[vtkusers] illumination model in vtk

[sha1 at doc.ic.ac.uk]

I want to set illumination model. Just to explain : "Many people confuse Phong
shading with Phong illumination. Phong shading simply refers to process of
interpolating the normal across a surface for shading on an individual pixel
 basis. At each pixel, you can do whatever illumination you prefer. Or, you could
 use Phong illumination at each vertex, and use Gouraud shading across that
 surface." .
In vtk , to change shading you would write :-
vtkactor->GetProperty->SetInterpolationToGouraud
You , can play with illumination by setting ambient, diffuse and specular
properties of the actor . But can you change illumination model that is being
used to color vertices. And how to play with parameters of the illumination
model ? I am sure vtk is using illumination model , I want to have detailed
understanding of that. 

 
 Regards,

 Hassan Amin