Build ligths per objects

It is very annoying to lose all information about build lights after unreal crash. The program shuts down when building is 98% after 2 days waiting and everything is over. The information of the calculated lightmaps should be automatically stored in some folder to be able to retrieve them.
Another solution could be “build ligths per objects” … imagine that you could calculate the illumination of objects that were not calculated after the crash. I don’t know if I’m explaining this correctly. Sorry for my English.

People have requested this for ages; may never happen…