How to Adjust Brightness Manually On an External Display To do so, click the Apple menu and select “System Preferences.” Click the “Displays” icon in the System Preferences window and adjust the “Brightness” slider to your desired level. In this case–or if you just prefer using your mouse–you can adjust brightness in OS X, too.

If you’re using a different keyboard with your Mac, you may find the brightness keys in a slightly different place, or you may not see any brightness keys at all. If these keys are set up to function as standard F-keys instead of special action keys, you’ll need to press and hold the Fn key as you tap them. You’ll see an on-screen overlay appear, showing you the precise brightness level. Just press the keys to decrease and increase your brightness. The F14 and F15 keys will do the same–look for the keys with sun logos on them. On a Mac desktop PC, look at the top-right corner of your keyboard.

The F1 and F2 keys will decrease and increase your brightness.

On a MacBook, look at the top-left corner of your keyboard.

Adjust brightness mac shortcut