If you wish to get some details; check the site linked here. Pull up older posts. Surf the site with patience. http://electronicshelponline.blogspot.com/
Line, faults & possible causes to LCD screen are given with illustrations. You can get an idea about the fault to an extent.
Probably not a back light problem. What happens if you activate the screen test display?
It depends on standard factory settings by each manufacturer of the TV. However, while you may keep the brightness, contrast and color settings as per standard settings of the TV (generally they are 50%), the LED backlight may be kept to the bearest minimum and depending on your viewing pleasure. This will enable long life to your LED Panel. If DCR is available, turn it off and manually reduce the backlight setting to the bearest minimum.
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