11 that is screw has two annular portions whose connecting portions define respective undercuts 11 a 11 b used for fastening purposes advantageously that way besides fastening the junction piece 8 to the base 43 the fastening member 11 also increases the packing effect between the covering element 3 and the selfsame junction piece 8 that is the printed circuit 5 in the embodiment illustrated the covering element 3 has a plurality of holes 12 located at only one half part of the lamp indeed in this embodiment the lamp 1 comprises at least one tongue 20 protruding laterally from the covering element 3 on the other half part and irremovably connected thereto more specifically the tongue 20 is defined by a thin metal plate interposed between the sealing material and the covering element 3 and protruding laterally substantially parallel to the mounting surface u201c a u201d alternatively the tongue might also consist of a protuberance of the covering element 3 in this regard the base 43 has at least one peripheral shoulder 43 a provided with a respective peripheral groove which is engageable with the tongue 20 to fasten the base 43 to the covering element 3 in conjunction with the fastening member 11 advantageously that way installing and fastening the lamp is quick and easy because it is sufficient to slide the tongue 20 into the groove 44 and tighten the fastening members 11 screws into the respective half part it should be noted that what is described in connection with the embodiments illustrated in fig1 to 5 where applicable and not in contradiction also applies to the embodiment just.