Rand didn't have that effect on Trollocs, Fades, and such, right? He still had to use the OP to destroy them.

It would make sense that any BA or Dark Ashaman have some kind of link to the DO (to protect Taim from the Taint, among other things). This link would protect them from Rand's new ability. We've seen the link between forsaken and Shaitan, to give them power over shadowspawn. We've also SH's special mark that makes shadowspawn not attack his "children." It's so terribly unlikely that Rand will be able to stop Moridin or Demandred through "Light Power." It would just be too easy.

My guess is that normal humans who are Dark do not receive any of the DO's protections, but evil channelers get at least something. The bad folks at the BT shouldn't be defeated by Rand's presence or glare or "Light Power."