Run the check
Use a dark room, moderate brightness, and a full black pattern.
Move your head gently while keeping the display and exposure unchanged.
Repeat from the normal seating position and photograph only as a personal record.
Read the result
A patch that shifts with angle differs from one fixed at the same edge position.
Limits and next step
Camera exposure exaggerates black-screen brightness; this is a visual comparison.
Repeat the check after changing one setting or connection. Keep a record of what changed before deciding whether the device needs service.