Best UVB lighting for bearded dragons

Bad lighting is the single most common husbandry mistake with bearded dragons — incorrect UVB output or basking temperatures are the leading cause of metabolic bone disease and chronic illness, and most owners don't realise anything is wrong until real damage has already been done. The fact that you're looking into UV index levels at seven months is exactly the right instinct. To give you a precise recommendation, can you tell me: what size enclosure is your dragon in, which UVB bulb are you currently running (brand and wattage if you have it), and roughly how old is the dragon?

Good setup, and you're right to question the T8. The ReptiSun 10.0 T8 is a decent bulb, but in a 4x2x2 enclosure the output drops off significantly with distance — by the time your dragon is sitting 30–40cm below it, the UV index is often well under 3, which is the low end of Ferguson Zone 3 where bearded dragons naturally sit. At seven months she's still actively mineralising bone, so this is genuinely the stage where UV intensity matters most. What's the distance from the bulb to her usual basking spot?

Yes — switch to the Arcadia T5 HO 12% Dragon lamp. At 35cm it delivers a UV index of around 4–6, which puts her comfortably in the middle of Ferguson Zone 3 where wild bearded dragons spend most of their active time. The T5 HO format produces significantly more output per tube than a T8 at the same wattage, and the 12% rating is specifically formulated for high-UV desert species like bearded dragons. You'll need a T5 HO controller unit if you don't already have one — Arcadia makes a compatible reflector unit that's worth getting because it directs the light downward rather than losing half of it into the ceiling of the viv. The bulb lasts 12 months before UV output degrades even if it's still visibly lit, so mark the date when you fit it.

At seven months, 14 hours of light and 10 hours of darkness is ideal — it mirrors her natural summer cycle and supports healthy appetite and activity. The key thing to get right alongside the bulb upgrade is basking temperature: surface temp at the basking spot should be 45–50°C measured with a temperature gun, not an ambient thermometer. If you haven't checked it that way, do it before anything else. UVB and basking heat work together — she needs both to synthesise D3 properly. Get those two dialled in and her bone development should be solid through adulthood.

Great move doing this now rather than waiting for symptoms. One last thing — when the new bulb is in, introduce her to the higher UV gradually over a week by slightly increasing the distance first, then lowering the platform to the right height. It's unlikely to cause photokeratitis but it's good practice with any UV upgrade. Mark the fitting date on the tube itself with a marker pen so you don't lose track. She'll be well set up.