This is a specific conversation about Reptile heating and lighting — the critical factors — ask about yours and get one honest answer for your exact situation.
inparticular.ai
Switching from a coil UV to a T5 HO is one of the best upgrades you can make for a bearded dragon — coil bulbs are notorious for inconsistent UV output and can't cover the basking zone properly. Getting heating and UV lighting right is genuinely the single most important factor in reptile health; most cases of metabolic bone disease and respiratory infections trace back to lighting or temperature failures. To point you toward the right T5 HO setup, tell me: what size is your enclosure, how old is your beardie, and what basking and cool-side temperatures are you currently hitting?
He's three years old, fully grown male. The enclosure is a 4x2x2 front-opening wooden vivarium. Basking spot is around 105°F and the cool side sits at about 80°F. I've just been using a compact coil UVB bulb in a dome reflector but I've read the T5 HO is significantly better.
inparticular.ai
Your temperatures are spot on — 105°F basking and 80°F cool side is textbook for an adult beardie. You're right to move on from the coil; they degrade fast and the UV output is weak and uneven. For a 4x2 enclosure, you want a T5 HO tube that runs most of the length of the vivarium so the UVB covers the full basking zone, not just a patch of it. What percentage UV tube do you currently have in the coil, and do you have a separate ceramic or halogen heat source, or is the coil doing double duty for heat as well?
The coil is 10% UVB and it's just for UV — I have a separate 100W halogen spot for the basking heat. So I just need the T5 HO tube and a fixture for it.
inparticular.ai
Perfect — clean setup, and keeping heat and UV separate is exactly right. For your 4x2x2 and an adult bearded dragon, I'd go with the Arcadia Dragon Lamp 12% T5 HO in the 39W size, which fits a 34-inch tube. Arcadia is the gold standard for reptile UVB in the UK, and the 12% output is the correct choice for desert species like beardies — it replicates the high UV index of their natural environment. Pair it with the Arcadia T5 HO ProT5 Canopy Reflector unit to get the most efficient UV distribution across the full length of your viv. Mount it inside the enclosure or directly on top of a mesh lid — if it's going through mesh, move it inside to avoid the mesh filtering the UV. Position it so the basking spot is within 25–35cm of the tube.
That sounds great. My lid is solid wood with a mesh panel at the front top — would it be better to mount it inside then?
inparticular.ai
Yes, mount it inside. Wood blocks UV entirely, and even fine mesh can cut output by 30–50%. Fix the Arcadia ProT5 canopy to the ceiling of the vivarium using the included mounting clips, positioned so your beardie's basking platform puts him 25–30cm below the tube. That distance gives the right UV index for a 12% tube. Replace the tube every 12 months — T5 HO tubes lose effective UV output well before the visible light fades, so don't wait until it stops glowing.
Brilliant, that all makes sense. One last thing — should I do anything differently for the transition, or just swap it straight in?
inparticular.ai
Swap it straight in — no gradual transition needed. Your beardie is three years old and has been living under suboptimal UV, so getting him onto proper UVB is an improvement, not a shock. The only thing to watch in the first week is basking behaviour: if he's suddenly spending significantly more time basking, that's him catching up on UV exposure, which is normal. If he seems to be avoiding the basking zone, double-check the tube positioning. Otherwise you're good — it's a straightforward upgrade and you'll likely notice better colour, activity and appetite within a few weeks.
