Yep, I'm aware of that but I don't have the best solution yet - Changing the black rgb value is not an option so it will probably be something with the edge lines.

yes, I was thinking about letting the user choosing the color of the borders (white for dark part or "invert color" of the color of part to cover all the case....)

Can you put more spots at different place ? maybe not if you'e aware of the pb.

Thanks for the response anyway.

The difference between the very dark areas and clear ones does not actually come from a spot lamp but an image (processed) used as an environment map. So whatever I choose there will be darker areas. If I increase the white values (more light), the other colours don't look good - overexposed. Hence my preference for a tweak with edges. However I would need to solve the case of decorated parts.