This reptile UVB lighting guide helps you find the correct UVB bulb strength, placement distance, and photoperiod for your reptile species. Select your species to get Ferguson zone classification, recommended bulb percentage, and daily lighting schedule.
Select Your Species
Ferguson Zone Reference
| Zone | UV Exposure | UVI Range | Bulb Recommendation |
|---|---|---|---|
| Zone 1 | Shade-dwelling / Crepuscular | 0–0.7 | T8 5.0 or low T5 5% |
| Zone 2 | Partial shade | 0.7–1.0 | T8 10.0 or T5 6% |
| Zone 3 | Open sun basker | 1.0–2.9 | T5 HO 10% or 12% |
| Zone 4 | High UV basker | 2.9–7.4+ | T5 HO 12–14% or MVB |
How to Set Up Reptile UVB Lighting
Reptile UVB lighting guide setup errors are one of the leading causes of preventable illness in captive reptiles. Metabolic Bone Disease (MBD) from vitamin D3 deficiency is almost entirely caused by inadequate UVB — and almost entirely preventable with proper lighting.
T5 HO vs T8 vs Compact UVB Bulbs
T5 HO (High Output) fluorescent tubes are the current recommended standard for diurnal reptiles. They produce stronger UVB at greater distances than T8 tubes. T8 bulbs work for lower Ferguson zone species kept close to the bulb. Compact coil UVB bulbs (the screw-in type) have inconsistent output and have been linked to eye damage — avoid them. Mercury vapor bulbs (MVBs) produce both heat and UVB from a single bulb, useful for basking species in large enclosures.
Placement Matters More Than Percentage
A 10% T5 HO bulb at 12 inches produces dramatically different UVI than the same bulb at 24 inches. Always consult the manufacturer's UVI data sheet for your specific bulb and set up accordingly. For best accuracy, use a Solarmeter 6.5 UV Index meter to measure UVI directly at the basking spot rather than relying on estimated distances.
Glass and Mesh Block UVB
Glass blocks nearly 100% of UVB. Mesh (screen tops) reduces UVB by 30–50% depending on mesh density. If your light fixture sits on a screen top, the UVB reaching your animal may be significantly lower than the bulb's rated output. Either move the bulb inside the enclosure or account for the mesh reduction by moving it closer.
FAQ
Is this reptile UVB guide free?
Yes, completely free with no signup required.
What UVB strength does a bearded dragon need?
Bearded dragons are Ferguson Zone 3 reptiles (high UV exposure). They need a 10–12% T5 HO UVB bulb (or equivalent) placed 12–18 inches from the basking spot, with a UVI of 2.9–7.4 in the basking zone. T5 HO 10% bulbs from Arcadia or Zoomed (ReptiSun 10.0) are the most commonly recommended. Replace the bulb every 6–12 months even if it still produces visible light — UVB output degrades before the bulb burns out.
Do snakes need UVB lighting?
Most snakes do not require UVB lighting for survival, but recent research suggests UVB improves overall health, natural behavior, immune function, and vitamin D3 levels even in species that are mostly crepuscular or fossorial. Ball pythons, corn snakes, and most colubrids do fine without UVB but benefit from a low-intensity source (2–5% T5 or 5.0 T8). Obligate UVB is not necessary for snakes unlike diurnal lizards.
How far should my UVB bulb be from my reptile?
Distance depends heavily on bulb type and percentage. T5 HO 10% bulbs provide adequate UVI at 12–18 inches. T8 bulbs are weaker and should be 8–12 inches. Compact/coil UVB bulbs are not recommended — they have inconsistent output and can cause photo-keratoconjunctivitis (eye damage). Always check the manufacturer's Ferguson zone data for your specific bulb and adjust placement to achieve the target UVI for your species.
How often should I replace UVB bulbs?
T5 HO bulbs should be replaced every 6–12 months (most manufacturers say 12 months, but output degrades significantly before burnout). T8 bulbs every 6 months. Mercury vapor bulbs every 6–12 months. The bulb will continue to produce visible light long after UVB output has dropped to inadequate levels. A Solarmeter 6.5 UVI meter is the only reliable way to verify actual UVB output.