Bumix "Jupiter" Mercury-Tungsten Mixed Light Lamp

Here is a rather special and rare lamp, I have not come across one quite like it before. I don't have all the technical details, but basically it is a blended mercury/tungsten lamp, but with the arc tube and filament separately wired to the 3-contact cap, so either can be lit independently or together, although in normal use the filament was wired to a tap on the ballast so it was always on, in order that there was always light if power was applied, such as in a hot restrike situation. The lit images are just after ignition, with the filament at approx. 140V via the Variac, and at full brightness.

Unusually, the arc tube is made of aluminosilicate hard glass rather than quartz, and does not have an auxiliary starting electrode, so an ignitor is necessary. Originally this was provided by the control gear, in which a capacitor and bi-metal thermal starter were used to provide an inductive voltage pulse from the ballast. Here, it is simply lit using a 125W MV ballast and a standard 3-wire HPS/MH ignitor.

Finally, thanks to Andy (Photonicinduction) for parting with this amazing lamp..!