@marcikaa78 that is an issue with one of the diffuser sheets on the inside of your LCD panel. COuld be wrinkled from hot or stained. The only way to fix this would be by tearing down your panel. It is possible that either cleaning or replacing the diffuser sheet would get rid of those lines. It is a lot of work and requires the complete teardown. If it does not bother you to much, I would recommend to leave it as is. If you have never taken a panel apart, it'll be a bit tricky. No, not impossible but just tricky :-). If you do wan to take it apart, let us know and we can try to walk you through the procedure step by step.