VertexNormals->{n1, n2, ...} specifies that vertex i should have effective normal ni for purposes of shading by simulated lighting.
The ni are vectors of the form {vx, vy, vz}. Only the directions of these vectors ever matter; the vectors are in effect automatically normalized to unit length.
VertexNormals->None specifies that no explicit vertex normals are being given, and normal directions should be deduced from the actual coordinates specified for vertices. For point and line-like primitives, no shading based on simulated lighting should be done.
EXAMPLES
Basic Examples 
Scope 