Brightness Test
Test display brightness range and sensors
Bottom linePush brightness to maximum—it should be very bright with no dim or yellowed zones. Then enable Automatically adjust brightness in System Settings > Display and cover the camera area: the screen should dim within 2–3 seconds and recover in the light. No response points to a faulty ambient light sensor or a replaced display.
Test Maximum Brightness
Press F2 or use Control Center to set brightness to maximum. Screen should be very bright
Test Auto-Brightness
System Settings > Displays > Enable 'Automatically adjust brightness'. Cover the camera area (where the sensor is)
Verify Sensor Response
Move between bright and dark environments. Brightness should adjust smoothly within 2-3 seconds
Tip: If auto-brightness doesn't respond, the ambient light sensor may be faulty or the screen may have been replaced.