Refrigerator and control method thereof

A refrigerator comprising:

• a cabinet configured to form a storage space;
• a door configured to open and close the cabinet, and rotatably connected to the cabinet by a hinge, the door having a door frame with an opening which is in communication with the storage space;
• a panel assembly provided at the opening and configured to allow an inside of the refrigerator to be seen through the panel assembly from an outside of the refrigerator, the panel assembly comprising:
• a front panel,
• an insulation panel spaced apart from a rear surface of the front panel, and
• a spacer bar provided between the front panel and the insulation panel, wherein an insulation space is defined between the front panel and the insulation panel;
• a knock detection device disposed to be in close contact with the panel assembly, and configured to detect a user's knocking operation on the panel assembly;
• and
• a lighting unit provided inside the refrigerator and configured to be turned on based on a signal of the knock detection device in a state in which the door is closed to allow the inside of the refrigerator to be seen through the panel assembly from the outside of the refrigerator,
• wherein the knock detection device is provided outside the insulation space.