"not only would it be unscary, but the framerates would drop to zero"
Just because a pixel's color becomes black doesn't mean that it no longer exists and is therefore not rendered. That's like saying black really isn't a color.
I had joked in another thread here that our framerates should skyrocket if that were the case... because with the lighting it seemed like I was only actually seeing 100 (albeit gorgeous) polygons at any one time.