How to Quickly Enter Clamshell Mode with an External Display in Mac OS X

Keeping a portable Mac turned on while the lid remains closed is commonly referred to as clamshell mode. This basically docks the MacBook Air/Pro/etc and allows the GPU to power an external display only which can help performance of some games and graphics intensive tasks. There are several ways to enter into clamshell but this is probably the fastest for those who use an external keyboard or mouse with a MacBook.

1. Connect the external display and an external keyboard or mouse to the MacBook Pro or Air
2. Close the lid of the MacBook
3. With the lid closed, click the mouse button or hit a keyboard key
4. The MacBook will awake and the external display will turn on, becoming the primary display

This should work in all versions of OS X without any issues. Be aware that running a MacBook with the lid closed reduces the ability for the Mac to dissipate heat through the rear fan ports and the keyboard which could theoretically lead to overheating, making clamshell best used in well ventilated areas or with a Mac that’s placed in something like a TwelveSouth BookArc, which is what’s holding the MacBook in the image above.

If you open the lid at this point the displays will flicker blue and both screens will turn on, that can be prevented if you’d rather keep the internal display turned off, or you can go with it and set the primary display to tell the Mac which screen to use for the menu bar, Dock, and where windows will default to open to. 

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