I think this isn't possible, but I just want to check this:
Is it possible to create a face in opengl that has two normals?
So: I want the inside and outside of some cilinder to be drawn, but I want the lights to do as expected and not calculate it for the normal given. I was trying to do this with backface culling off, so I would have both faces, but the light was wrongly calculated of course. Is this possible, or do I have to draw an inside and an outside? So draw twice?