from the online manual "The Lighting Engine" :

"Normal engines support only 8 dynamic light sources because that's the limit of today's 3D hardware. The A7 engine however contains a light manager that can render a theoretically unlimited number of dynamic light sources at the same time. Before rendering a particular mesh or object its 8 closest light sources are automatically activated and all other light sources are switched off. This way the 3D hardware limit is still kept, despite hundreds of light sources can be visible at the same time."



Maybe the problem lies in the limitation of 8 light sources per mesh. I have to admit that i'm not really sure what a mesh is.
But if your sewer complex is one big model (object) only 8 lights can affect it...
So if that's the problem you should split up your level models into smaller parts i think, so that each part is lighted by max 8 lights - but as i said, just a guess