A UVB tube can keep glowing long after it has stopped doing the one job it was bought for, which is why replacing it on a calendar matters more than checking whether it still lights up.

This is a T5 Very High Output fluorescent tube using Exo Terra's Sunergy phosphor blend, engineered in Germany, putting out 7% UVB — aligned with Ferguson Zone 2, the mesophotic zone, for reptiles that bask only occasionally in direct sunlight. It's 12in long and fits standard T5 fixtures, including the Exo Terra T5 Terrarium Top.

• T5 Very High Output (VHO) fluorescent tube
• Sunergy phosphor blend, engineered in Germany
• 7% UVB output — Ferguson Zone 2 / mesophotic
• 12in length
• Fits standard T5 fixtures and the Exo Terra T5 Terrarium Top
• For reptiles, amphibians and invertebrates only

On when to replace it. Exo Terra's own warning is that a T5 tube can still look perfectly bright long after its UVB output has dropped below a useful level — so replacing it by a schedule rather than by eye is the only way to know your animal is actually getting UVB rather than just light. No specific replacement interval is stated on this listing; check the manufacturer's guidance for this bulb specifically.

Who it's for: keepers of reptiles classed as occasional or partial baskers — species in Ferguson Zone 2 — who need moderate UVB rather than the highest output on the shelf.