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 gets treated as too low-output to bother with.

Sounds like brand snobbery until you look at the failure mode. A weak UVB bulb doesn't look weak. It lights up like a good one, your dragon basks under it the same way, and the deficiency shows up months later in the animal's bones. No feedback loop catches the mistake, so keepers fall back on the two brands with a track record instead of trying their luck.

ReptiSun 10.0 or Arcadia 12%?

Both are correct. They trade blows.

• Price: the ReptiSun tube is far cheaper. Arcadia usually sells 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. Not better, 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 replace Arcadias every six months, and at least one had a 14% tube die inside a year.
• Availability: the quiet tiebreaker, and worse than it sounds. Arcadia replacement tubes are hard to source. Keepers repeatedly report that shops stock only the full kits, and one big-box chain dropped the line entirely. A bulb you can't replace 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% doesn't 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 "just buy the Arcadia 12%" often isn't an option you have, and we'd count that against it rather than file it as a footnote.

Our take: start with the ReptiSun 10.0 unless you already own an Arcadia fixture. Cheaper, easier to replace, and the pragmatic keeper view is that if the output is in the right range you buy whichever you can 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 on the box means

The 10.0, the 12% and the 14% aren't a quality scale, and higher isn't 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.

Keepers aim for a UV index somewhere around 4.0 to 4.5 where the dragon basks. That comes out of grade, distance and whatever sits in between, not the logo on the tube.

Get the length right

The tube should span roughly two thirds of the enclosure. People skip this rule because it costs more, and it matters more than the brand argument does. 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. Don't buy the cheaper short one and hope.

T5, not T8, and never a coil

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

Coil and compact bulbs are a separate trap. They light a fraction of the enclosure and won't stand in 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. That's the part people economise on before wondering why their numbers are low. The reflector aims the UV at the animal instead of the ceiling.

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. 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

The community splits here, and the split is worth seeing 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. Others replace theirs every six months, and one had a 14% tube fail inside twelve.

Nobody in the argument can see the output, which is why the argument never ends. UV decays invisibly, the light looks identical the whole way down, and the only instrument that settles it costs several times the bulb. So 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. Our Zoo Med ReptiSun T5 HO review goes further into that trade.

How to know it is working

You can't tell by looking, and you can't tell by the colour. The cheap UVB test cards sold next to the bulbs aren't considered reliable for reading real output. A UV index meter answers the question, and it costs many times what the bulb does, which is why most keepers don't own one and run on brand plus a calendar instead.

That's a reasonable way to live, as long as you're clear that it's trust and not verification. Keep several animals and the meter stops looking expensive.

Where we land

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 if your basking spot sits far from the tube.

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