In relation to lights...

Any lights positioned within my scene apart from ambient lights, do not show up in the final render.
Maya 6, using only polygons with low uv spans.

My scene in the main perspective window looks great! There are several different types of lights, all carefully placed in space and not inside any objects (!) These are producing subtle effects which don't show at all in the final render - just a dull, flattened scene is revealed... What could be the problem?

Thanks for any advice.