ABSTRACT
Hg : Xe : Na : Sc : 1 = 2 500 : 10 000: 1 : 1 : 4 where the Na and Sc are responsible for the spectral radiation distribution and Hg establishes an appropriate lamp impedance R. This impedance should be about 200 SI to get a reasonable relation of discharge power to the electrode losses and to limit discharge current. The xenon is responsible for the generation of instantaneous light immediately after switching on. The voltage of the lamp UL is
2me (n.gQ,g +n XeQ Xe 2neQi) e e - ( 500 : 10 : 1 )
candescent headlight lamp. A scattering of the arc radiation in the tube wall would destroy the sharp luminance gradient at the contours of the arc and cause glare. Furthermore, it reduces the luminance of the arc which is responsible for the level of illuminance on the road at a given aperture of the reflector. Considering the high thermal load a transparent ceramic material should be used for the arc tube walls. We tested single crystal ceramics as well as sintered materials using a powder technology considering transparency, tolerable wall temperature and mechanical shock resistivity. As an example the results of a construction are presented which consisted of a sapphire discharge tube and polycrystalline alumina (PCA) end caps allowing a conventional sealing technique for the electrode systems (Fig.1). The ceramic parts were combined by a sintering process without a frit. The arc tube was designed for operation in a vacuum outer jacket. Fig.I.Ceramic Automotive HID lamp consisting of a sapphire capillary and two PCA end caps. Capillary ID = 1.5 mm, electrode tip distance 4.2 mm. The tungsten electrodes were sealed with niobium feed throughs using glass fit .
