Welcome to the Bio Dude. Spend $100 get $14.95 Flat Rate Shipping! Your #1 source for all reptile supplies. Expect carrier delays due to COVID19. NOTICE: We currently cannot ship live plants to California.
Introduction to UVB, part 2

Introduction to UVB, part 2 0

Introduction to UVB, part 2:

How to Use UVB in Your Reptile Enclosure

Guest post written by ReptiFiles for use by The Bio Dude

Over the course of millions of years of evolution, every reptile has specifically and remarkably adapted to a specific type of environment and lifestyle. Under ideal circumstances, we would all be able to keep our reptiles outdoors in the exact same environment that they evolved in and wouldn’t have to artificially provide heat or UVB.

As pets, our beloved reptiles are far removed from their natural habitat in the wild and require our care. So it’s up to us to recreate allaspects of the habitat that they evolved in: temperatures, humidity, UVB, substrate, diet, territory size, etc. When we succeed in this effort, we enable them to truly thrive (not just survive) in captivity.

Both UVA and UVB are present in all reptiles’ natural habitats. However, the exact amount of UVB that is present varies from habitat to habitat. Different types of reptiles from different microclimates require different levels of UVB. There is no one-size-fits-all solution. You can’t walk into a pet store, grab whatever UVB bulb looks good, and walk out. However, most reptiles fit into one of four categories:

Meet the Ferguson Zones

Dr. Gary Ferguson categorized the different levels of UVB need into 4 zones, and revolutionized the way we approach UVB provision for reptiles.

Zone 1describes crepuscular reptiles and shade-dwellers that thrive with a UV Index between 0.1-0.7.

  • ball pythons
  • corn snakes
  • crested geckos
  • leopard geckos

Zone 2describes partial sun and occasional baskers that thrive with an average UV Index of 0.7-1.0.

  • red-footed tortoises
  • green anoles
  • Chinese water dragons
  • boa constrictors

Zone 3describes open and partial sun baskers that thrive with an average UV Index of 1.0-2.6.

  • red-eared sliders
  • day geckos
  • blue tongue skinks

Zone 4describes mid-day open sun baskers that thrive with an average UV Index of 2.6-3.5.

  • bearded dragons
  • uromastyx
  • chuckwallas

*Note that these are all-day averages, not maximums or total gradient specifications.

If you keep a reptile species that is not on this list, reference Frances Baines’ UV Tool to find the Ferguson Zone categorization, recommended UVI, and optimal lamp for your pet’s needs.

What are these numbers?

UV Index, or UVI, is how we measure UVB radiation. It was initially developed by the World Health Organization, United Nations Environment Programme, and the World Meteorological Organization as a way to raise awareness of the risks of excessive exposure to sunlight, and to alert people of when and where the sunlight is strong enough to cause skin damage.

Although initially created for human health, UVI is also very helpful for measuring the levels of UVB that wild reptiles expose themselves to and how much we’re giving them in captivity. The Solarmeter 6.5, Solarmeter 6.5R, and Zoo Med Digital UV Index Radiometerare devices that can be used to measure the UVB output of the lighting anywhere in a reptile’s enclosure. If you are serious about reptile keeping, it’s a good idea to invest in one of these devices to fine-tune your husbandry.

Types of UVB bulbs

UVB bulbs generally fall into 3 different categories: linear fluorescents, compact/coil fluorescents, and mercury vapor bulbs.

Linear fluorescent UVB bulbs

Linear fluorescents come in two types: T8 and T5 HO. The number indicates the diameter of the fluorescent tube, as well as the power.

  • T8 bulbsare older technology and produce less powerful UVB. They also tend to have shorter lifespans, lasting about 6 months before needing to be replaced.
  • T5 HO (high output) bulbsare a newer technology and produce stronger UVB that penetrates further into an enclosure. They also last at least 12 months before needing replacement.

Linear fluorescents should be mounted inside a reflective light fixture appropriate to the size and power of the bulb for optimal output and lifespan. Reflective T5 HO fixtures aren’t cheap, but they’re an essential investment.

T5 HO UVB bulbs are the most popular type of UVB lighting in the reptile hobby because they work well with a variety of enclosure sizes and reptile species. They are also the preferred source of UVB lighting at reputable zoos.

The best linear fluorescent UVB bulbs in the US are made by Arcadia and Zoo Med.

Compact/coil fluorescent UVB bulbs

Compact and coil fluorescent UVB bulbs are like T5 UVB bulbs that have been folded and twisted around themselves to fit in a standard incandescent bulb socket. They are less powerful than T5 HO or even T8 linear bulbs at the same distance, but they can work well in small enclosures 12-18” tall and less than 24” wide. You will usually see them available in two sizes: 13w and 26w. Lifespan is between 6-12 months, depending on brand. For best results, use with a reflective fixture.

The best manufacturer of compact and coil fluorescent UVB bulbs in the US is Zoo Med.

Mercury vapor & metal halide bulbs

Mercury vapor and metal halide bulbs are unique because they produce heat, visible light, UVA, and UVB all in one bulb. This also makes them very appealing to most reptile keepers at first glance.

  • Mercury vapor bulbs (MVBs)project intense UVB and heat further than many other types of UVB bulb, making them popular for particularly tall enclosures. But even the best MVBs tend to fluctuate in output from one bulb to the next, and use a relatively short wavelength of UVB compared to other sources, which makes them potentially dangerous and distrusted by many experts. High quality bulbs can last 12 months or more.
  • Metal halide bulbsare extremely bright and have a particularly high UVA output compared to other UVB bulbs. Some consider them to be the best sunlight simulators, although they must be positioned at a greater distance than other bulbs for safe use. They also require external ballasts and a fixture that can cope with their high-voltage ignition pulse. Unfortunately, UVB production decays fairly quickly in these bulbs.

Although they seem convenient, mercury vapor and metal halide bulbs tend to be extremely limiting because they don’t allow for independent control of heat and UVB. This makes them a better fit for some reptiles rather than others, and requires the use of a Solarmeter and an accurate digital thermometer for safe positioning and use.

If you use mercury vapor or metal halide bulbs, you must use bulbs that were specifically designed for use with reptiles. Otherwise they can seriously harm your reptile. They also require lots of air circulation around the bulb to prevent overheating (no dome fixtures) and break easily when bumped during use.

The best mercury vapor and metal halide bulbs available in the US are by Arcadia and Mega-Ray.

Are brands other than Zoo Med, Arcadia, or Mega Ray okay to use?

At this point, the evidence is not strong enough for me to recommend other brands such as Zilla, Exo Terra, All Living Things, etc. Most are simply weaker than advertised or run out of UVB more quickly than higher quality options, or have inconsistent output. However, some (especially off brands you may be tempted to buy for cheap online) actually produce UVC radiation, which is VERY dangerous to your pet.


How to use your UVB bulb properly

Okay, now you know what UVB is, how it works, the different types of bulbs, and which brands are best. But if you don’t use your bulb(s) properly, all of this money and effort will be wasted and you could end up hurting or even killing your pet. So here’s how to do UVB rightin your reptile’s enclosure:

Placement is everything!

UVB bulbs should always be mounted on the ceiling of the enclosure, like the sun in the sky. But there’s more to it. When figuring out where to put your UVB, ask yourself the following four questions:

  1. Is the bulb installed over or under the mesh? Mesh blocks a significant amount of UVB.If your enclosure has a mesh ceiling, your UVB bulb and fixture should be installed on the underside of this mesh, not over it.
  2. Is there glass or plastic covering the bulb?Glass and plastic block all UVB. Remove any protective glass or plastic bulb covers that the fixture may have come with before using.
  3. Are the heat source and UVB lamp on the same side of the enclosure?Heat and UVB always go together. These two factors need each other for the reptile’s body to make the vitamin D that it needs, and keep in mind that in the wild, sunlight delivers both heat and UVB wherever it is found. So for example if your heat source is on the far left side of the enclosure, the UVB should also be placed to the far left so its beam overlaps with the beam of the heat source.
  4. How far will the UVB bulb be from your reptile? There is an inverse relationship between UVB strength and how far away your reptile is from the source. If closer, then the UVB it experiences will be stronger. If further, then the UVB it experiences will be weaker. Pay attention to the recommended distance listed on the bulb’s packaging, and position your basking areas accordingly.

Use the right fixture

Each type of UVB bulb needs a specific type of fixture to work properly. Follow the directions on the bulb packaging, and don’t try to take shortcuts. If the bulb is available in a kit that includes the fixture or the manufacturer offers a fixture that goes with the bulb, buy that one.

Don’t forget the reflector

Fluorescent UVB bulbs must be used with a reflective light fixture, and preferably one that has been polished to a mirror finish. Otherwise 50% of the UVB produced will go into the fixture rather than getting reflected down into the reptile’s enclosure.

Replace the bulb on time

UVB bulbs don’t last forever. Almost from the moment you turn the bulb on for the first time, its UVB output will gradually decline until it’s just an ordinary lightbulb. Don’t try to save money by using the bulb for as long as it produces light — look at the manufacturer recommendations (usually 6-12 months), write the purchase date on the bulb, and be ready to replace it when it needs replacement.

Give your reptiles opportunities to escape the UVB

In the wild, reptiles will seek shade when the sun gets too strong or when they’ve had enough for the day. Similar to how they move between warmer and cooler areas to thermoregulate, reptiles also photoregulate by moving from sunlight to shade and everywhere in between.

Your UVB lamp should not span the entire length of the enclosure, but rather only part of its length. John Courteney-Smith of Arcadia Reptile calls this “the Light and Shade Method.” The exact ratio of light to shadow will vary from species to species — for example, a bearded dragon will need its UVB lamp to be about 2/3 as long as the enclosure, but a leopard gecko’s lamp will only need to be 1/4 to 1/2.

Adjust your supplements

When you are using a UVB bulb at the correct strength for your reptile’s species, its body makes all the vitamin D that it needs, so you don’t need to supplement it in the diet. Use plain, D3- and phosphorous-free calcium powder for dusting on insects.



There will always be people who claim that UVB is “optional” or that certain species just “don’t need it.” But as our understanding of reptile health and husbandry improves, it is becoming increasingly clear that we must consider UVB not just a beneficial option, but a necessity, and included with heat, humidity, and other key elements as a requirement of adequate husbandry.


References and Resources:

These are the resources that I referenced while writing this mini-series. I was only able to skim the surface here, so I highly recommend reading through the following for more in-depth information on UVB and related subjects. However, pay attention to publication dates, as although these are great sources, some are more up-to-date than others.

  • How much UV-B does my reptile need? The UV-Tool, a guide to the selection of UV lighting for reptiles and amphibians in captivityby Frances Baines et al.
  • Fire — The Sun: Its Use & Replication Within Reptile Keepingby John Courteney-Smith
  • Evaluating the Physiologic Effects of Short Duration Ultraviolet B Radiation Exposure in Leopard Geckos (Eublepharis macularius)by Amelia Gould et al.
  • Effects of ultraviolet radiation on plasma 25-hydroxyvitamin D3 concentrations in corn snakes (Elaphe guttata)by Mark J. Acierno et al.
  • An In-Depth Look At UV Light And Its Proper Use With Reptilesby Dr. Frances Baines, MA, VETMB, MRCVS
  • com
  • co.uk

About the author: Mariah Healey has been passionate about animal research from a young age. Today, she is a reptile husbandry specialist and the author of ReptiFiles.com, where she publishes her findings on the best practices in modern reptile care. ReptiFiles is the most comprehensive, accurate source of reptile care on the internet, boasting 15 science-based guides to date, with two more in active development.

Introduction to UVB and reptiles, part 1

Introduction to UVB and reptiles, part 1 0

Introduction to UVB, part 1:

What is UVB, and Why is it Important to Reptile Husbandry?

Guest post written by ReptiFiles for use by The Bio Dude

Among experts, you can’t talk about reptiles for very long without bringing up UVB. And yet despite this essential component of reptile husbandry, there’s still a lot of misunderstandings and misinformation about it. The only way to get past confusion and misinformation on any topic is by seeking to understand how it works, so in this two-part article we’re going to talk about the basics of UVB: what it is, why it matters, and how to utilize it better in your own husbandry.

What is UVB?

When you think about our Sun, what comes to mind? If you’re like most, probably bright light, intense summer heat, and sunburns. But it’s more complicated than that. As a blazing ball nuclear fusion reactions, the Sun produces many different forms of energy, including little energy particles called photons. Photons move in waves at different speeds, and their speed determines how much energy they carry and how they function. This is called the electromagnetic spectrum:

  • Radio waves
  • Microwaves
  • Infrared light
  • Visible light
  • Ultraviolet light
  • X-rays
  • Gamma rays

As reptile keepers, we are most interested in infrared (heat), visible light (daylight), and ultraviolet light.


Of the three, infrared is the lowest-energy wavelength. Humans can’t see infrared, and most reptiles can’t either, but we all feel it as heat. There are 3 types of infrared: IR-A, IR-B, and IR-C.

  • IR-A— Highest in energy. This is the primary type of infrared produced by the Sun, and penetrates deepest into surfaces like animal tissues. That deep, “ahhh” feeling you get when you step out into the sun on a nice day? That’s IR-A at work.
  • IR-B— Contains a medium amount of energy. This is the secondary type of infrared produced by the Sun, and penetrates surfaces well, but not quite as deeply as IR-A.
  • IR-C— Lowest in energy and does not penetrate very deeply into surfaces, if at all. IR-C is actually not produced by the Sun. It’s actually a byproduct produced when IR-A and IR-B wavelengths have come in contact with a surface that has absorbed some of their energy. This is the ambient heat you feel on hot asphalt or a warm summer night.

I’d love to go more into detail on this subject, as proper reptile heating is even more important than proper reptile lighting, but this is an article on UVB, not heat, so we’ll leave that for another day.

Visible light

Visible light is the range of wavelengths that humans perceive as light and color, between 400-700nm. The exact wavelength of visible light is what we perceive as different colors of light, which is measured in Kelvin. It is also associated with the light’s intensity, or brightness. Artificial light sources generally range from about 1,900K (dim and warm) to 10,000K (extremely bright and blue). Many consider 6500K to be optimal for best plant growth and truest color perception.

Ultraviolet light

Ultraviolet is the highest-energy wavelength that we regularly use as reptile keepers, and completely invisible to humans. Like infrared, UV is broken down into 3 distinct categories: UVA, UVB, and UVC.

  • UVA— With a wave length of 315-400nm, UVA is a low-energy form of ultraviolet. This light is invisible to humans, but it is visible to some animals, including reptiles. UVA can pass through glass and clear plastic.
  • UVB— With a wave length of 280-315nm, UVB is a high-energy form of ultraviolet. It is partially filtered by Earth’s atmosphere and is blocked by glass and plastic. It can damage cellular DNA with prolonged exposure, causing sunburn in humans. It is also essential to the process of vitamin D synthesis and metabolism in many animals, including humans and reptiles.
  • UVC— With a wave length of about 180-280nm, UVC is the highest-energy form of ultraviolet. This wavelength destroys DNA on contact, and would destroy all life on Earth if it weren’t completely filtered out by our atmosphere. For this reason, artificial UVC-emitting lights are often used for disinfecting in devices such as toothbrush cleaners and air purifiers. This process is known as “irradiation,” and no, it doesn’t turn foods or objects radioactive.
Why is UVB so crucial to captive reptile husbandry?

Although UVA is important to many aspects of reptile life and shouldn’t be ignored, it is always included in artificial UVB lamps, and again for the sake of brevity we have to focus on UVB from this point.

As mentioned in the previous section, UVB (combined with heat) is required for the creation of vitamin D, and in turn, it is required for the healthy function of many associated metabolic processes. After getting processed into its usable form by the liver, vitamin D plays essential roles in a reptile’s brain, heart, lungs, kidneys, bones, immune system, and digestive system.

Additionally, UVB exposure plays an important role in boosting immune response, stimulating beta endorphin production, and increasing pigmentation (color).

UVB lamps are expensive. Why not just give them vitamin D in their food?

  1. Because “homemade” vitamin D is more available for the reptile’s body to use, and thus more effective. In one study, corn snakes exposed to UVB had higher (read: healthier) levels of vitamin D than those which had no UVB lighting and only received vitamin D from their food.
  2. Because it’s too easy to overdose or underdose supplementary vitamin D. Unlike with humans (and even that understanding could still use some work), we don’t have enough data on the exact amounts of vitamin D that each reptile species requires per gram of weight at each stage of life. Vitamin D is toxic in large amounts, causing a variety of severe symptoms, including kidney damage, calcification of soft tissues, and premature death. Underdose results in the softening of bones, malfunction of the digestive tract, nerve damage, and premature death.
  3. Because cellular vitamin D production is self-regulating, so when adequate UVB lighting is provided, it is impossible for a reptile to develop a vitamin D deficiency or toxicity. The reptile creates exactly the amount of vitamin D that its body needs.

But isn’t UVB dangerous since it causes sunburns and cancer in humans?

A lot of people think of UVB as a bad thing because it causes sunburns, and the associated cellular damage can lead to skin cancer (thanks propaganda!). But humans needUVB.

The Sun is one of the essential elements that makes life on Earth possible, and all life has evolved in varying responses to the availability of this resource, protecting themselves from the bad while making use of the good. Reptiles evolved scales, birds have feathers, cats and dogs have hair, and humans have…well, we exchanged our body hair for clothes.

Most humans in the US are vitamin D deficient because we’re indoors all day and anti-skin cancer propaganda has us afraid to go out in the sun without sunscreen. Vitamin D pills help, but studies are indicating that we need way more vitamin D than previously thought in order to replace sunlight. If roles were reversed and reptiles were keeping pet humans, we would need artificial UVB lighting too.

Furthermore, reptiles will also move into the shade when sunlight gets too intense or they’ve had their fill. Even sun-loving lizards like bearded dragons, chuckwallas, and uromastyx do most of their basking early in the morning and then find a hiding place by midday when the sun it at its strongest.

But some reptiles don’t need UVB, right?


If you keep snakes or crepuscular lizards like crested geckos or leopard geckos, you may have heard people emphatically assert that these species “don’t need UVB,” that it’s a “waste of money,” that it “hurts their eyes,” etc.

This is a very outdated approach, and more folklore husbandry than scientific fact. In fact, a mounting number of modern studies are proving the benefits of providing UVB to captive species that don’t ordinarily get UVB. Remember the corn snake study I referred to earlier? That’s just the tip of the iceberg.

Outside of formal research, many reptile keepers have observed daytime basking behavior in nocturnal species that have been provided with UV lighting. Although they may not bask as openly as bearded dragons and red-eared sliders, they will cryptically bask by strategically exposing parts of their bodies to UV while keeping the rest hidden. This is a strategy evolved in the wild to help them get benefits from sunlight without making themselves vulnerable to predators.

When in doubt, keep in mind that all reptiles are exposed to the sun at some point or other in their natural habitat. Even those that seem to spend most of their time in holes or caves are indirectly exposed to small amounts of beneficial sunlight that reflects off rocks and other surfaces in the environment and into their hiding space.

**I should acknowledge here that albino, thin-scaled morphs, and other reptiles with reduced or no pigmentation are more sensitive to UVB as well as visible light, and will need exposure reduced accordingly. They don’t need the same amount of UVB to get the same benefit. Normal levels of light and UVB can lead to sunburn, blindness, and cancer in these animals.**

About the author: Mariah Healey has been passionate about animal research from a young age. Today, she is a reptile husbandry specialist and the author ofReptiFiles.com, where she publishes her findings on the best practices in modern reptile care. ReptiFiles is the most comprehensive, accurate source of reptile care on the internet, boasting 15 science-based guides to date, with two more in active development.

Review The Dude

Review some of the Dude's products and be submitted for a $25 BioDude gift card drawn at the first of each month! Each review gets you one submission.

Diggin' the Dude? Sign up.

The Dude will never spam you. Just periodically send information regarding awesome specials and information.