Best UVB Bulb for a Bearded Dragon

The two brands worth buying

Hundreds of reptile UVB products exist. The recurring keeper line is that only Arcadia and the Zoo Med ReptiSun are tested enough to trust, with Exo Terra's T5 now edging onto the list, and that the standard answer is the ReptiSun T5 HO 10.0 or the Arcadia 12%. Everything outside that is treated as too low-output to bother with.

That sounds like brand snobbery until you understand the failure mode. A weak UVB bulb does not look weak. It lights up exactly like a good one, your dragon basks under it exactly the same, and the deficiency shows up months later in the animal's bones. There is no feedback loop to catch the mistake, which is why keepers fall back on the two brands with a track record instead of trying their luck.

ReptiSun 10.0 or Arcadia 12%?

This is the actual decision, and the honest answer is that both are correct and they trade blows.

• Price: the ReptiSun tube is dramatically cheaper. The Arcadia is usually sold as a complete fixture kit, which is more to swallow up front, though you're getting the hardware too.
• Output: the Arcadia 12% runs hotter than the ReptiSun 10.0. That's not "better", it's different: the ReptiSun is a known safe, reliable bulb with slightly lower output, so it may want mounting a little closer.
• Lifespan: contested. Some keepers report the Arcadia holding usable output far longer than the Zoo Med and treat that as the reason to pay more. Others are replacing Arcadias every six months, and at least one had a 14% tube die inside a year.
• Availability: the quiet tiebreaker, and it is worse than it sounds. Arcadia replacement tubes are genuinely hard to source: keepers repeatedly report that shops only stock the full kits, and one big-box chain dropped the line entirely. A bulb you cannot replace on the day it dies is a bulb your dragon does without.

How bad is that in practice? Checking the day this was written, Arcadia's 12% simply does not exist as a four-foot kit you can reliably buy: the 36 inch 12% reads as unavailable, the smart-fixture version has no seller at all, and the 24 inch 12% is down to a single unit. The one Arcadia that fits a standard 4x2x2 off the shelf is the 14%, which is more output than that tank needs. So the honest version of "just buy the Arcadia 12%" is that you often can't, and that is a real strike against it rather than a footnote.

Our take: start with the ReptiSun 10.0 unless you already own an Arcadia fixture. It's cheaper, it's easier to replace, and the pragmatic keeper view is that if the output is in the right range you buy whichever you can actually get hold of. Pay up for the Arcadia when your basking spot is far from the tube and you need the headroom.

What the number actually means

The 10.0, the 12% and the 14% are not a quality scale, and higher is not better. They describe how much UV comes off the tube, which you then match to how far the animal sits from it.

• In a standard 4x2x2, 12% (or the ReptiSun 10.0) is the normal answer.
• 14% exists for basking zones more than about two feet from the bulb. Most shops have stopped carrying it.
• 5.0 and the low percentages are forest-species bulbs. Wrong animal, wrong tank.

The target keepers aim for is a UV index somewhere around 4.0 to 4.5 where the dragon actually basks. That is a function of grade, distance and what's in between, not of the logo on the tube.

Get the length right

The tube should span roughly two thirds of the enclosure. This is the rule people skip because it costs more, and it matters more than the brand argument: a short bulb over a long tank means your dragon can spend half its day on the unlit side getting nothing, which quietly recreates the problem you bought the bulb to solve.

Measure the tank, then buy the tube that fits it. Do not buy the cheaper short one and hope.

T5, not T8, and never a coil

T5 and T8 describe the tube diameter, and the difference is not cosmetic. T8 is the older standard: weaker, shorter effective range, and needing replacement about twice as often. Keepers also point out that a T8 cannot punch through a mesh screen at all, while a T5 can, at some cost in output. T8 bulbs are also getting hard to find, which settles it for anyone buying new.

Coil and compact bulbs are a separate trap. They light a fraction of the enclosure and are not a substitute for a linear tube, whatever the packaging says, and yes, the ReptiSun name is on some of them.

The bulb is only half the purchase

A bare tube does nothing on its own. It needs a T5 HO fixture, and the fixture needs a reflector inside it, which is the part people economise on and then wonder why their numbers are low. A reflector is not a luxury feature, it's what aims the UV at the animal instead of the ceiling.

If you're starting from nothing, a hood or a kit that bundles the tube and the fixture is usually the cheaper path than buying them separately. If you already own a fixture, buy the bare tube. And the two brands are cross-compatible, so a ReptiSun tube will drop into an Arcadia fixture later if you change your mind.

When to replace it, and why nobody agrees

Here the community genuinely splits, and it's worth seeing the split rather than a made-up number. Zoo Med's box says a year for a T5. Keepers commonly quote about twelve months for a T5 against six for a T8. Some report Arcadias running well beyond that, while others replace theirs every six months and one had a 14% tube fail inside twelve.

The reason for the disagreement is that nobody in the argument can see the output. UV decays invisibly, the light looks identical the whole way down, and the only instrument that settles it costs several times the bulb. So the practical answer: write the install date on the tube in marker and replace on the manufacturer's interval. Replacing a little early costs a few dollars; replacing far too late costs the animal. If you want to see our longer take on that trade, our Zoo Med ReptiSun T5 HO review goes into it.

How to know it is working

You cannot tell by looking, and you cannot tell by the colour. The cheap UVB test cards sold next to the bulbs are not considered reliable for reading real output. The only instrument that genuinely answers the question is a UV index meter, and it costs many times what the bulb does, which is why most keepers do not own one and run on brand plus a calendar instead.

That's a reasonable way to live and it's worth being honest that it's trust rather than verification. If you keep several animals, the meter stops looking expensive quite quickly.

The bottom line

Get a ReptiSun T5 HO 10.0 sized to two thirds of your tank, in a fixture with a reflector, and write the date on it. Buy the Arcadia 12% kit instead if you need the hardware anyway or your basking spot is far from the tube.

Then stop optimising. The gap between the two right answers is small. The gap between either of them and the bulb that was cheapest on the shelf is the one that matters.