Inconsistent lighting with Unity 5

I have a randomly generated cave system. The idea is to have a ship of some kind fly around in it and use light to see what’s going on, but the lighting I’m using isn’t consistent. I use a spot light and it does its job when hitting surfaces below, but not up.

I’ve attached a picture to show it. In the top you can see that the light affects the walls of the cave, but in the picture below, when the light is facing upwards, it isn’t shown on the walls. The wall is one mesh, by the way.

I think there are two major questions which would help with this:

  1. Is the light built-in, or is it a custom light being passed into the shaders?

and…

  1. Is the environment itself randomly generated? If so, are the vertex normals facing the correct directions?

Based on the images, my best guess would be that the normals on the environment are all facing “up” (as opposed to “out”). Therefore, light would only shine on the surfaces if they’re facing upward and the light is facing downward.