We are going to force everybody to live according to "light-givernence" rules.
So who's in who's out ?
Force, really!
Every human likes the idea of freedom and freewill. You can't be thinking of something good and the first way to preach it is by forceful means and admittance. The very idea of force leads to rebellion, maybe not immediate but, its sure to come around.
If your light government is good, You show it. They say, light can't be hidden by darkness. You let your light shown so bright such that, its noticed all around and the people in darkness would see reasons to come to the light and be free from the bonds that held them in the dark side of life.
Again, don't think you can have everyone or dispense darkness completely, it's a part of the world, evil is in the heart of men and would continue to persist in a few but, that doesn't mean you shouldn't do the most you can.