How to disable Macbook Pro internal display when using external monitors

Turning the brightness down as suggested above turns the monitor off on my MacBook Pro - mid 2014 model. Keeping the lid open allows better dissipation of heat and keeps the fan noise to a minimum so this is my preferred mode of working.

You should be able to close the lid and use an USB mouse/keyboard to awaken the computer to only use the external display.

The interesting thing here, is that you use an USB-graphcis adapter too. That software may confuse this process.

I would suggest just using the native graphics ports to begin with and see if you can make it work, and then add the USB-adapter.

I use a very naive solution on a Macbook Air mid-2012: instead of using clamshell mode (closing the lid), I just press the brighness down button until the lowest level. For my surprise, the lowest level turns off the internal display. I don't know if this works for others models, but it works well for me.

There's a tool that allows you to disable internal display: https://github.com/Eun/DisableMonitor.

I've been using it with success in the same scenario.

Disclaimer: I'm not a maintainer, so I fear I won't be able to provide support in case of any problems. Please use github issues.

On 10.6 an earlier, the internal display stayed disabled even after opening the lid. There's a firmware variable that restores that behavior:

sudo nvram boot-args="iog=0x0"

I don't know if it would help in this case though. You don't have to reboot when changing display configurations.