Anyway, I am willing to bet it has to do with the inverter transformers that drive the backlight. There are two in that TV (see image below).
I expect one of them (the one that drives the backlight on the left-hand side of the screen) is failing or has burned out completely. Are you experienced with repairing electronics? If so, it is as simple as finding a replacement part (should be easy to find by googling the part number on the transformer), desoldering the old one, and soldering a new one in. I did this on my Samsung a year or two ago and it worked like a charm after the repair.