Yes --- you need correct lighting and placement along w/ correct basking temps taken w/ a digital probe thermometer -- MVB what brand and bulb and what is the distance you have it at? How long have you had the MVB -- most do not give out enough UVB and needs to be supplemented w/ a long tube type
MVBs send out too narrow a field of light. You want your UVB covering two-thirds of the enclosure for bearded dragons, not just hitting in one concentrated area.
Which MVB brand are you using? Some have been emissions than others. MVB lights are
good in the fact that they are great for a heat source & UVB together. As suggested, a lot of
the times, it is beneficial to couple a tube UVB with them also for a better balance & coverage
of UVB.
What are the temperatures in the tank?