Well. At least its good to know, that i can spend my exp on something else.
But sad, that good spell in avatar shop is useless due to that limit. Since darkness isnt a thing you can freely drop out from that game.
Actually, real problem is that you just cant stop that permalight after you buy it, if you want to use usual aegis with dark cloak. So maybe good way around balance will be ability to turn it on/off with some special spell with big mana cost? Like 300-500mana(lets not forget about quad nocasters

). So it will be hard to abuse it. But we will be able to choose what we want now - permanent light that cant be cloaked, or no light at current moment.