BTW: I have a little problem. I have an arena positioned inside a sphere. The problem is the lighting of the sphere looks very odd. The bottom is completely lit and so is a strip down one of the sides.
Maybe the light is discarded before reaching the sphere. If you based you work on the fps-example, this is very likely to happen, because the example modifies the discard distance. Have a look at Config.lightDiscardDistance...maybe it helps. Keep in mind that performance will decrease the higher this value is set. How much depends on your polycount.
About the render-to-texture: If you are using OpenGL, this is not really possible. It could be done if the rendering to a texture happens only once or at least very seldom, but for frequent updates, there's no way ATM.