Rt is correct - when using a fluorescent strip UVB its best if its unobstructed - while larger mesh is better than very fine mesh, its still going to filter some of it.

You can cut a slit in the mesh, or mount the bulb inside the cage
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1.1 Bearded Dragons
2.2 Leopard Geckos
1.0 Uromastyx (Mali)
1.1 Corn snakes
0.1 Mexican Black Kingsnake
1.0 Bairds Ratsnake
1.0 Rosy Boa
1.1 Green Anoles
1.1 House Geckos
0.0.2 Flying Geckos
0.0.1 Red Eye Tree Frog