HOW TO DIM A LAPTOP SCREEN

First step is to locate the two sun-looking icons with a + or - sign in front of it; this could be anywhere on the keyboard. Then locate you Fn key which is usually found on the lowest row of keys. Next you need to push and hold the Fn key while you repeatedly tap the -sun button. You can use this method to also increase the brightness by just replacing the -sun key with the +sun key.

Hope this helped!