When I set up some sort of light for example a PointLight and put it on the left side of a model. For some models the left side gets brighter but for other models the right side gets brighter, although the light is on the left side? Same with other light Sources.
Perhaps the other models are inside-out: their mesh normals point inward instead of outward.
Also, example code would be useful to make sure there isn’t something else going on (like sharing a Vector3f for dir that changes later, etc.)
TangentBinormalGenerator can help visualize the normals of your mesh.
genNormalLines(Mesh mesh, float scale) will return a new (unlit) mesh representing the normal vectors at each vertex of the mesh passed in.
if your mesh is not centered at origin, you may want to align the returned “normals” mesh appropriately.