How to Light a Herptile's Cage


One of the most enduring sources of confusion in the herptile hobby is the issue of lighting a cage. I find myself disentangling people’s notions and assumptions on a daily basis: What is the proper lighting for my animal? Does it even need a special light? How do I heat AND light a cage? Where do I put the light? How long does it stay on?


The questions seem to be endless.


Let’s start at the beginning: Lighting and heating are different issues. They often require separate solutions, and attempts to solve both issues with one light are usually fruitless. 


Often, a customer walks up to the counter and asks, "What light do I need for my pet?" Yes—the question is often that vague. My answer is, "Well, what’s the pet?" Some species require rigorous lighting while others require none at all.


Once I have established the specific species we’re talking about, I ask about the current caging. It is remarkably common that the customer has an entirely inappropriate setup and we have to work backward from that. Once we have the cage (and heating) right, we can now worry about light.


When we are talking about light, we are generally referring to bulbs that produce UVB. To my great consternation, many companies make heat bulbs and mark the package with the claim that they provide UVA. That’s true, but it is mighty confusing to customers who think that on its own is sufficient for herptiles.


UVB is the light that animals use to internally produce vitamin D3, a necessary component in the ability to absorb calcium. Without D3, calcium simply passes right through the animal. Equally important is the fact that UVB is the spectrum of light that reptiles see. An animal that sees its surroundings clearly will act more naturally, eat more readily and generally be more alert and active. This light source is essential for diurnal animals, tropical and desert species, and basking animals—including many nocturnal species that sleep in the sun.


Many of the UVB bulbs on the market are designed for an incandescent, screw-in fixture. These are perfectly fine for tall cages with a small footprint, such as arboreal cages for vine snakes, baby chameleons or crested geckos, but for larger cages and cages that are more long than tall, these bulbs will not work.


Think of it like this: You are in a windowless room, and the only light coming in is through a 6 in. hole in the ceiling. Is that small beam of sunlight sufficiently lighting the room? Of course not.


Similarly, in a long—or deep—cage, having a UVB light that effectively hits one small portion of the cage is, well, silly. A fluorescent bulb that extends the length of the cage is absolutely required.


There are also incandescent bulbs that produce both UVB and heat. While they work as advertised, you still have the problem of providing UVB only at the small portion of the cage where the animal might bask. To my way of thinking, this is not doing the trick. Not only that, but these bulbs are remarkably expensive yet seem to burn out at the same rate as ordinary heat bulbs. Whereas UVB bulbs need to be replaced on a yearly basis (the UVB deteriorates long before the bulb appears to need replacing), the customer might be replacing these bulbs every six months!


Most UVB bulbs come in two strengths: 5.0 and 10.0. In a general sense, I recommend the 5.0 bulbs for temperate and subtropical species. Examples might be water turtles, like red-eared sliders, arboreal geckos and even some frogs. The 10.0 is designed for tropical and desert dwellers: bearded dragons, iguanas, uromastyx, and desert and scrub tortoises. If you are confronted with an animal for which you have no experience, don’t guess. Do some research!


There are also two bulb widths on the market: the T-8 and the thinner T-5. The T-8s are for those who have generic fixtures that carry that size, and they work well. But the T-5s seem to be the wave of the future. As I understand it, they are more energy efficient, and who can argue with that? But I invite you to run an experiment: Set up two cages next to each other, one with a standard T-8 fixture and one with a T-5. We will assume that both produce UVB light (invisible to us) in equal proportions. But look at the *quality* of the visible light.


The T-5 is hands down a prettier, brighter and more vibrant light. So, if my customers already have a fixture, I sell them the T-8 bulb. But I also tell them that when that fixture inevitably fails (as all things electric do), they need to move on to the T-5. For customers who are doing a new setup, I steer them to the T-5. Zoo Med makes an excellently designed line of T-5 fixtures. They sit nice and compact atop a glass tank or can be mounted using L brackets inside a wooden cage.


Speaking of glass, one word of caution: Glass wipes out any UVB rays you are projecting into a cage. Putting a UV light on an "aquarium" top is absolutely pointless! By the same token (and this relates to heat), glass amplifies infrared light, turning a glass tank into a small oven. If your customers tell you that their pets get plenty of natural sunlight because their cages are in the window, gently tell them that inevitably, they will, one fine and warm sunny day, have barbecued pets, who coincidentally got 0 percent of their UVB requirements.


Some people will also tell you that they let their pets bask in outdoor enclosures. If so (and assuming those cages are not glass), and if they can do this year round (eliminating all but the most southern extremes of our country), they may need no UV fixture. You should also mention that such set-ups must always allow the animal to retreat from the sun.


In a very general sense, UVB lighting is a 12 hour on/12 hour off routine (it’s very easy to run a timer in line with the fixture to make this automatic). Animals dependent on light cycle lengths to breed will need more specific regimens that replicate the seasons.


But, one rule of thumb: If the animal has adequate shelter from the light, cages can be lit 24/7. They will acclimate! Clearly this would not work well for a cage located in a bedroom, but otherwise, this might simplify a lot of people’s lives!


You can see that lighting is an issue for which each animal and every enclosure requires individual solutions. These can be reached only by having a thorough conversation with your client to determine what products best suits the pet’s needs. As with everything in our business, satisfying the customer with the right solution builds trust and solidarity in your relationship, and, most importantly, provides the best possible life for their pets.


And that’s worth it.  PB


Owen Maercks has enjoyed being immersed in the world of professional herpetoculture for nearly 40 years. His store, the East Bay Vivarium in Berkeley, Calif., is one of the oldest and largest herptile specialty stores in the U.S.