I'm afraid this is more or less considered normal with this sort of panel technology. You may be able to reduce the effect using these methods:
1- Enable the Ambient light sensor
2- Change the picture mode to "Cinema"
3- Play around with the picture settings if you don't like the look of "Cinema" mode as the visibility of such lines depends mainly on the brightness and colours.
One thing to note is that cranking up the brightness and turning off the lights is considered a worst case scenario for this kind of phenomenon. One of the reasons TV manufacturers consider this to be normal is how hard it is to spot in "normal viewing conditions" = moderate/auto brightness(sensor) + moderate lighting.
Win_88
