Rounded end halogen lamp with exhaust tube having different glass

Claim 1

An improved incandescent lamp comprising an envelope of a first high temperature aluminosilicate glass exhibiting a sealing temperature not exceeding about 1450° C. comprising in approximate weight percent 54-71 SiO 2 , 12-18 Al 2 O 3 , 4-8 CaO, 10-23 BaO, and 0-3 R 2 O, wherein R is an alkali metal ion, along with minor amounts of incidental impurities, residual fluxes and refining agents, such that the aggregate SiO 2 and Al 2 O 3 content lies within the approximate range 73-83 weight percent, the aggregate BaO and CaO content lies within the approximate range 17-30 weight percent and the ratio between BaO weight percent and CaO weight percent lies within the approximate range 2.3 to 3.5, said envelope also having a rounded end, refractory metal lead-in wires hermetically sealed into said envelope at one end of said envelope opposite said rounded end, a tungsten filament connected at each end to said lead-in wires, said envelope containing the tipped-off residue of an exhaust tube prepared from a second different higher temperature aluminosilicate glass located at the end of the envelope opposite the rounded end and exhibiting a higher sealing temperature of about 1500° C., with said different higher temperature aluminosilicate glass comprising in approximate weight percent 56-63 SiO 2 , 13-17 Al 2 O 3 , 19-24 BaO, 1-4.5 CaO, and 0-3 R 2 O, wherein R is an alkali metal ion, along with minor amounts of incidental impurities, residual fluxes and fining agents, such that the aggregate BaO and CaO content lies within the approximate range 21-26 weight percent and the ratio between BaO weight percent and CaO weight percent exceeds 4.7, and a filling within said envelope containing an inert gas and a halogen, wherein the improvement comprises having said exhaust tube devoid of any conventional refractory metal spiral.