Narva 100/150W operations theatre lamp of the old design

Before modern compact halogen and later LED Solutions came to the marked, Operations theatre lamps were globe shape frosted incandescent lamps if medium power in the are of the lower 100s of watts. These lamps were bot frosted and clear depending on the fixture design and manufactured by several manufacturers.
The lamps however featured a novel feature: They had two filaments, but unlike most dual filament lamps the Filaments have different operating voltage. Reason is simple, while hospitals are generally equipped with backup generators it is highly undesirable for the operations theatre light to go out during an operation. Therefor these light had build in back up batteries. However these batteries were low voltage an in the absence of power electronic that voltage could not be stepped up. That meant that the second filament would be off the low voltage variety.
This particular lamp was made by Narva in ist special and high power incandescent lamp factory in Plauen Germany in the 70s. It features a main filament rated 220V 150W and an auxilery Filament rated 2eV and 100W. The base is evolved E40d lamp with the middle contact beeing elongated allowing bigger contact area for the high current low voltage filament.