Does relight work in a coop/multiplayer save game? my friend and I have both download relight into to the map we are using, but the join and download mods buttons are greyed out when I try to join him.
If you both play a mod map that has relight packaged into it you should be able to play together. Right now I don't think it will let you play vanilla maps, I could be wrong tho. I'm trying to get a standalone version released today so hopefully your issue will be resolved even if you have no luck yourself