Render triangles with normals, and DX does all the lighting calulations for you. What happens if you try to render without color or normals in the vertex? Does DX calculate the normal for the verts at render time? Oddball Software
http://zap.to/oddball

>>>Direct3D applications do not need to specify face normals; the system calculates them automatically when they are needed. The system uses face normals in the flat shading mode. In the Gouraud shading mode, Direct3D uses the vertex normal. It also uses the vertex normal for controlling lighting and texturing effects. <<<

no - because the vertex normal vector is arbitary.