You reach into the refrigerator for a cold drink. The door stands open, and the interior light floods the shelves, illuminating bottles, fruits, and leftovers clearly.
With the item in hand, you swing the door toward the frame. As long as a gap remains—even a thin one—the light stays on, and the contents remain visible from outside.
The door continues closing. It nears the frame completely.
At the precise moment the edge meets the frame and the rubber seal compresses fully around all sides, the fridge door seals.
Before this, light glows steadily, and slight pressure can reopen the door easily. Right after, the light clicks off abruptly, plunging the interior into darkness, and the door holds shut without effort.
The fridge has crossed the line from open and lit to sealed and dark.