Osram GEC 995-9703 for Westland scout helicopter

Here you can see a lamp used in the Westland scout helicopter of the british and commonwealth armed forces. It is believed that this lamp was used as the main "Headlight".
The lamp is of fairly compact proportions for its rated power of 500W max. Like similar projector or car headlight lamp the lamp filament is overdriven giving the lamp a higher colour temperature and minimally higher efficiency while limiting the lamp life to 50 hours. This however can be accounted for in the service work after each flight of the aircraft.
The lamp contains one high current C-2 single coil twin pillar design and one one CC-8 axil double coil tungsten filaments. Due to the lamponboard voltage of airplanes of nominally around 28V these filaments are of a high current design (hence single coil) and ned substantial lead in wires witch are several mm thick in this lamp. Due to the high lamp current of about 20A for the main filament and 10A for the auxiliary filament, the main filament is rated slightly below nominal voltage in order to compensate for the voltage drop of the wiring to the lamp.
In order to securely connect and mount the lamp a special property cap is used. While Large Prefocus caps like P40s showed that they can handle high lamp currents (I have example of lamps drawing more than 30A with that cap used by the RAF) and allow precise location of the lamp in the fitting. While also double contact lamps were made for similar use, the smaller centre contacts may have gotten contact difficulties, leading to overheating.
Therfor this lamp has a unique special cap: Harley 10B/101
This cap consist of a heavy copper tube turned down on a lath. Pins ensure precis alignement in the fitting. The lamp is connected via three bolts on the base of the lamps which are mounted in an asbestos block.

As there a still a few of these helicopters in use, there is small marked for replacements if the aircrafts have not been refitted. The small lamp manufacturer Victory lighting in Wembley England. Victory emerged from the MOD contracts of GEC when Osram acquired it and stopped manufacturing these lamps. Later they would also take over the similar contracts from GE Thorn. Generally some lamp parts, especially the caps would be reused.