I would like to know how to turn off the retina display when the computer is connected to a HDTV by HDMI.
It would be good for watching films or vidéos.
The easiest way is establish the connection to the TV, then turn the display all the way down with the brightness keys.
With an external keyboard and pointing device, you could run your rMBP in clamshell mode - http://support.apple.com/kb/HT3131.
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