I have Windows 10 Pro, and it is just combined with another CPU (Dell Optiplex 7020).

I tried using the buttons on the side of the screen. On the screen, something came up, to adjust the visual properties. I read the word "Brightness". There was a little line which went up and down from 0 to 100. Even when I press the buttons, and the line goes up and down, the brightness of the screen did not change, very much.

I also tried adjusting thru the Display Settings of Windows 10 Pro. I saw the Night settings, but the screen just becomes more orange, rather than becoming darker. 

Does anyone know how to decrease the screen brightness? Thank you!