Just to pile on - yes, they absolutely need UVB light. If you don't use the combo light like alter-echo mentioned, you would want to make sure the rays from the basking light and rays from the UVB light overlap a little. All of this aids in their physical development, ability to process foods and absorb calcium.

UVB should be replaced every 6 months regardless of if the light goes out or not.

There is a great bearded dragon forum here: https://beardeddragonforum.com/ if you want a more in depth discussion and understanding of the husbandry requirements for beardies.