Apple Macintosh Performa 570 series - Manual (Page 39)

Using the screen control buttons on your computer
You can adjust the level of light and dark on the screen of your built-in
monitor by using the screen control buttons on your computer (marked with
the ¸ icon).
m Press the button at the top to lighten your screen.
m Press the button at the bottom to darken your screen.
¸
Screen
control buttons
31 Expanding Your Computer and Using Special Features