Clouding

Poor workmanship not necessarily the cause

Unevenness on the translucent plastic layer in front of the backlight is the cause. Usually, lower-priced devices or entry-level models are affected more often. Over time, the intensity can increase due to ongoing overheating and expansion of the layer. 

This can have various reasons and does not have to be directly related with the TV itself. Possible causes can therefore be diverse. Starting with a generally too high room temperature over a longer period of time. Regular direct sunlight on the screen can also lead to this problem. Especially in poorly insulated attic flats during summer, the heat level, which is usually considerable anyway, can contribute to this.

Wall mounting can also be a problem

It is also possible due to a flat wall mounting of the TV and the resulting heat build-up on the back of the housing. In combination with a heated wall, the effect could be further increased. Strong heat radiation, caused for example by shelf lamps nearby, can also be a possible factor. This is why, at the first sign, you should check whether one or perhaps even more of the above possibilities apply.