What size transformer do I need.

Factual Questions
1

Looking to run a 35 watt low pressure sodium vapor light with a 240 volt / 50 cycle magnetic ballast off US power. It seems the way to drive the lamp correctly would be to increase the voltage to compensate for the frequency difference. I know 277 to 120 transformers are extremely common, would using one of these in reverse be a good idea, or no? It does light being fed 240 / 60, but I’m guessing this is suboptimal. How many volt-amps would I need.

I’d rather keep the original ballast, both because 120 / 60 LPS ballasts are extremely expensive in the US and to keep the fixture authentic

2

I would just get a 120-240 Step-up transformer (or autotransformer) that can handle 100W or so and be done with it. If anything, going from 50Hz to 60Hz increases the power to the lamp, so you might need to run it at less then 240V for it’s rated power. But, I wouldn’t worry about it.

3

Have you had a look at the ballast itself? A fair number of them are built to run on 120 to 277, just by selecting the appropriate wires or taps.

Just curious of the love for sodium…it’s one of the few light sources I despise because it’s so yellow and kills all hope of color recognition.