How Often to Replace a Leopard Gecko's UVB Bulb
| T5 HO UVB tube | Replace ~every 12 months |
| Compact/coil UVB bulbs | Replace ~every 6 months |
| Visible light is not a reliable indicator | UV output degrades first |
The bulb keeps working, the UV doesn't
A fluorescent UVB bulb's visible light output stays roughly constant for a long time, which is exactly why relying on 'it still lights up' as a replacement signal is unreliable — the UV-B wavelength output declines well before the visible light does.
Typical replacement window
Most manufacturers and keepers replace a T5 HO UVB tube every 12 months of regular use (roughly 10–12 hours a day), regardless of whether it still looks functional. Compact/coil UVB bulbs typically need replacing even more often, around 6 months, which is part of why T5 HO tubes are generally preferred.
Tracking it
Writing the install date directly on the fixture or enclosure, or setting a recurring reminder, is a simple way to avoid running an old, UV-depleted bulb for months past its useful life without noticing.
Why it matters
A depleted bulb gives a false sense of security — the enclosure looks lit correctly, but the gecko may be getting little of the D3-synthesis benefit UVB is meant to provide.
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A single adult leopard gecko needs a 20-gallon long tank as an absolute minimum, with a 36x18 in (40-gallon breeder) footprint now considered the recommended standard — plus a secure lid, an under-tank heater on a thermostat, a thermal gradient, at least three hides, and a shallow water dish.
Set up in this order: substrate, then heat source wired through a thermostat, then hides and water dish, then decor — and run the whole enclosure for at least 24–48 hours to confirm stable temperatures before your gecko moves in.
Hatchlings can start in a 10-gallon tank or tub, juveniles do well in 20 gallons, and adults need a 20-gallon long as an absolute minimum — with 36x18 in (40-gallon breeder) now the widely recommended standard, not just an upgrade.
Heat a leopard gecko enclosure with an under-tank heater and/or overhead heat source (halogen or deep heat projector) wired through a thermostat — a thermostat is mandatory, not optional, and heat rocks should never be used.
Leopard geckos can survive without UVB using dietary D3 supplementation, but current husbandry guidance now recommends low-level UVB (roughly 2–6% T5) as best practice — it improves D3 synthesis, bone density, and natural behavior, and views on it have shifted significantly from older nocturnal-species advice.
Keep ambient humidity around 30–40% across most of the enclosure, with a dedicated humid hide raised to roughly 70–80% to support smooth, complete sheds.