good normals but no lighting when i display the meshes

I compute my normals and i multiply it by the tranformation matrix of my .3ds file. When i compare the results with the normals’ values of the .ase file of the same meshes, i have same results but the meshes aren’t lighted, and they are when the normals are a little different with a negative value for example(ex: -0.24 in the .ase and 0.24 with my own values)
I compute vector ab and ac.
Do you see what can be the error ? is it an error of checking the .ase file’s values ?


Be aware that in the ase/3ds files, the z and y axis are swapped, and you must corect this first. Then be sure that we’ve enable the OpenGL lighting and the specific light that afects the object.