The Peace of Freysdal by Michael Richards

Freysdal is a peculiar place for more reasons than one. Besides manufacturing radiant items for non-Light-Twisters, it's also the only place in Thadren where thralls and freemen work side by side. Jaren knows that he's no more than a small piece in the effort to overthrow Thralldom, but he's comfortable with that role. That comfort is shattered, though, when he learns that he can control radiant energy. Now, instead working to be reunited with his sisters, Jaren must resist the burden that drives Light-Twisters to cruelty and survive an abusive radiance instructor long enough to figure out who's trying to kill Freysdal's founder. The stress ramps up with growing rumors of an impending attack on Freysdal, and Jaren must decide whether he's willing to give up the Peace of Freysdal and become the Sword that defends it.