As you can see in this image the diffuse shading is working correctly in some places but in other places such as the the bottom of the sphere you can see the squares/triangles of the mesh. Any idea what would be causing this? Let me know if you need anymore information related to code. I can upload my normals calculations and shader effect if required. EDIT: Here's a link to the shader I'm using http://pastebin.com/gymVc7CP Link to normals calculations: http://pastebin.com/KnMGdzHP Seems to be an issue with edge lighting. Can't seem to see where I'm going wrong with the normals calculations though.