Reptile UVB Bulb Replacement Calculator
Calculate when to replace your reptile UVB bulb.
UVB output declines long before the bulb burns out — find your next replacement date.
UVB lighting is essential for most reptiles — it enables them to synthesize Vitamin D3, which is critical for calcium absorption and bone health. Without adequate UVB, reptiles develop metabolic bone disease (MBD), a painful and potentially fatal condition.
The invisible problem with UVB bulbs: A UVB bulb may still produce visible light while emitting little to no UVB radiation. The fluorescent phosphors that produce UVB degrade much faster than the filament. This means a bulb that looks perfectly bright may be providing zero UVB to your reptile.
Replacement intervals by bulb type:
| Bulb Type | Replace Every |
|---|---|
| T8 fluorescent (e.g. ReptiSun 5.0/10.0) | 6 months |
| T5 HO fluorescent (e.g. ReptiSun T5 HO) | 12 months |
| Compact/coil UVB bulbs | 6 months |
| Mercury vapor bulbs (MVB) | 12 months |
| LED UVB bulbs (newer tech) | 18–24 months |
Daily hours also matter: Running a bulb for 12 hours/day uses UVB capacity twice as fast as 6 hours/day. If you run your lights for more than 10 hours daily, reduce replacement intervals accordingly.
Signs of UVB bulb failure:
- Reptile basking more than usual (seeking more light)
- Reduced appetite or lethargy
- Soft jaw or limbs (early MBD)
- Use a Solarmeter 6.5 to measure actual UVB output — the gold standard
Daily schedule recommendations:
- Most species: 10–14 hours of UVB + basking per day
- Use a timer to keep the cycle consistent
- Replace bulbs on schedule even if they still produce visible light
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