If you have a Mac with a Thunderbolt 3 (USB-C) or USB-C port, you can connect it to an external display using a Thunderbolt 3 (USB-C) cable or a USB-C to DisplayPort cable. You can also use a DisplayPort cable to connect a Mini DisplayPort display, such as the Apple LED Cinema Display.
You can use an external display as your primary display, extend your desktop, or work in mirroring mode with your Mac. If you’re using an Apple Thunderbolt Display or LED Cinema Display, you can also use it as a power source for your Mac.
To turn off your Mac’s display when connected to an external display, do the following:
- Connect your Mac to the external display.
- Open System Preferences, then click Displays.
- Click the Arrangement tab.
- In the Arrangement tab, uncheck the “Mirror Displays” checkbox.
- Click the Options button, then select “Built-in Display Off”.
- Close System Preferences.
Your Mac’s display will turn off when you disconnect it from the external display.