We have recently put a new UV strip into Lucifer's vivarium since the old one needed replacing but since we have done this a thick stripe at the base of his tail has appeared which is a lighter and duller colour than the rest of his scales. He isn't shedding yet so I am not sure what is it? Any suggestions please?

if you could post pictures up that might help a little bit

This sounds like its about to shead
What reptile is it? how old is it?

He's going to shed soon.
When they get uneven time under the UV lights and heating, they can shed like this. It's nothing bad, but it might take some time before the rest of the body sheds too. Don't worry too much about this. If he has weird behaviors too, post them because he could be sick but I highly doubt it. My bearded dragon Diablo is going through this right now with all of his limbs besides his back. When it happened with old beardie Vector I was afraid but when I saw it was gone on him and there was skin on his bedding, I knew he was just shedding.