Related (maybe) to "Strange Glowing Buildings"

Surface normals are definitely a hack, but a worthwhile one in many cases. Radiance does it's level best to deal with perturbed normals in the ambient calculation and elsewhere. Results aren't always perfect, but hey -- it's Radiance, not Renderman!

To remove surface normal interpolation from a .OBJ file (converted with obj2rad), apply the -f option. To eliminate them from 3DS files when you used 3ds2mgf, you can use the little-known mgfilt program after 3ds2mgf and before mgf2rad (there really should be a -f option added to mgf2rad, I suppose). Here's an example:

  3ds2mgf building.3ds
  mgfilt '#,c,cct,cone,cmix,cspec,cxy,cyl,ed,f,ies,ir,m,o,p,prism,rd,ring,rs,sides,sph,td,torus,ts,v,xf,fh' building.mgf | mgf2rad > building.rad

A nasty command just to remove surface normals, but it beats writing a script (for most people).