How to disable Macbook Pro's display with the lid open

locomocojoe · Oct 17, 2014

Does anyone know how to disable the MacBook Pro's screen while connected to an external monitor on Mac OS X 10.10 Yosemite?

The previous methods using the command line trick found in the link below no longer works on the new os.

Yet Another Way to Turn Off Internal LCD Display of MacBook Pro With Lid Open | OSXDaily

And dimming the screen is not the same as turning it off, as the GPU still has to send two signals to the internal display and external monitors. This in turn generates more heat and uses more resources and drains the battery quicker.

Slydude · Oct 17, 2014

If you have an external keyboard and monitor attached closing the lid puts the computer in "clamshell" mode. Some users have concerns about this but it has been used for many years with few, if any, problems. See this thread for example

pigoo3 · Oct 17, 2014

locomocojoe said:
And dimming the screen is not the same as turning it off, as the GPU still has to send two signals to the internal display and external monitors. This in turn generates more heat and uses more resources and drains the battery quicker.

First. This may be true…but it's not a problem (from a heat/temperature perspective).

Secondly. Why would you be operating your MacBook Pro on battery power with an external display attached?? :Confused:

- Nick

chscag · Oct 17, 2014

Also as Apple makes very clear in their KB article regarding clam shell mode; it does not work when you're on battery power.

pigoo3 · Oct 17, 2014

chscag said:
Also as Apple makes very clear in their KB article regarding clam shell mode; it does not work when you're on battery power.

Thanks for mentioning this Charlie.

I was really scratching my head why someone would be operating a notebook computer with an external monitor attached while on battery power. AND…if it was even possible.

- Nick

locomocojoe · Oct 17, 2014

pigoo3 said:
First. This may be true…but it's not a problem (from a heat/temperature perspective).

Secondly. Why would you be operating your MacBook Pro on battery power with an external display attached??

- Nick

Well if you leave it plugged in all the time as I do, sometimes it's good to power cycle your battery every so often. So therefore, you unplug the power cord--right?

chscag · Oct 17, 2014

locomocojoe said:
Well if you leave it plugged in all the time as I do, sometimes it's good to power cycle your battery every so often. So therefore, you unplug the power cord--right?

That's right and immediately your external monitor will go black. There's no way an external monitor can pull power from your MacBook Pro when it's on battery. At least not without doing damage to the logic board circuitry.

pigoo3 · Oct 17, 2014

locomocojoe said:
Well if you leave it plugged in all the time as I do, sometimes it's good to power cycle your battery every so often. So therefore, you unplug the power cord--right?

Yes...I do the same thing.

My MacBook Pro is also plugged in 99% of the time...and I also cycle the battery roughly once/month.

But this once/month battery cycling does not necessitate (or in any way justify or explain) why the need for an alternate way to clamshell mode is needed. There just is no problem running a MacBook Pro in clamshell mode.

And like "chscag" mentioned. If you do this (run the MacBook Pro on battery power) with an external monitor attached...the external monitor will go black.

So the explanation above (post #1) why it is a good thing to not have internal & external video hardware operating at the same time (external monitor attached) because it will drain the battery quickly...does not hold water. Since you cannot have an operational external monitor attached to a MacBook Pro while on battery power (thus the external video hardware is not operating)...and thus there is no extra battery drain while on battery power due to the external monitor.

- Nick

locomocojoe · Oct 18, 2014

pigoo3 said:
Yes...I do the same thing. My MacBook Pro is also plugged in 99% of the time...and I also cycle the battery roughly once/month.

But this once/month battery cycling does not necessitate (or in any way justify or explain) why the need for an alternate way to clamshell mode is needed. There just is no problem running a MacBook Pro in clamshell mode.

And like "chscag" mentioned. If you do this (run the MacBook Pro on battery power) with an external monitor attached...the external monitor will go black.

So the explanation above (post #1) why it is a good thing to not have internal & external video hardware operating at the same time (external monitor attached) because it will drain the battery quickly...does not hold water. Since you cannot have an operational external monitor attached to a MacBook Pro while on battery power (thus the external video hardware is not operating)...and thus there is no extra battery drain while on battery power due to the external monitor.

- Nick

I'm not sure where you're getting the idea that the external monitor goes black on battery only, mine does not do this (lid open as I don't run on clam shell mode). I have 2 external monitors running on battery only it's fine and the screen does not go black and can go for 5+ hrs like this. Maybe it's the Fall Late 2013 models, which I have, but I am not seeing what you're talking about.

Anyhow, this is way off topic of the original thread. Cheers on your feedback and endorsement on clam shell mode.

chscag · Oct 18, 2014

By going black we do not mean the monitor loses power - (monitor works off AC) what we're saying is that it loses its video signal (goes black).

How to disable Macbook Pro's display with the lid open

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