Token passing data transfer mechanism for reservation based protocols is provided. A plurality of spring members extend into the plug aperture, and a plurality of plug contacts are mounted on respective ones of the spring members. To the light emitting elements are individually connected in parallel current bypass elements that are changed from a disconnected state where no current flows to a connected state where current flows when a predetermined voltage higher than that applied to the light emitting elements in an lighting state is applied thereto. The first and second narrow band filter is disposed on one surface of the first light to emitting panel and one surface of the second light emitting panel respectively. the inadvertent creation of a low-impedance path.