OpenGL: throw out triangles/quads in a certain direction.

Question

Context:

I'm doing shadow mapping. When rendering the scene from the eye's point of view, I'd like to throw out certain triangles/quads ... in particular, elements of the following property:

L = light position C = center of scene

V = L - C

I want to throw out the elements whose normal N satisfy dot_product(V, N) = close to 0.

[The reason for throwing these out is that they get weird values in the depth map when rendering from the light's perspective; this then results in problems / artifacts when rendering shadows from the eye's view and looking into the depth buffer from the light's view.]