Thanks for the bug report. It sounds like Xorg's (fake) brightness setting is being applied repeatedly. I would generally recommend avoiding that feature because it works by degrading color quality (tweaking the gamma ramps / color profile). I recommend using your monitor's brightness setting instead. Otherwise...
Please try uninstalling the "brightness-controller app" you mention and reboot, then tell us if that fixes the problem. If it doesn't then we're probably only left with Xorg or MATE to blame. ** Package changed: xorg (Ubuntu) => xorg-server (Ubuntu) ** Changed in: xorg-server (Ubuntu) Importance: Undecided => Low ** Changed in: xorg-server (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to xorg in Ubuntu. https://bugs.launchpad.net/bugs/1960569 Title: Screen goes dim To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/1960569/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp