How to Choose a UVB Bulb and the difference between T5 and T8 bulbs

This UVB lighting guide has been written by Christy Bruckner for Reptile Cymru to help you understand UVB lighting and find the right UVB bulb for your animal. If you’re looking for a very quick recommendation then please feel free to call us on 02920 190291, email us or send us a Facebook message. Please include your question, the species you’re housing, the age of it, and your enclosure size. We’ll let you know the most suitable bulb for you!

Introduction to UVB and Reptiles

If you keep reptiles you’ll definitely have heard of UVB – Ultra Violet B – light rays. In humans, these rays are what give us a suntan or sunburn, but in reptiles, UVB starts the process which synthesizes Vitamin D3. In turn, Vitamin D3 is essential for reptiles to process the calcium from their food and calcium is critical for their health, to avoid dangerous conditions like Metabolic Bone Disease. In short, UVB is a very important part of keeping healthy reptiles. In this article I’ll explain how you can pick the right UVB tube for your reptile to ensure they’re as healthy and happy as possible.

Depending on what species of reptile you have, their UVB needs will be different. This will vary based on whether they’re diurnal or nocturnal along with what part of the world they live in and how much UVB they receive in the wild. In the past reptile keepers thought that nocturnal animals didn’t need any UVB but recent studies have shown more and more that most previously described nocturnal reptiles are crepuscular (active at dawn and dusk) and would take advantage of some UVB in the wild at the safest times for them. The majority of researched species can show improvements in health, colouration, appetite and activity levels when presented with UVB even if they are not sun worshippers. When it comes to simulating this UVB lighting in captivity, we need to do it artificially in their enclosure. This can be done with bulbs which offer both UVB and heat, or more commonly, through long fluorescent tubes with some fantastic new products coming on the market in the last few years.

At Reptile Cymru we recommend UVB with all species where possible as best practice, but the UVB bulb you need is vastly different between diurnal and nocturnal species. For diurnal species it is critical and we will not sell them without the correct bulb in the enclosure because we know the animals health will suffer. UVB has only been commercially available for reptiles since 1993 and the technology is constantly improving and evolving. This is why in older care sheets you might find UVB is not recommended. We think it’s important to keep on top of all the scientific advances in reptile care and recommend based on the current best practice.

UVB Bulbs

Compact Bulbs – There are UVB bulbs available on the market such as the compact style Arcadia D3 Compact Lamp or coil Exo Terra Reptile UVB200. The advantage is they can fit in a standard E27 light fitting and can be used in a much smaller space than a UVB Tube. When looking at a compact lamp, you should also consider the positioning of the coils, we have found that you can get a significantly increased UVB output from the straight compact UVB bulbs such as the design Arcadia and Reptile Systems use if the bulb is being mounted sideways as in an Exo Terra Hood.

They do not offer the same output as a full tube and we generally wouldn’t recommend them in an enclosure that fits a tube but they do specifically fit into the Exo Terra Canopy Top Hood and can be very useful for providing UVB in an Exo Terra to a low output species such as amphibians or invertebrates.

MVB Bulbs – MVB (Mercury Vapour Ballast) are a high output heat bulb that also combines with UVB, for example the Arcadia D3 Basking Lamp which is available from 80w up to 160w. These also fit into E27 sockets rather than requiring a control unit and can be useful in larger enclosures where you want a direct high UV output and heat output together, targeted at a specific area over a high distance, ie 24-30″ height distance. It’s worth noting that these cannot be controlled with a thermostat which would usually be recommended with your heat output, so you need to be careful to avoid overheating.

In general, a compact coil UVB is used when an enclosure is too small to comfortably fit a tube, whilst an MVB might be used in an enclosure where the height is greater than a UVB Tube can penetrate.

We recommend that people gain the highest coverage across the vivarium as possible using a UVB Tube, but it’s great to have options on the market for when a tube isn’t appropriate. Assuming the majority of people will be looking for information about UVB Tubes, I’ll now walk you through some useful information about UVB Tubes to help you make your purchase.

UVB Tubes

In the majority of situations we recommend UVB tubes. UVB Tubes come in two fittings, T5 and T8, but what’s the difference between T5 and T8 tubes and which one should you buy for your reptiles?

T5 or T8 refers to the thickness of the fluorescent tube in eights of an inch. T5 Tubes have a circumference of 5/8ths of an inch, whilst T8 tubes have a circumference of 8/8ths of an inch (1inch!).

You might think that a larger tube produces more UVB and thus lean towards the T8, but the opposite is actually true, because T5 and T8 bulbs use different technology so the output is not based on the physical circumference of the tube. T5 Bulbs are actually higher output than T8.

T8 Tubes

These are the original UVB tubes that reptile keepers have been successfully using for decades, although in recent years, with more research into reptile care being done, new ranges have come out to suit a wide variety of species.

The T8 Tubes that we personally stock are:

• Arcadia Euro-Range Forest 5%
• Arcadia Euro-Range Desert 10%
• Arcadia D3+ Reptile Lamp, 12%
• Reptile Systems D3 5%
• Reptile Systems D3 10%

T5 Tubes

These newer tubes have only been around for a few years and despite being slimmer than the T8 tubes, actually have a higher output. They offer brighter and higher quality UVB light. We now stock Arcadia and Reptile Systems full range of T5 High Output Bulbs.

The T5 Tubes that we personally stock are:

• Arcadia D3 Reptile Lamp, 6%
• Arcadia D3+ Reptile Lamp, 12%
• Arcadia D3+ Reptile Lamp, 14%
• Arcadia Pro T5 Kit
• Arcadia Mini T5 Kit
• Reptile Systems D3 5%
• Reptile Systems D3+ 10%
• Reptile Systems Twin T5 Luminaire
• Zoo Med Repti-Sun T5 Terrarium Hood

If T5 are stronger wouldn’t I always buy a T5 tube?

No. T5 are higher output, but not all reptiles need this higher output so stronger is not necessarily better for every situation. It’s important to look at the size of the enclosure as T5 bulbs need to be further away from reptiles to be used safely. In enclosures that are 18″ or less in height, you are much more likely to want to use a T8 bulb (as your basking spot is likely to be elevated from the ground as well). If your enclosure is 24″ or higher, then you’re more likely to want to use a T5 bulb, but you still want to ensure you get the correct strength for the species.

How do I get the correct strength? UV Index

UVI – UV Index – is a measure of UV. Using the UVI of the wild location, we can analyse and compare it to the UVI of our vivarium with different bulbs and try our best to replicate what the reptile needs. A desert reptile such as a Bearded Dragon, compared to a rainforest reptile such as a Panther Chameleon require different UVI numbers. A nocturnal animal such as a leopard gecko, or a corn snake, will be dramatically different again.

So what UVB do I need for my species? How do I know what a Bearded Dragon needs compared to a Leopard Gecko?

Market leaders Arcadia Reptile have put together an extensive Interactive UV Index Lighting Guide. You can input your species and it gives you a guide for exactly which bulb to choose and the height it needs to be at. We recommend using this guide when deciding what strength bulb to purchase for your species.

Here is a quick example of the Bearded Dragon output chart:

You can clearly see that although the Bearded Dragon is a full desert species, if your distance from the height of the bulb to the reptile (not to the floor – but to where your bearded dragon will be sitting, for example on the rock in the photo below) is 10-12″ then you can still use a T8 12% UVB. However when you bring your height up to 12-18″ you want to switch to a T5 12% UVB bulb.

So when choosing your bulb, including the fitting and the strength, you need to know what species you’re putting in the enclosure, and the distance from the lamp to where the reptile will be sitting (not the overall height of the vivarium).

But what length do I choose?

You’ll also have noticed that UVB bulbs come in different lengths. In heating we always place our heating element on one side of the vivarium to create a gradient, but in UVB lighting it will depend on whether the animal is diurnal, crepuscular or nocturnal.

Diurnal – Active in the day – You want to get as much coverage across the whole of the vivarium. Usually you want your bulb to offer a good amount of coverage in the vivarium, but you also need to leave space for the tube fitting on either side of the bulb.

We stock Arcadia and Reptile Systems T5 UVB Tubes which come in 22″ (for a 24″ enclosure), 34″ (for a 36″ enclosure) and 46″ (for a 48″ enclosure). Additionally T8 tubes have some extra sizes in between to accommodate different size enclosures. You can use a smaller bulb if it still offers the coverage that you need, a 34″ bulb still offers good coverage in a 48″ enclosure.

Crepuscular / Nocturnal – Active at Dawn or Dusk (or Twilight), or Active in the Night – These are the reptiles that previously were not recommended UV, but it’s since been found that these animals will bask at dawn and dusk, or occasionally in the day. This means they get a partial amount of UV amidst shade. In these animals it’s not as critical that the UVB Tube be the full length of the enclosure as it’s important not to over expose them. Creating areas of shade or having a bulb more towards the basking area would be beneficial.

From research we now know that the vast majority of reptiles are crepuscular in the wild, and not truly nocturnal as previously thought.

What UV Control Unit do I need?

T5 and T8 bulbs need a different type of control unit, so you need to make sure you purchase one for the correct type of bulb. Then control units will have a wattage, and you need to make sure you choose the correct wattage for the length of bulb.

We sell a range of Control Units suitable for UVB. You will find that the control unit has a wattage on it, for example the Arcadia T5 Control Unit comes in 24w-39w. You should ensure your tube is within the correct range for the control unit.

We also sell the products such as the Arcadia T5 Mini UVB Kit which have the control unit and bulb built in but in the majority of situations you will be buying a tube and control unit separate.

How often do I need to replace my UVB Tube?

This is a complicated question that could use an article all by itself, but the easy answer is that you should change your tube as often as the manufacturer recommends. The manufacturer will have tested the output of the bulb over time and decided at what point a new bulb is required. This is generally from 9 to 12 months. You will notice that your bulb still gives out light, but the UVB rays, which we cannot see with the naked eye, will diminish over time. It’s only with a Solarmeter that we can detect and track these UV rays.

At Reptile Cymru we use a Solarmeter regularly in all our tanks to assess the UVI of each bulb and replace when needed as we deal with a large amount of reptiles and bulbs. In the home environment this isn’t practical as the meter itself retails for between £250 – £400. It is quite a high end piece of equipment and not necessary for the home reptile keeper. Therefore we recommend you always change your UVB bulb according to the manufacturer’s recommendation.

What are reflectors?

You may also have heard or read about reflectors. A reflector is a very simple piece of technology that can make a big difference in an enclosure. It’s basically a hood that goes above the UVB and is reflective aluminium. The UVB that would usually be hitting the top of the vivarium, which is wasted, will instead hit the reflector and bounce back down to the reptile. They are inexpensive, easy to fit and a very efficient way of ensuring all your UVB is directed in a useful way.

You want a reflector that is approximately the same length as your tube to fully reflect all of the rays, but if you use a smaller one it is fine. You will need either a T5 Reflector or a T8 Reflector depending on which tube you are using.

Help and Advice

So hopefully having read this far you’ve now get a better idea of what UVB tube you need for your species, whether it’s T5 or T8 and what equipment you’ll need to accompany it.

If you’re still not sure, no worries, Reptile Cymru offers free advice from our experienced staff, whether it’s about the best first time pet, the correct diet, housing, lighting or more. Give us a call on 02920 190291, email, or Facebook message with your question. Let us know as much detail as possible, including your question and what species you’re keeping or hoping to keep and the full dimensions of your enclosure. We’ll make sure you can find the right equipment to keep your reptile as healthy as possible.