Bearded dragons are Ferguson Zone 3 animals — among the highest UV-requiring reptiles kept in captivity. In the wild, they bask in direct Australian sun for extended periods each day, accumulating UV exposure at levels most other reptile species never encounter. In captivity, UVB lighting replicates this. Getting it wrong doesn’t cause an immediate visible problem; metabolic bone disease develops slowly and silently, often showing up weeks or months after the UVB shortfall started.
This comparison covers the two choices that matter most — T5 vs T8, and Arcadia vs Zoo Med — plus exact distances, replacement schedule, and the evidence on compact/coil bulbs.
Quick Answer — UVB Bulb for Bearded Dragons
Use a T5 HO linear tube — either Arcadia T5 HO 12% Desert or Zoo Med ReptiSun T5 HO 10.0. Both achieve the required UVI of 4.0–4.5 at the basking zone. Mount approximately 11” / 27cm above the basking surface through mesh, or 16–17” / 40.5–42cm without mesh. Replace every 12 months regardless of whether the bulb still looks bright.
Ferguson Zone 3 — Why the UVI Target Is What It Is
The Ferguson Zone system, developed by Gary Ferguson and colleagues, classifies reptiles by their natural UV exposure in the wild, from Zone 1 (crepuscular, minimal UV) to Zone 4 (full-sun, extreme UV). Bearded dragons are Zone 3 — high-UV baskers that in their native habitat regularly encounter UVI readings of 4.0–6.0 at the basking site. VCA Animal Hospitals confirm that UVB lighting is essential for this species in captivity.
In captivity, a bearded dragon’s vitamin D3 synthesis is calibrated to this level. Lighting that works for a Zone 1 species will leave a bearded dragon in progressive vitamin D3 deficit. The UVI target of 4.0–4.5 at the basking zone is the floor, not an aspirational target. This is why T5 HO bulbs are standard — they reach this UVI at a safe, practical distance in typical enclosures. T8 bulbs often can’t, particularly through mesh tops in standard-sized enclosures. For the full D3 synthesis mechanism, see the bearded dragon UVB guide.
T5 HO vs T8 — The Comparison
| Feature | T5 HO | T8 |
|---|---|---|
| UVB output | High | Low-medium |
| Effective range | Greater distance | Short range |
| Replacement interval | 12 months | 6 months |
| Performance through mesh | Adequate with correct distance | Often inadequate |
| Cost over 2 years | One replacement | Two replacements per year |
| Verdict | ✅ Recommended for standard setups | ⚠️ Only viable inside enclosure at close range |
Standard mesh tops block approximately 45% of UVB output. A T8 bulb mounted above mesh in a 4x2x2 or larger enclosure frequently can’t deliver UVI 4.0 at the basking surface even at minimum recommended distance. The result is months of apparent UVB exposure while the dragon receives well below the required dose.
T8 can work in one specific scenario: mounted inside the enclosure (bypassing the mesh entirely) in a short tank where the basking surface is genuinely close to the bulb. This is an edge case rather than a practical recommendation for most modern setups.
Arcadia vs Zoo Med — Head to Head
This is the question most keepers settle on after deciding on T5 HO. The straightforward answer: at their respective recommended distances, both deliver UVI 4.0–4.5. This isn’t a choice between a stronger and a weaker product — it’s a practical choice based on regional availability, fixture preference, and whatever comes with the best reflector kit in your market.
| Metric | Arcadia T5 HO 12% Desert | Zoo Med T5 HO ReptiSun 10.0 |
|---|---|---|
| UVB strength | 12% | 10% |
| Distance through mesh | 11” / 27cm | 11” / 27cm |
| Distance (no mesh) | 16–17” / 40.5–42cm | 16–17” / 40.5–42cm |
| Replacement interval | 12 months | 12 months |
| Strongest availability | UK and EU | US; available globally |
| Kit option | Arcadia ProT5 (fixture + reflector included) | Various hood kits |
| Verdict | ✅ Best for UK/EU | ✅ Best for US; solid global alternative |
On 12% vs 10%: The higher percentage means Arcadia 12% can achieve the UVI target from a slightly greater distance — useful in enclosures where the basking area sits deeper than typical. At the distances in the table above, both bulbs hit the same UVI target. “12%” doesn’t mean “more UV delivered in use” — it means “achieves the target at a greater working distance.”
Arcadia Dragon 14%: For very tall enclosures where the basking surface is unusually far from the ceiling. Distance: mesh 11–12” / 28–30cm; no mesh 17–18” / 43–45cm. Not for standard 4x2x2 setups.
Reptile Systems 12%: Also approved by ReptiFiles. Calibrate with a Solarmeter 6.5 — exact distance guidelines aren’t available due to different output characteristics.
Distance Guide — Exact Measurements
Measure from the basking surface (the top of your dragon’s back at basking height) to the centre of the UVB tube.
| Bulb | Mesh Present | Mounting Distance |
|---|---|---|
| Arcadia T5 HO 12% | Yes | 11” / 27cm |
| Arcadia T5 HO 12% | No | 16–17” / 40.5–42cm |
| Arcadia Dragon 14% | Yes | 11–12” / 28–30cm |
| Arcadia Dragon 14% | No | 17–18” / 43–45cm |
| Zoo Med ReptiSun 10.0 | Yes | 11” / 27cm |
| Zoo Med ReptiSun 10.0 | No | 16–17” / 40.5–42cm |
Source: ReptiFiles UVB distance table, based on approximately 45% UVB reduction through standard mesh.
A few important setup notes: The basking surface should be the highest point in the enclosure — close to both the UVB tube and the heat lamps. Don’t place glass or plastic between the bulb and the enclosure interior; UVB is blocked entirely by glass and most plastics, making a “protected” bulb completely useless. And if you don’t have a Solarmeter 6.5 to measure actual UVI, ReptiFiles recommends adding 1–3” to the mesh-distance numbers above to account for your dragon’s height at the basking surface.
Bulb Length — What Size to Buy
| Enclosure Length | Target Bulb Length | Approximate Wattage |
|---|---|---|
| 4 ft / 120cm | 22” | 24W |
| 6 ft / 180cm | 34” | 39W |
| Larger | Covering warm side + basking zone | 54W or dual rig |
The tube should cover the basking zone and warm side — not the entire enclosure length. This creates a UV gradient: high UVI at the basking site, decreasing toward the cool end. The gradient matters because it allows your dragon to self-regulate UV exposure, moving out of intense UV when it’s had enough.
Compact and Coil UVB Bulbs — The Evidence
Do not use compact or coil UVB bulbs for bearded dragons.
A 2017 study at Wageningen University (Netherlands) tested bearded dragons under compact fluorescent UVB bulbs designed for reptile use. After 120 days, plasma vitamin D3 levels in the test animals were barely detectable, and all showed early-stage MBD. These were bulbs sold specifically for reptile UV use — not generic lighting products.
The reason compact bulbs fail: they emit UVB in a small hotspot roughly 5–10cm in diameter with no usable gradient, and their UV output drops approximately 50% within the first 3–4 months of use. A compact bulb that’s been in service for four months is likely producing negligible UVB while emitting normal visible light.
Many starter kits sold in pet shops still include compact coil UVB bulbs. If your setup came with one, replacing it with a T5 HO linear tube is the single most impactful upgrade you can make.
A brief note on LED UVB bulbs: the technology is developing, but experts including Frances Baines, Sarina Wunderlich, and Thomas Griffiths have concluded that current LED UVB products are not safe for reptile use, regardless of manufacturer claims. T5 HO fluorescent remains the standard until this changes.
Replacement Schedule — The Invisible Failure
UVB fluorescent bulbs degrade through phosphor breakdown, not through filament failure. The coating that produces UV emissions deteriorates over time — and this process doesn’t affect visible light output. A T5 HO bulb that is 14 months old may look perfectly bright while producing near-zero UVB.
| Bulb Type | Replacement Interval |
|---|---|
| T5 HO fluorescent | Every 12 months |
| T8 fluorescent | Every 6 months |
| Mercury vapor | Every 6–12 months (manufacturer spec) |
| Compact/coil | Not recommended — replace with T5 HO |
The best practice is simple: write the installation date on a piece of tape applied to the fixture when you install the bulb. Replace it on the anniversary. Set a calendar reminder. Without a Solarmeter, the schedule is the only indicator you have.
The Solarmeter 6.5 is the only device currently validated for accurate reptile UVI measurement. For keepers who want certainty rather than schedule-based replacement, it pays for itself in the information it provides — and catches UVB failures that a visual inspection never would.
Morph Exception — Reduced Pigmentation Dragons
Most bearded dragon morphs follow the standard UVI 4.0–4.5 target. Hypomelanistic, translucent, and silkback dragons have reduced pigmentation and potentially higher UV sensitivity. For these morphs, the maximum recommended UVI at the basking site is 3.0, not 4.0–4.5.
Achieve lower UVI by either using a lower-output bulb or increasing the mounting distance beyond the standard table above. If you’re uncertain about your dragon’s morph classification, ask the breeder or consult a reptile vet.
Summary
| Decision | Recommendation |
|---|---|
| Bulb format | T5 HO linear fluorescent tube |
| Brand (UK/EU) | Arcadia T5 HO 12% Desert |
| Brand (US/global) | Zoo Med ReptiSun T5 HO 10.0 |
| UVI target | 4.0–4.5 at basking surface |
| Distance (mesh) | 11” / 27cm |
| Distance (no mesh) | 16–17” / 40.5–42cm |
| Bulb length | ~1/2 enclosure length |
| Replacement | Every 12 months |
| Compact/coil bulbs | Do not use |
| Morph exception | Max UVI 3.0 for hypo/translucent/silkback |
For UVB hours and lighting schedule, see the bearded dragon lighting schedule. For the full UVB and vitamin D3 mechanism, see the bearded dragon UVB guide.
Frequently Asked Questions
Does this article explain the science behind why bearded dragons need UVB?
No. This article compares specific bulb products — brand, format, mounting distances, and performance. For the Ferguson Zone classification, D3 synthesis mechanism, UVI target rationale, and the consequence of UVB deficiency, see Bearded Dragon UVB Guide.
Does this comparison cover how many hours the UVB light should run per day?
Photoperiod — the daily and seasonal on/off schedule — is separate from bulb selection. See Bearded Dragon Lighting Schedule for the full schedule including seasonal adjustment and brumation reduction.
Does this article cover Mercury Vapor Bulbs that combine heat and UVB in one fixture?
Yes — MVBs are covered as a third format option. Note that MVBs replace both the UVB tube and the basking heat lamp. For the basking heat lamp as a separate fixture (the standard approach), see Bearded Dragon Basking Light Guide.
Do the mounting distances in this comparison apply to reduced-pigmentation morphs?
No. Hypomelanistic, translucent, and silkback dragons require a maximum UVI of 3.0 at the basking site, compared to the standard 4.0–4.5. To achieve this with the bulbs listed here, increase mounting distance beyond the standard table — and verify with a Solarmeter 6.5.
Does this comparison article apply to setups using outdoor natural sunlight?
No. This article covers indoor artificial UVB only. Outdoor enclosure considerations — including natural sunlight benefits, shade requirements, and UV overexposure risk — are covered in Bearded Dragon Outdoor Enclosure.
This article is for educational purposes only. Incorrect UVB setup is a common cause of metabolic bone disease in captive bearded dragons. If your dragon shows signs of MBD — soft jaw, limb bowing, tremors, or chronic lethargy — consult a reptile-experienced veterinarian promptly.