The structure is:
R = diffuse(Nx,Ny,Nz,S)
The output R is defined with Lambert's Law by R = cos(psi) where psi is the angle between the surface normal and light source.
If you have a surface on the (x,y) plan, the normal vector is [Nx,Ny,Nz] = [0,0,1].
S = [Theta Phi] is the direction vector of the light source in spherical coordinates (in degrees).
For example
S = [10 45];
R = diffuse(0,0,1,S)
You can also define S in the (x,y,z) coordinates. That would give, to have the same output:
S = [sind(45)*cosd(10) sind(45)*sind(10) cosd(45)];
R = diffuse(0,0,1,S)
