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I'm using an external monitor for my 2015 Macbook Air. I don't want this thing to overheat, so i open the lid so heat can escape upward. However, that puts everything back in 2-display mode, using more graphics card / RAM to drive that second screen, which works against my goals.

I can press CMD+option+eject (on my apple bluetooth keyboard) to turn off both screens, while the computer keeps running. How can i do this to just one screen?

  • You could unplug the second screen when not in use. Either physically, or via Preferences. – Didier Apr 2 at 16:31
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Lid-closed operation is a fully supported feature of MacBooks running macOS. Their thermal management system won't let them overheat. The black plastic "clutch barrel" (the center section of the screen hinge) is shaped so it doesn't block the vents even if fully closed. If you suspect you're hitting thermal throttling of your CPU or GPU, or if your fans are running higher than you'd like, then make sure you're not thermally insulating the bottom of your MacBook (don't use a case that fits too tightly, don't set it down on fabric).

If you still want it to run in lid-closed mode with the lid open, put a magnet on the "lid closed" hall-effect sensor (it's usually to the left of the bottom row of the keyboard, if I recall correctly).

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  • The sensor is typically actually on the front edge of the machine. If you take a paperclip and hold it along the top edge of the screen, you'll find the built-in magnet in a heartbeat. Then the sensor is just at the corresponding spot on the palmrest. Also, for others reading this, the 16-inch MacBook Pro (2019) has a lid-angle sensor, so this magnet trick might not work with that model. – Bob Apr 3 at 0:15
  • Does the Apple OS not have an option to simply show the screen on the second monitor? Windows can do that, and it's a quickly accessible option. I'm surprised Apple doesn't, unless I'm misunderstanding... – BruceWayne Apr 3 at 1:02
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    @BruceWayne OP isn't having any problem using the external display. He wants a way to turn off the built-in display while he uses the external display, without having to close the lid of the laptop. He doesn't want to just turn off the backlight of the internal display, he wants to ensure no GPU resources or other resources are used for calculating any graphics for, or sending any signal to, the internal display. – Spiff Apr 3 at 3:11

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