| abstract |
A lamp having an arc tube with a light-transmitting envelope is provided. The arc tube is surrounded by a gaseous medium defined by containment envelopes such as hermetic shrouds and the like. The gaseous medium is preferably He or H 2 or Ne or another gas whose thermal conductivity is higher than the thermal conductivity of N 2 at 800 ° C., or a combination thereof, to assist in cooling the arc tube. The interior and / or exterior of the shroud may be covered with a diffusion barrier. The gap between the shroud and the envelope can be made small to help cool the hot spots of the arc tube, the shroud wall portion near the arc can be thickened, the arc tube can be offset above the transverse axis of the shroud, and The return lead of the arc tube can be disposed between the shroud and the arc tube. |