Abstract: An arc tube of fused silica for a metal halide arc discharge lamp including a fill for the arc tube comprised of a sodium halide, at least one additional metal halide, and an inert starting gas, the arc tube including a tube of fused silica having an inner wall defining an arc chamber, the inner wall of the tube having provided thereon a metal silicate coating which is vitreous and light-transmissive, and which is comprised of a silicate of at least one metal selected from the group consisting essentially of scandium, yttrium, and a rare earth element, and preferably which is the same metal as that of the at least one additional metal halide. Protection of the fused silica arc tube with the metal silicate coating reduces loss of the metallic portion of the fill by diffusion or reaction and corresponding buildup of free halogen in the arc tube.

Abstract: An improved sealing composition for use between alumina ceramic parts, or between alumina ceramic and refractory metal, is based on 47 weight percent Al.sub.2 O.sub.3, 37 weight percent CaO and 16 weight percent BaO. Up to 3 weight percent B.sub.2 O.sub.3 may be added for improved wetting and flow characteristics. The composition has a lower liquidus temperature (1325.degree. C.) than an otherwise similar one previously used which included 5% MgO, and its thermal expansion coefficient is less affected by dissolved Al.sub.2 O.sub.3. As a result, a closer thermal match with alumina ceramic can be maintained during seal processing and the rejection rate is reduced.

Abstract: New sealant compositions for sealing end closures or inleads in ceramic envelopes are based on the system Dy.sub.2 O.sub.3 -Al.sub.2 O.sub.3 -SiO.sub.2. These compositions will withstand metal halides used as arc materials up to temperatures exceeding 1200.degree. C, and make possible more efficient lamps of improved color rendition.

Abstract: An improved electrode particularly suitable for operation at high current densities in vapor discharge lamps in which the pressure is upwards of 1 atmosphere. It comprises a porous matrix of refractory metal impregnated with a glassy emission material which becomes fluid or produces a fluid component at the operating temperature. The emission material comprises a low work function metal oxide and a glass forming component, preferred emission materials being lanthanum borate and lanthanum silicate.