the tube is closed by a pinch 23 which forms a hermetic seal the illustrated lamp is limited to a base down operation wherein the longer exhaust tube 18 which must be the coolest portion of the arc tube for the analgam to condense therein is located lowermost the arc tube is supported within the outer envelope by means of a mount comprising a single rod 25 which extends the length of the envelope from in lead 7 at the stem end to a dimple 26 at the dome end to which it is anchored by a resilient clamp 27 end cap 13 of the improved arc tube is connected to the frame by band 29 while end cap 12 is connected to in lead 6 through band 30 and support rod the inter envelope space is desirably evacuated in order to conserve heat the evacuation is done prior to sealing off the outer jacket a getter suitably bariumaluminum alloy powder pressed into channeled rings 32 is flashed after sealing in order a high vacuum a method of manufacturing this type construction is further disclosed in u s pat no 3 708 710 which is also incorporated by reference and hence need not be repeated in connection with the present invention u s pat no 3 708 710 teaches the combination of a high pressure hps sodium vapor lamp in which an electron emission material is incorporated the composition of the material corresponds to that of the area designated a on the accompanying triaxial plot included in the drawings as fig3 in u s pat no 3 708 710 it is pointed out that the electrodes of the lamp are required to provide copious electron emission and to be resistant to vaporization and ion bombardment but.