UN55C8000 ...the "UN" is Samsung's method of labeling the TV as an LED TV.
PN58C8000 ...the "PN" is for Plasma.
Generally speaking, LED TVs have awful viewing angles: if you stand a few feet off center the colors look terrible, and everything goes to hell. This particular LED TV from Samsung exhibits such a flaw. And IMO, most LED TVs just "aren't quite there yet." If you want to buy a new TV, def get the Plasma version, since they're cheaper (and in this case bigger) and have excellent PQ.