Best UVB for Bearded Dragons: T5 vs Mercury Vapour

UVB is one of the most important things you will set up for a bearded dragon, and it is also one of the most misunderstood. Get it right and your dragon stays strong, active and healthy. Get it wrong and you can end up with serious health problems that are hard to reverse.

Two UVB lighting options are commonly used for bearded dragons: T5 high output tubes and mercury vapour bulbs. Both can provide UVB, but they work differently and have different installation requirements.

At Viperia, we generally recommend T5 high-output lighting for bearded dragons because it provides a broad, consistent area of UVB and can be positioned separately from the heat source. Mercury vapour bulbs combine UVB and heat in a single lamp, which can be useful in some setups but requires more careful positioning and monitoring.

This guide explains how the two options compare, why T5 is our usual recommendation, how to choose an appropriate UVB strength and position, and how to maintain the system as the lamp ages. The aim is to keep the advice practical, so you can make the right choice for your bearded dragon's enclosure.

What About Compact UVB and Metal Halide?

T5 and mercury vapour are not the only options on the shelf, and it helps to know where the others fit.

Compact UVB bulbs are small screw-in bulbs that cover only a little area. They can suit smaller enclosures or species with lower UVB needs, but for a bearded dragon in full-size vivarium they simply do not spread enough UVB to do the job well. Most beardie keepers are better served by a T5 tube or a mercury vapour bulb.

Metal halide bulbs sit at the premium end. Like mercury vapour, they combine strong UVB, bright visible light and heat in one unit, with excellent light quality that really shows off a dragon’s colour. They share the same all-in-one trait, so heat and UVB are linked. They are worth a look for larger, showpiece setups. Viperia stocks both compact UVB and metal halide UV, so if they fit your plans, we can talk you through it.

Getting the Strength Right: Ferguson Zones

UVB is not one-size fits all. Different reptiles evolved under different amounts of sun, and these needs are grouped into what are called Ferguson Zones. Bearded dragons are high-UV baskers, sitting near the top of that scale, which is why they need a strong, desert-strength source rather than a gentle one meant for a shade-dwelling species.

The practical measure is the UV Index, or UVI, which tell you how strong the UVB actually is at a given spot. For a bearded dragon you are aiming for a meaningful UVI at the basking spot, commonly cited somewhere around 3 to 6 depending on the guidance you follow, with weaker readings across the rest of the enclosure so your dragon can choose how much it takes. Bulb and tube makers publish mounting distances to help you hit the right zone, so follow their guidance for the exact product.

If you want to know your real numbers, rather than trust the box, a UV index meter reads the output at the basking spot. Viperia stocks solarmeters for keepers who like to measure and be sure, and our team can help you match a tube or bulb to your enclosure so the strength lands where it should.

So Which Should You Choose?

For bearded dragons, our usual recommendation is a T5 high-output UVB tube paired with a separate basking bulb. This allows UVB and heat to be positioned and controlled independently, while providing a broad area of UVB within the enclosure. The combination also makes it easier to create distinct basking and cooler areas.

The same basic approach can be adapted to different enclosure sizes and heights by selecting an appropriate T5 tube and UVB output for the setup. The important factors are not simply the bulb type, but the distance between the dragon and the lamp, the enclosure layout and the amount of UVB reaching the basking area.

Mercury vapour bulbs combine UVB and heat in a single lamp and can work in some setups. They may be considered where a suitable enclosure height and stable ambient conditions allow the lamp to operate at the required distance. However, combining heat and UVB in one source means that the two cannot be adjusted independently. 

Temperature is also more difficult to control precisely than with a separately thermostated heat source.

For that reason, we generally recommend T5 UVB with separate heating for new bearded dragon setups. If a mercury vapour system is already in use, it can still be assessed as part of the overall enclosure rather than automatically replaced. The correct choice depends on the enclosure dimensions, lamp position, temperature gradient and the equipment being used.

Running Costs Over Time

Cost is a fair thing to think about, because UVB is not a one-off purchase. Both routes need replacing, just in different ways.

The T5 route has a few more parts at the start, since you buy the tube, the controller and reflector, and a separate basking bulb. But the running side is kind. When the UVB fades you only replace the tube, which is an inexpensive part, and the fixture keeps going for years. The mercury vapour route is simpler to buy, being one unit, but when it is time to replace it you are replacing your heart and your UVB together in a single, pricier bulb.

Over a dragon’s lifetime, the T5 route usually works out the more economical of the two, which is one more reason it gets our recommendation. Viperia carries the replacement tubes and bulbs for both, so whichever way you go, keeping it topped up is straightforward.

Position the UVB With the Heat

Here is a point that catches a lot of keepers out. your dragon should be able to bask in heat and UVB at the same time, in the same place. In the wild, the sun delivers both together, so a dragon that basks is also soaking up UVB without thinking about it.

If you run a T5 tube, mount it over the warm end so it lines up with your basking bulb. That way your dragon gets its UVB while it basks under the heat. Put the UVB at the cool end and your dragon may rarely go near it, which defeats the point. With a mercury vapour bulb this is handled for you, since the heat and UVB come from the same spot, but it is worth double-checking the basking ledge sits in that zone.

Distance, Mesh and Shade

How you fit your UVB matters as which one you buy. A few points to keep your dragon safe and your UVB effective:

·       Mind the distance. Every UVB source has a recommended mounting distance from where your dragon basks. Too far and the UVB is took weak; too close and it can be too strong. Follow the manufacturer’s guidance for your bulb or tube.

·       Account for mesh. If UVB has to pass through a mesh screen, it loses a fair amount of it’s strength, often a third or more. Mount UVB inside the enclosure where you can or factor the mesh into your distance.

·       Give shade. Your dragon needs to be able to get out of the UVB as well as into it, so make sure there is a shaded retreat at the cool end.

·       Keep it inside. UVB does not travel through glass or standard plastic, so the source must be within the enclosure, not outside the lid.

How Many Hours a Day?

Bearded dragons need a clear day and night rhythm, so your UVB and daytime lighting should run for a set stretch day and then switch off completely at night. Somewhere around 10 to 12 hours a day suits most keepers, and a simple pug-in timer takes the job off your hands, so it is consistent.

Some keepers shorten the hours a little in winter to mirror the changing seasons, which can be part of a natural seasonal slowdown. Whatever you settle on, keep the night genuinely dark, since a proper rest period matters as much as the daytime light.

UVB Fades, So Replace It on Schedule

This is the mistake that catches people out. A UVB tube or bulb keeps producing visible light longer after its UVB has faded away. So a bulb that looks perfectly fine can be giving your dragon almost no usable UVB. You cannot judge it by eye.

As a rule, plan to replace your UVB around every 12 months, or sooner if the manufacturer advises it. Write the date on the tube or bulb when you are fitting it so you’re not guessing later. If you want to be certain, a UV meter measures the actual output so you can see exactly when it is time to change.

Viperia stock radiometers for keepers who like to check rather than assume, and we carry replacement T5 tubes and mercury vapour bulbs so keeping on top of it is easy.

Signs Your Dragon May Not Be Getting Enough UVB

Because UVB problems build slowly, it helps to know the early warning signs. If a dragon is short on usable UVB over time, you may notice it becoming lethargic and reluctant to move, losing its appetite, or trembling and twitching in its limbs. In more advanced cases you might see soft or swollen jaws, or legs that look bent or bowed, and difficulty lifting the body to walk.

These are signs of metabolic bone disease, and they are a reason to act rather than wait. Check your UVB setup, its ages, distance and position, and speak to an exotics vet if you have any concern. Caught early, a lot can be turned around.

Common UVB Mistakes We See

·       Relying on a basking bulb alone and assuming it provides UVB. It does not.

·       Shining UVB through glass or a window, which blocks it almost completely

·       Leaving a tube or a bulb in place for years because it still lights up, long after the UVB has faded.

·       Mounting the UVB too far from the basking spot, so the dragon rarely basks under it.

·       Fitting the UVB at the cool end, away from the heat, so the dragon rarely basks under it.

·       Trying to run a mercury vapour bulb through a thermostat, which does not work.

·       Using a weak, low-output UVB source for a species that needs strong, desert-strength lighting.

Getting It Right, With a Hand from Viperia

UVB comes down to a few clear things: a strong, desert-strength source, the right distance from the basking spot, the UVB positioned over the heat, a shaded retreat to escape into, and a replacement on schedule before the output fades. For a bearded dragon, the setup that delivers all of that with the least fuss is a T5 tube with a separate basking bulb, and that is what we recommend.

If the choice feels like a lot to weigh up, that is what we are here for. Viperia stocks the full range under one roof, from T5 UVB tubes, controllers, canopies and reflectors to radiometers and the calcium supplements to go alongside, plus the basking heat and PVC vivariums to complete the setup.

Please get in contact with our team if you have any further questions and we will be happy to help.