Interesting idea. In early playtesting we had considered making Light better against Dark. Many of the playtesters were against having that because it gave the Priestess a huge advantage over the Warlock. Of course, we could have made some counterbalances.
Instead we chose to make Light more powerful against Nonliving, which gives Light a little more flexibility and less narrow of focus. Light can now be effectively used against all Incorporeal from all schools (Incorporeal are always Nonliving), all Golems (like the Iron Golem), and will still be deadly against Nonliving Dark creatures like the coming Necromancers Undead forces.