macOS Sierra: Adjust your display’s brightness
If the images on your display are too light or too dark, you can adjust the display’s brightness.
Use the brightness function keys
If the screen seems too light or too dark, you can adjust your display’s brightness.
Use the brightness keys: Press the increase brightness key or the decrease brightness key (or use the Control Strip).
Automatically adjust brightness
If your Mac has an ambient light sensor, choose Apple menu > System Preferences, click Displays, then click Display.
Then select “Automatically adjust brightness.”
If you don’t see the “Automatically adjust brightness” checkbox, you can manually adjust the brightness.
Manually adjust brightness
Choose Apple menu > System Preferences, click Displays, then click Display.
Drag the Brightness slider to adjust the brightness of your display.
Depending on the type of display connected to your Mac, you may also see a Contrast slider that you can use to adjust the display’s contrast.
You cannot adjust the brightness of some older Apple displays. In OS X v10.10 and later, the Brightness slider may no longer appear in the Display pane of Displays preferences.
For specific information about the brightness of your display, check the documentation that came with your display.