I don't know about other holy paladins but I generally don't use Divine Light a whole lot during fights. Despite having a lot of spirit, it is still a mana sink to be casting it over and over. On Megaera for example, I used it only 10 times. This is complicated in your case by the fact that you don't have the 4 set pve. This will help you a lot in generating Holy Power and you can almost fill up 2/3 of your time by casting instant casts like EF or HS. You can of course use DL on anyone who's about to die quickly but I would try my best to DL only on beaconed members. You can even macro your beacon to it to help you although I am personally hesitant to do things like this.