🚀 go-pugleaf

The "filament" is actually the ballast.  Since the lamp is rated at 250 Watts
you will probably need to be able to pass about 5 Amps through the lamp.
If you don't pass enough current then the lamp won't get hot enough to
attain the curroct vapour pressure and will not work reliably.  If you use
incandescent lamps as a ballast you will need about 500 Watts worth I would
think (an incandescent lamp is almost a constant current device).  The filament
was possibly a barretter, an Iron filament in a hydrogen atmosphere for
current regulation.  I would expect that the mercury lamp drops about 30-50
volts in operation.

The 15 K resistor is probably to provide a voltage between the trigger
terminal and one electrode to ionize the mercury initially to start
operation.

Kevin White