☀️ Bearded Dragon UVB Distance Calculator
Find the right basking distance for your UVB bulb to hit a safe UV Index (UVI).
Distance is measured from the bulb (or top of mesh) to the highest point of the basking spot — not the floor of the tank.
Sources: Arcadia Reptile official lamp specifications, Zoo Med product specifications, ReptiFiles UVI guidance. This tool is provided for general educational purposes and does not constitute veterinary advice.
What Happens If UVB Is Too Close to a Bearded Dragon?
Mounting UVB too close can push the UV Index at the basking spot well above the safe range, which has been linked to eye and skin irritation in reptiles kept too close to their bulb. This is exactly why manufacturers publish minimum distances — Arcadia, for example, states its T5 HO bulbs with a reflector should be no closer than 12 inches to the basking spot, regardless of enclosure height.
What Happens If UVB Is Too Far Away?
If the bulb is mounted beyond its effective range, your dragon may be getting little to no usable UVB at all — even though the light still looks bright and “on.” Over time, insufficient UVB exposure prevents proper vitamin D3 synthesis, which is the underlying cause of Metabolic Bone Disease (MBD), one of the most common and preventable health problems in pet bearded dragons.
How Far Should a Bearded Dragon’s UVB Bulb Be?
The correct distance depends entirely on which bulb you’re using — there’s no single number that applies to every setup. As a quick reference:
| Bulb Type | Manufacturer-Sourced Distance |
|---|---|
| T5 HO 10–12% (Arcadia Desert / Zoo Med 10.0 T5 HO) | 12″ minimum (Arcadia) |
| T5 HO 14% (Arcadia Dragon Lamp) | ~15″ for UVI 6.0 (Arcadia) |
| T8 5.0 | ~12″ effective range (Zoo Med) |
| T8 10.0 | ~20″ effective range / recommended placement (Zoo Med) |
| Compact/coil UVB | No reliable generic chart — check product packaging |
| Mercury Vapor Bulb (MVB) | Varies by brand/wattage — check product chart |
Use the calculator above to get a specific recommendation based on your exact bulb, life stage, and whether you’re mounting over mesh.
Is a T5 HO or T8 Bulb Better for UVB Distance?
T5 HO bulbs generally project usable UVB farther and more evenly than T8 bulbs of the same strength rating. That said, Zoo Med’s own specs show their T8 10.0 reaching a comparable 20-inch range to many T5 setups — the bigger practical difference is that T5 HO fixtures tend to spread UVB more evenly across a wider basking area, which matters more in larger, modern 4ft+ enclosures.
How Do I Know If My Bearded Dragon’s UVB Setup Is Actually Correct?
Distance charts — including the ones on this page — are starting points, not guarantees, because real UVB output depends on your specific bulb, reflector, fixture, and how long it’s been running. The only way to know your dragon’s actual basking-spot UV Index is to measure it directly with a UV Index meter, such as a Solarmeter 6.5. For bearded dragons, most sources recommend a basking-spot UVI in the 3.0–6.0 range, tapering to near 0 at the cool end of the enclosure.
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