Fix Monitors Not Falling Asleep when Using the nVidia Drivers on Linux Mint Xfce

tldr; xset dpms 600 0 0 replace 600 with time in seconds to sleep your monitors.

This is for when your power manager can blank the displays but they don’t fall asleep, leaving the back light on.

First, run xset q and look for DPMS (Energy Star):if you see something like Standby: 0 Suspend: 0 Off: 0 we are on the right track.

Test that this standby mode works, run xset dpms force standby. Hopefully your monitors went to sleep, and wiggling the mouse woke them back up. If not, double check your mouse didn’t move. If your monitors are stuck blank, try either switching to a terminal with Ctrl + Alt + F1 (then possibly restarting your window manager there), using the key command that restarts your display manager, or restart the machine. Oops sorry!

If that did work, you can now use xset dpms X Y Z replacing X with the time in seconds to “standby” (make the monitors go to sleep), typically 600 (10 minutes), Y to “suspend”, typically 0, which is disabled, and Z for “Off”, typically 0. As far as I understand, the later modes were designed for CRTs and don’t typically work or do anything on other displays[Citation Needed].

Example: xset dpms 600 0 0

If you want to make sure this is working and don’t want to wait, just use smaller number xset dpms 10 0 0 now every 10 seconds your monitors are trying to fall asleep.

Tested on the MacPro 1,1 running Linux Mint 18.3 Xfce 64-bit
Notes: Xfce’s power manager had the issue, the command fixed it. On Mate, this xset command actually made the monitors fall asleep while displaying video. Mate’s “Power Management Preferences” worked fine for sleeping correctly with Put display to sleep when inactive for 1 minute.