in this pic we're rendering a non smoothed box,
but we're passing face normals to lux (masquerading as vertex normals)
in this scenario we're actually having 3 vertices at each point with they're own vertex normals.
so in total 24 vertices (4 per face) are exported. (and during export each quad is cut into 2 triangles!
this is'nt very optimal, so in case of non smooth objects, just drop them, lux can calculate these for you. (and only export the 8 original vertices)
(if it's really necessary like with portals or transmitters, you can use this scenario)
so i'll sum it up:
non-smooth: export faces, vertices
smooth: export faces, vertices and vertexnormals
non-smooth but need to control direction of faces?: export faces, vertices and facenormals as vertexnormals, but triple your vertices and each vertex normal belonging to a face is the same face normal.
check the luxblend export mesh function, it's python too and very readable and it explains it all