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.?

  • Have you tried an antiglare film such as radtech.us/products/clearcal-displays The glossy screens do transmit light more efficiently and diffuse the colours less; I suspect also it would have been an environmental disaster to acid etch all the glass; maybe a film would help?
    – Colin
    Commented Oct 27, 2013 at 22:39

8 Answers 8


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


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.)


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.


Your problem actually exists whether the iMac is on or off.

The glare from sun (or other light sources) will not go away when you turn off your iMac, since the glass will still reflect the external light source. I find it to be worse when the power is off.

You'll need to focus on old world solutions: fabric draping, turning the angle of the iMac to some degree that reflects the light away from you (remember angle of incidence equals angle of reflection) .


You can purchase an antiglare film to the iMac. I googled https://www.google.com/#q=antiglare+film+for+iMac and found tons of products for the iMac. Though this option might slightly reduce the quality of your displace, you would be gaining significant screen real estate for the low low cost of ~$30.


You could purchase a mini-mac and move the current iMac elsewhere.


You can swipe over to the accessories desktop and dim the display. In mavericks, the grey grid is pretty dark on its own and you can just remove the accessories. In yosemite, setting your desktop to a solid black background, swiping over, removing all accessories, and dimming the display makes it pretty dark.


I removed the glass screen from my late 2009 iMac. It made the computer useful. It was not the LCD itself that caused the worst glare reflection, it was the glass window in front. I can be removed. Once removed, the computer does not look so good. You can buy a panel without the glass (maybe still available) or you can cover up the edges with tape. My solution did not look good, but the screen did and made the computer quite usable. Keep the glass in case you need to move it or want the LCD protected.


Unfortunally not possible, you can use an app to reduce the brightness however turning it off, i think not!

you know what lets give this one thing a shot though Display Preference Pane -> Arrangement -> Drag the menu bar to the monitor your want as primary! then try Ctrl+shift+eject it MIGHT work, i dont think so though!

OR try either turning the brightness way down, or use brightness slider on the mac App Store this however wont "stop stressing your graphics card"

  • 3
    This is annoying. Nobody at Apple ever though about this? I found the SHADES program. It Shades the iMac's monitor to black and with a normal daylight, you can't see that the screen is slightly lit. It even works when the same screen is shared with both screens (video copy). The CTRL+SHIFT+EJECT closes both screens... Anyway. Thanks for your help.
    – nicolas
    Commented Mar 15, 2013 at 16:41
  • hm okey, did you look at the brightness slider app?
    – Macmaniman
    Commented Mar 15, 2013 at 19:29
  • 1
    @nicolas Would you kindly provide a link to SHADES ?
    – Simon
    Commented Oct 11, 2013 at 16:59

Just turn the brightness all the way down

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