I'm making a small game in Unity, and some models are displaying very ugly shading. The shading usually looks funky along the edges between triangles. I'm pretty new to working in 3D; I bet this is an artifact of vertex lighting, but I'm not sure, and I'm not sure how to fix it.
Here you can see the worst example of this problem:
Low-quality lightmapping is visible in that shot, but I'm asking about the visible bands and weird shapes visible on the surface of the orange mesh in the foreground. The mesh was built and UV-mapped in Blender, and is using a standard bumped diffuse shader. There is a light behind and above the camera; all other lights in the scene are pretty far away. What am I doing wrong, and how can I do better?
EDIT: Below is the wireframe for this model in Blender.