What country are you in if I may ask? The link Thea gave is good, though the information there is quite dated. There used to be lights listed as "BL", which were dark fluorescent tubes that would give off UVA &/or UVB, but very little visible light. I can't remember the last time I saw one, they seemed to have vanished years ago when all the newer UVB lights started to come out.
If that is what it is, it would be allright for UVB. You would be better off getting a more modern bulb if at all possible though. And, though it appears "black", you don't want to use it at night. It is producing "daytime" type light, and you should use it along with a bright white basking light.
Do you know what brand it is, or who makes/sells it? I am curious, I thought those were completely out of production.