Adjust keyboard backlighting
If your portable Mac has a backlit keyboard, you can adjust the level of backlighting.
Turn backlighting off: Press the decrease keyboard brightness key until the keyboard is no longer lighted.
Turn backlighting on: Press the increase keyboard brightness key until the keyboard is bright enough for your needs.
Automatically adjust backlighting in low light: Choose Apple menu > System Preferences, click Keyboard, click Keyboard, then select “Adjust keyboard brightness in low light.”
Automatically turn backlighting off after a period of inactivity: Choose Apple menu > System Preferences, click Keyboard, click Keyboard, select “Turn keyboard backlight off after [time period] of inactivity,” then choose a time from the pop-up menu.
The light sensors are located in your computer’s speaker grilles; make sure the grilles are not covered when you use your Mac in low light conditions.