With good quality CFB UVBs ( Arcadia , Zoo Med , Exo Terra ) the spectrum is good .
The typical configuration using a DOME style reflector produces a tightly focused beam of UVA & UVB and here in lies (IMO) the biggest issue if the CFB is a good one.
Working out if your dragon is getting adequate UVA & UVB from the CFB is as easy as looking at a flux vs distance chart , noting if the globe is naked or in a reflector dome ( or hood ) , and if there is any screening between the globe and the dragon ( the mesh used in typical commercial tanks' lids is quite fine so will block in the order of 40% of the UV , more or less negating the benefit of the reflector hood . dome ).
Distance chart that will give you a bit of a guide
aim for basking spot UVB flux 180-200 microW / sq.cm.
In a smaller tank , CFB of at least 25W 10% UVB is FINE , but you will get better spread and coverage if you mount under the lid in a NANO-STYLE hood like this :
https://jurassicjungle.com.au/products/exoterranaturalnanoterrariumcompactlighthood