As such it may be a similar failure (not the same!) as you see at http://www.youtube.com/watch?v=oE6K4xBVweA
Notice the result of that repair and then imagine if some back lighting has failed.
As this is not user serviceable you would get repair estimates.
My LED TV Samsung UE46D8000YS start to have one level darker picture on the top of screen around 25cm narrow horizontally through all screen, Can you please advice. All connections are checked and found OK. Last firmware 029. Thank you.