Thanks for your answers.

Frenchy Pilou (PILOU) : I think that "modo" is the default option for vertex normal style for lwo export (but I tried with lightwave, and the result is the same).

steve (STEVE_HOME) : To "Flip" objects I need to know which one I need to flip, so I need to export first, then check which objets are hidden, then flip those objets, then export once again.
So I think I will add a thickness.

I've used cinema 4D to display normal, and now I'm now almost sure that my problem come from normals :