A refrigerator includes a cabinet forming a storage space, a main door that opens and closes the storage space while defining an opening part that is in communication with the storage space, a sub-door mounted to the main door and configured to open and close the opening part, the sub-door including a panel assembly for allowing selective viewing of an inside of the opening part, the injection port is provided at a lower side of the sub-door to direct an insulating foaming solution to a space in the sub-door, a detection device for detecting an operation of a user, a lighting unit inside the refrigerator that turns on based on user operation to allow selective viewing of the inner side of the opening part, and a display unit inside the refrigerator at a position corresponding to the panel.