Bearded dragon lighting at 5 years old

Five years is a great milestone — and honestly, reviewing the lighting setup at this point is exactly the right call. Bad lighting is the most common husbandry mistake with bearded dragons, and the damage from incorrect UVB or basking temperatures often shows up gradually as metabolic bone disease or chronic immune issues that owners don't catch until things are quite serious. To give you useful advice, I need a few details: what size is the enclosure, what UVB and basking bulbs are you currently running (brand and wattage if you know them), and has your dragon's behaviour or appetite changed at all as they've gotten older?

Good that you're thinking about this now. The ReptiSun 10.0 T8 is a decent bulb, but in a 4x2x2 the T8 format struggles — the UVI output at basking distance (usually 30–40cm below the tube) sits around 1–2 UVI, which is on the low end for a bearded dragon. For a five-year-old, you ideally want a consistent 3–4 UVI in the basking zone. How high is the basking spot from the floor, and is the UVB tube running the full length of the enclosure or just part of it?

That explains a likely UVB shortfall. At 25cm with a T8 10.0, you're probably getting adequate UVI at that specific spot, but the coverage is limited and T8 output degrades faster than most owners realise — if that bulb is more than 6 months old, it may already be producing significantly less UV than the label suggests, even if it still looks bright. For a dragon entering middle age in a 4x2x2, I'd switch to the Arcadia T5 HO 12% — specifically the 39W 34-inch (86cm) version if you want tighter coverage, or the 54W 46-inch (117cm) to run the full length. The T5 HO format produces around 4–5 UVI at 30–40cm, gives you far better gradient across the enclosure, and holds output much more reliably for 12 months. It's genuinely the best long-term investment for a dragon this age.

Wattage is less important than the actual surface temperature you're achieving — so the question is what the basking spot reads right now. For an adult bearded dragon, you want a surface temperature of 45–50°C on the basking platform itself (measured with a temperature gun, not an ambient thermometer). If your 100w bulb is hitting that, it's fine. If she's been slightly less active or eating less enthusiastically than she did at two or three years old, it's worth checking the basking surface is genuinely hot enough — dragons slow down metabolically if the basking spot is even 5°C cooler than optimal, and owners often assume it's just age. Do you have a laser thermometer to check the surface temp?

Yes — that's the single most impactful change you can make. The Arcadia T5 HO 12% gives your dragon consistent, measurable UVB across the enclosure for a full year, which is exactly what you want to protect her bones, immune system, and vitamin D3 synthesis as she gets older. Pick up the 54W 46-inch kit to run the full length of the enclosure and pair it with an Arcadia reflector if the fitting doesn't include one — it roughly doubles the usable UVI output. Get the temperature gun too, and once you have a surface reading you can decide whether the 100w basking bulb needs adjusting. You're in good shape for her age — this setup will see her through the next five years without issue.