Hi there! I guess only per pixel lighting will fix this issue. By default acknex uses vertex lightning as far as I know. So the best way to fix that, is to use shaders (to write it by yourself, cause I can't really recall a 'ready-to-use' solution for that Edit: I guess those bumpmapping shaders from AUM or free resource page are having per pixel lightning).
Edit: also, face-separation might help. I remember something about this from Superku, will try to find now.
Edit2: I couldn't find it.. so here I've made some screen shots to show what I meant by face-separation:
1 - this is a simple 'smooth' box created in MED, it will have some lightning issues (same as on your screenshot).
2 - select one of it's sides (f.e. the top as on this picture) and press COPY (near by the OPEN, SAVE etc)
3 - after copying it, remove the side (press delete)
4 - press PASTE button which is right next to COPY, and you'll get separated top side of the box
5 - continue with the rest 5 sides, and you'll get a box with separated faces
This will help to get more or less proper lightning, but per pixel lightning shader is MUST have too (combined with this tips).
Edit3: also, you can see differences between vertex lightning (only looks good on more or less high polygon models/surfaces) and per pixel lightning on this videos Vertex Lighting BDX Devlog #2 - Per-Pixel Lighting