My laptop is a DELL 3521 with dual graphic cards, which usually cause some problems, and I have switched off the AMD Radeon card.
Now, when I want to turn the brightness down by dragging the brightness bar in the "Brightness and lock settings" and I close the window, nothing changes, and when I open "Brightness and Lock Settings" again, the brightness bar turn back to its previous state!
So, is it something is the system or I did some kind of mistake?