- Open Finder
- Navigate to: Users/YourUser/NameHere/Library/Preferences
- Warning: Be mindful of changing the wrong file or touching incorrect settings in this folder. This could go wrong!
- Open: com.apple.bezelservice.plist
- Change kHWMin to have a value of: 1
- Close and save
You have now adjusted the minimum light the light sensor needs to activate the back-light on the keyboard.
Note: Only valid for Macbook Pros, normal Macbooks do not contain keyboard back-lights.