Turn off iMac main screen while working on external

I have an external display on my iMac and I would like to work only on the external display and turn off/disable the iMac one, just like the "clamshell mode" on a Macbook for example. It works with Windows in Bootcamp, but not in the Mac's partition. The iMac's display is too shiny and it gives me headaches when I work while the sun is shining.

How can I turn off the iMac's screen so it won't stress my graphic card, display etc.?

Solution 1:

I succeeded by using switchresx. Terminal command

brew cask install switchresx

then, open System Preferences, SwitchResX

Click icon, setup a display set with a disabled primary display, setup hotkey (ctrl-opt-f1 for me), save&close SwitchResX

Then, if you want to use single external display mode, press the hotkey et voilà

Solution 2:

Old school solution: Buy a yard of light-blocking fabric at your local fabric store. Hang it over the monitor (or tape it at the top of the screen if you're concerned about heat buildup.) This at least gets the job done. (Note: Make sure you turn on screen mirroring in Display Preferences so you don't lose your mouse pointer off the edge of the screen you're using.)

Solution 3:

i have the same problem, i don't know how its not possible to turn off the iMac monitor while still keeping on the external display. i got both apps, shades and slider, use them together and it goes completely black, i guess this will have to do for now.

i used the shades app first to lower the brightness to about 15-20 percent. then on the external monitor i used to the slider app icon on top of the screen to lower the iMac monitor the rest of the way to pitch black.