This is exactly what my screen looks like, with light leak across the bottom and up the sides. It is my third screen. All 9C85 screens. Every one has displayed the same problem. My current screen is week 47. I had an idea of waiting 2-3 months then start the process all over again, hopefully by then it should calm down. Especially with the renewed LG contract that Apple have just agreed to. The only possible issue with that is Apple coming back to me at that point and claiming "the screen is showing expected results" and not replacing it.
At the present time i think its pointless exchanging or replacing.