lugs 461 in which are provided respectively notches 462 at the closed end of the cylindrical hollow member 46 is an opening 466 in the periphery of the cylindrical hollow member 46 are two diametrically opposing openings 465 and two diametricallt opposite engaging holes 463 each engaging hole 463 has an angled end for engagement there are a spring 47 and a circular plate 48 in the hollow member 46 the circular plate 48 has two opposite projections 481 and a central electric contact 482 and is put into the hollow member 46 with its opposite projections 481 extending into the openings 465 the plate 48 is urged by the spring 47 so that the projections 481 abut against the edges of the openings 465 as shown in fig5 two terminals of the conductor 34a are connected electrically to the contact element 482 of the plate 48 and the wall of the hollow member 46 through wires 67 and 68 a wire 65 connects the contact element 482 to the contact element 15 of the socket 10 39 and a wire 66 connects the wall of the hollow member 46 to the wall of the hollow member 14 it can be noted that the socket 10 39 of the light device can be inserted into the connector 40 39 of another light device by engaging the protrusions 17 of the socket 10 39 in the angled end of the engaging holes 463 of the connector 40 39 in this situation the contact element 482 of the plate 48 is urged by the spring 47 to contact against the contact.