I recently purchased a refractometer which came with a Philips 93109e low pressure MV spectral lamp, specifications are 14v, 0.9A, 12W, ignition 400v.
Unfortunately it didn’t come with a power supply, could someone explain to me what I need to get this lamp working.

I do have a 1 amp variac some chokes and capacitors but not sure what values I would need and how to wire them up.

This website  http://www.extra.research.philips.com/hera/people/aarts/_Philips%20Bound%20Archive/PTechReview/PTechReview-11-1949_50-299.pdf  does show a circuit diagram on page 2 which seems too simple to me for a stable light output.

Your help would be greatly appreciated.

The ballast depicted is a HX autotransformer, to make the required 400V for ignition.
Because the arc voltage is just 14V, I would expect it to be very ineficient and bulky for just 12W, but with such lab instrument, who cares.

So back to what to use:
Apparently the lamp needs 400+V for ignition and then the short circuit (the 14V of the arc voltage is really a short circuit for a 400V OCV ballast) current about 0.9A. So for ballast dry run tests, you may just short circuit the output and do measurements.
What would work towards the lamp is some series HID choke leading to the 0.9A of short circuit current, plus some ignitor (prefferably LPS parallel one because of a lower voltage - here you dont need kVs). But because of the low arc voltage, the coil would operate at a higher current than originally designed and so may overheat, if operated for longer than few minutes.
When you want to operate it for longer, I would use some ballast coil designed for the 0.9A (European 70W MH/HPS) with a series capacitor, so the short circuit current would be the 0.9A (for the 230V/50Hz it would be 6.43uF 450VAC motor run capacitor combination, for 120V 60Hz it would be 50W HPS choke and a 10uF 250V motor run cap). Adjust the exact capacitance so the short circuit is at the required 0.9A.

As the ignitors any fluorescent starter (designed for series chokeballast operation) in series with about 0.3A (25..40W for 120V and 60W for 230V area) incandescent could be the first experiment to try.
But even standard HPS ignitor will work if you are careful enough to not energize the thing with no lamp in the socket (with the lamp there, the voltage will be always clamped by the lamp to a safe level for the socket, but with no lamp, it may reach the full kV and be arcing there). With the series capacitor and a semiparallel ignitor (mainly using the US HPS ballast) the capacitor has to be on the mains side, so the capacitor does not interfere with the ignitor (the ignitor uses the ballast choke as a HV step up pulse transformer)

These 0.9A spectral lamps were built for use on ordinary LPS 90W leak transformer. That’s what I did learn about this lamp type. Alternative sources I’m not aware of.

Thanks for your quick reply, interested reading looks like I'm going to do some experimenting.