UVB 5.0 vs 10.0: which one, and at what height

What 5.0 and 10.0 actually mean

They are output classes within a manufacturer's own range - roughly, the percentage of the lamp's emission in the UVB band. They are not a measurement of what reaches your animal, because that depends on distance, reflector and mesh. Treating 10.0 as "better" than 5.0 is the same category error as treating a 100 W bulb as better than a 50 W one without knowing the room.

The decision table

Why height decides it as much as species

Within a species, the output class you need is set by how far the lamp can sit from the basking surface. A 12% lamp needs about 11 inches of clearance through mesh to land UVI 4.0-4.5; a 14% needs 11 to 12 inches. In a tall enclosure where the basking platform cannot be raised closer to the lid, the stronger lamp buys you usable distance. In a shallower enclosure, the stronger lamp overshoots.

Which means the honest sequence is: measure your available distance from the lid to the top of the basking platform first, then pick the output class whose published distance fits inside it. The distance guide walks through this with the full figures.

Pick the 10.0 class if, pick the 5.0 class if

• 10.0 / 12-14% if you keep a normally pigmented bearded dragon, or any Ferguson Zone 3 animal, and your enclosure gives at least 11 inches between lid and basking platform.
• 5.0 / 6% if you keep a ball python or another Zone 2 animal, where the target is UVI 2.0-3.0 and a stronger lamp at the same distance simply overshoots.
• Neither if you keep a leopard gecko or crested gecko. Both are Zone 1 and need a ShadeDweller-class lamp; a 5.0 at gecko distances is still too much.