I don't think it's a backlight issue. For one thing, the center of the half circle isnt directly in the corner, it starts a little ways towards the center. It's hard to describe, the rightmost edge of the circle starts about where the minimize button is on windows. Plus, this wasnt there until a a month or so after I got it the monitor. If it was a problem with backlighting, I would think it would have been there from the start.