I want to implement 4 lighting maps(diffuse, specular, normal and emission) for each fragment and I could implement this by using a texture array or a texture atlas(each lighting map will have different texture coords). I don't want to make mandatory all the 4 lighting maps for all textures so I would need to use some default lightning maps. The problem is that in both cases I would need to duplicate the default maps into the texture array/texture atlas. This makes me think to use a different texture per lighting map but isn't this too much for a batch renderer?(since a GPU has generally 32 texture slots)