when UVB light is not provided.

Ultraviolet A & C Light

The role of Ultraviolet A Light is less well-studied, but we do know that it plays an important role in promoting normal activity levels, mating behavior and immune system maintenance in many reptile species. For example, female Desert Iguanas (Dipsosaurus dorsalis) are unable to detect the secretions laid down by breeding males (and hence may fail to mate) unless UVA Light is present. Ultraviolet C light does not, as far as we know, play a significant role in reptile biology (but keep your eyes on the research!).

Which Reptiles Need UVB and UVA Exposure

The following reptiles should be provided with UVA and UVB light exposure in captivity:


All diurnal (day-active) species. Even those that dwell in canopied forests (i.e. many Chameleons) or below leaf litter (i.e. Glass Lizards) find ways to expose themselves to the sun’s rays.


All aquatic basking species, such as Painted Turtles, and all terrestrial species, such as Box Turtles and Tortoises. Highly aquatic turtles that rarely leave the water, such as Mata Matas, Snapping Turtles and Soft-shelled Turtles, seem to get along fine without UVA/B. However, as many seem to bask by floating at the water’s surface, I always provide them with a UVA/B lamp, just in case.


As far as is known, all commonly kept snakes obtain Vitamin D3 from their diets, and do not require an external UVB source. However, UVA is no doubt critical in maintaining normal behavior and possibly good health, and so should be provided. There is some evidence that Smooth and Keeled Green Snakes, and the various North American Water, Garter and Ribbon Snakes may require UVB light, so I suggest it as a safety measure.


All species (this provided for informational purposes only, I do not advocate the keeping of alligators or crocodiles as pets).

Ultraviolet Light & Amphibians

We know little of the role that ultraviolet light plays in the lives of amphibians. As many frogs and salamanders have a UVB “filter” of sorts in the skin, and incorporate UVB protectants into the eggs, it is believed that UVB light may be harmful to them. In fact, Wood Frogs and Gray Treefrogs kept under UVB-emitting bulbs often develop eye problems that seem, but have not been proven, to be related to UVB exposure.

If you keep amphibians in terrariums with live plants, be sure to provide them with a cave or other means of avoiding light exposure, and choose a low UVB output bulb such as the Exo Terra Repti Glo. I have successfully used this model with a number of frogs and salamanders.

Types of Lamps or Bulbs

We will never develop a lamp (please note, “light bulbs” are more properly termed “lamps”) that matches the light emitted by the sun. Whenever possible, provide your heliothermic reptiles with exposure to unfiltered sunlight - keeping in mind, of course, the very real danger of over-heating. Please remember that ordinary glass filters out beneficial ultraviolet light. Ultraviolet-permeable glass is available for those who wish to construct their own terrariums and cages, but it is quite costly.

That being said, we are fortunate in having available to us a wide range of lamps that allow us to keep reptile pets that require a source of UVA and UVB radiation.

Florescent Lamps

These elongated tubes were the first UVB-emitting lamps to be developed for use in the pet trade. The technology behind them improves each year, and models emitting varying strengths of UVB light are now available. Generally, florescent lamps are most effective when situated within 12 inches of the reptile, but be sure to check the manufacturer’s recommendations as this will likely change as new types are introduced. Florescent lamps emit very little heat.

Incandescent Lamps

Standard incandescent lamps provide heat but not UVB (but please see below – Mercury Vapor Lamps), and thus find their primary use in creating warm basking spots. However, they can be of indirect value in assuring that your pets receive ample UVA/B radiation - by positioning your incandescent lamp near the ultraviolet lamp, basking animals will be exposed to UVA/B as well.

Recently, UVB lamps that fit into incandescent fixtures have been developed.

Coralife's Reptile Spot Bright Light and similar models provide heat and UVA radiation, but not UVB.

Mercury Vapor Lamps

Mercury vapor lamps, such as Zoo Med’s Power Sun UV Mercury Vapor Bulb, are the latest innovation in the reptile lighting field, and hold great promise. They are especially valuable for desert-dwelling species that have especially high UVB needs, such as Dabb Lizards and Horned Lizards. Mercury vapor lamps broadcast UBV radiation over a much greater distance than do florescent lamps, and so are also ideal for use in large cages and exhibits, where animals might need to bask at distances greater than 12 inches from the lamp.

Furthermore, mercury vapor lamps are incandescent, and therefore produce heat as well as UVB light. Reptiles drawn to the lamp’s heat will be exposed to maximum UVB levels while basking, and the need for a second heat-producing lamp is eliminated.

Be sure to read the manufacturer’s recommendations regarding basking distance and heat output carefully, and use mercury vapor lamps only in ceramic fixtures (unless otherwise instructed by the manufacturer).

UVB Meters

UVB meters are a valuable tool for serious herptoculturists. These allow you to quickly monitor your lamp’s output at various distances, so that you can arrange a basking site that will assure maximum UVB exposure for your pet.

Please note also that UVB output declines over time, despite the fact that the lamp remains brightly lit. By using a UVB meter, you can detect this decline and perhaps move the basking site closer to the lamp. Alternatively, you can replace the UVB lamp and move the used one to a terrarium where it can be brought closer to another of your pets, or you can save it for emergency use. In this way you will obtain the maximum lifespan possible from your UVB lamps.

The Role of Diet

Although heliothermic reptiles require UVB radiation in order to synthesis Vitamin D3, they should never-the-less be provided with dietary Vitamin D3 as well. This is best accomplished by feeding them a varied diet and a high quality vitamin supplement. This is especially true in light of anecdotal evidence which suggests that in certain circumstances, heliothermic reptiles may be able to make use of Vitamin D3 consumed with food - please see my blog Has Anyone Seen This… for information concerning a population of Standing’s and Madagascar Giant Day Geckos that are faring well in the absence of UVB radiation.

Author: Frank Indiviglio