My TV is automatically darker, although the eco mode is disabled?

I recently bought a Samsung Smart TV. (SAMSUNG UE49NU7179UXZG)
Everything works fine except that my brightness goes down automatically, but not in Tv mode; i.e. Only with netflix, youtube, etc.

Picture mode: Standard
Backlight: 42
Brightness: 0
Contrast: 50
Sharpness: 10
Color: 25
Hue (G / R): 0
Apply picture settings: All sources
Digital recycle: car
Auto Motion Plus Settings: Auto
Contrast improvement: Low
Movie mode: Off
Color: standard
Gamma: BT.1886
- BT.1886: 0
RGB mode only: Off
Color Space Settings: Native

General → Eco Solution → Everything disabled

As I said in TV mode, everything fits, but on Netflix, Youtube, etc., the picture is automatically darker.

Maybe if you look Netflix automatically another picture setting is selected switch everything on car or on Manuel

Have I always when a black picture comes, for example When opening yt, nf, etc., he darkens the black much further down and that is in the movie just like that

This is a setting which is not found in the eco-setting. But in the menu under "environment sensor" shows up…

Here the green dot must be removed.

If this is already done and no improvement then it may be that the device is running on "Business Mode" and every few minutes automatically reset the image…

Or it may even be the night mode on YouTube enabled