I want to be able to 'put the display to sleep' on one of my two monitors when it isn't needed, so it doesn't distract me or use unnecessary power.
Ideally, the display would be asleep, but the OS would remain in dual-monitor mode, so I could still have a variety of windows open in the sleeping monitor's display space, which would mean I wouldn't have to keep switching between single- and dual-monitor modes.
That said, I'd also consider a solution that made it easy to toggle between single- and dual-monitor modes without navigating several system menus.
Best Answer
Press Windows + P - you will be prompted to choose your display mode from single, extend, etc and so can be used to disable your secondary monitor.
I see you wanted to keep your open windows; this still keeps them open, but it does bring them all to one display if you enable single monitor mode. However at least this approach will let you shut down the second glowing distraction when it is not in use.