Do bearded dragons need UVB?

Why the answer is unambiguous here

A bearded dragon is a diurnal, open-sun basking desert lizard. In the wild it thermoregulates by exposing itself to high UV during the day, which places it at the upper end of Ferguson Zone 3 with individuals occasionally reaching Zone 4 at midday. UVB drives vitamin D3 synthesis, which is what allows dietary calcium to be used. Without it, calcium supplementation does far less than the label implies, and metabolic bone disease is the long-term outcome.

The number, and how to hit it

The published target is UVI 4.0-4.5 at the basking surface, with the optimal gradient running from 0 at the far cool end up to that figure at the basking site. Two routes to it:

Those figures assume roughly a 45% mesh block. If you do not own a meter, the published advice is to add 1 to 3 inches to account for your particular dragon's height, and to make the basking area the highest point in the enclosure and the closest point to the lamp.

Three rules that go with it

• Tube length. Roughly half the enclosure length, on the same side as the heat lamps: 22 inches for a 4 ft enclosure, 34 inches for a 6 ft.
• No shield. UVB is blocked by glass and plastic, so a fixture with a cover over the lamp provides none at all.
• Replace at 12 months. Output declines well before visible light does.

And the lighting that is not UVB

Beyond UVB and basking heat, the guidance recommends bright approximately 6500 K illumination for optimal wellbeing, covering 75 to 100% of the enclosure length - which may mean more than one lamp. It is the easiest improvement to a dragon setup that nobody talks about, and it visibly changes activity levels.

The full setup, with heat and substrate, is on the bearded dragon lighting page, and the enclosure that has to accommodate it is covered in the sizing guide.