When working at your Mac, there may be times when you would like to simply shut off the monitor without interrupting your work. For example, if you are downloading files or in the middle of processing a large amount of data that will take hours to complete, or if you are simply playing music and do not want to view anything on your display, then you might like to blank out the display.

The Energy Saver system preferences can be used to set the display to sleep after a specified time frame, but not on-demand (click image for larger view).
OS X supports putting a display to sleep after a period of inactivity, which you can set in the Energy Saver system preferences; however, in addition it supports several options for immediately putting your display to sleep:
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The Terminal
Open the Terminal and run the following command:
pmset displaysleepnow
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The keyboard
Press the following keys on your keyboard, depending on whether or not your Mac has an eject key or a power button:
Shift-Control-Eject
Shift-Control-PowerNote that for third-party keyboards, you might need to find the key mapped to the “Eject” function, and press that. This may require you hold the Fn key. You will also have to hold the Fn key if your Mac’s F-keys are set to be standard function keys instead of Apple’s special features. This setting is available in the Keyboard system preferences.
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Hot corners
You can hold various modifier keys (in this case the Shift and Command keys) when setting a hot corner, in order to require these be pressed for the specified action (click image for larger view).
Click the “Hot Corners…” button in the Desktop & Screen Saver system preferences, and then choose “Put Display to Sleep” as the function for a specified hot corner. Then move your mouse to this corner and the display will sleep.
With these options, you can quickly put your Mac’s display to sleep while keeping the computer active in the background. Keep in mind that if you have the system set to require a password upon waking from sleep or screen saver deactivation (set in the General section of the Security & Privacy system preferences), then you will need to authenticate when waking your display back up. Otherwise, upon pressing a keyboard or mouse button you will be right back at your desktop.
I like to use this free app, Caffeine:
https://itunes.apple.com/ca/app/caffeine/id411246225?mt=12
Caffeine prevents your Mac from going to sleep. This article covers the options for putting your Mac’s display asleep while keeping your Mac active and running in the background.
Ah, true. I use a Mac mini with an external display. With Caffeine I can keep the mini running and then turn the display off.
The keyboard shortcut, Shift-Command-Eject does not work on my new iMac with a wireless Apple keyboard. I have to use a hot corner for this function.
is there a way to keep a macbook pro from going to sleep when I power off my 27″ external display connected via hdmi cable, with the MBP in a henge dock? My energy saver setting are set so the MBP should still be awake for an hour.
Yeah, I’m having this issue as well. Putting the display to sleep used to be independent of sleep, now it seems to put the computer to sleep after a minute or so – which kills my open processes.
Thank you very much
mac sucks