This is purely a thought, but would it be possible to run SOX lamps in series; where the live from the ballast goes to one lamp, the other end of the lamp connects directly to a second lamp, and the neutral coming off the second lamp, with an ignitor bridging both of them. Would it be possible? Let's say using a 35 and a 55W lamp for a total of 90 watts. Would a standard 90W SOX ballast work, or would it need to e more powerful because of two arcs instead of one?

Just asking out of interest

Absolutely not. A 90w sox lamp runs on 820mA, while the 35w runs on 510mA and the 55w on 520mA.

It is completely unpredictable what current will actually flow, because the voltage drop of the lamps is heavily dependent on whether they've already warmed up or not. It is unpredictable what will happen if one lamp will vaporise its sodium earlier than the other. Arc lamps are highly unintuitive things, it's not like you're connecting two incandescents in series.

The voltage drop also gets awfully close to mains voltage (assuming 230v) which means that the tubes might only light during the 'topmost' parts of the AC cycle.

If you want to experiment with mismatched tubes in series, try it out with bog standard fluorescents first. They don't completely behave like SOX lamps, but at least you can get some valuable experience dealing with negative resistance lamps that can get into a runaway state.

In theory, it may actually be possible to run them from a current limited ~520mA AC supply, but it will need to be an actual regulated power supply that keeps current (not power!) exactly at 520mA, regardless of the load connected to it.

Thank you for your input. I was not actually thinking about doing it, it was just a theory. I threw together a quick demo of what I was talking about and made the post.
Again just a theory, You're saying it would be easier to run two matching lamps (say both 35W), but again you need a specialist limited power supply?

I know twin circline FLorescent fixtures came in 22 - 33 watt twin tube but other then that one application every 2 tube one ballast fixtures are designed to run the SAME lamps in both positions

I once tried 2, 125 watt mercury lamps on a 250 watt ballast!, that didn’t work either! 

Thank you for your input. I was not actually thinking about doing it, it was just a theory. I threw together a quick demo of what I was talking about and made the post.
Again just a theory, You're saying it would be easier to run two matching lamps (say both 35W), but again you need a specialist limited power supply?

your best bet for running 2 SOX lamp in series would be using a classic SO/H/ SOI/H 45-60-85W leak transformer ballast if ya have such a device, leak transformer ballasts are more or less constant current drivers, and 2 26W SOX-E/35W SOX's in series are approximately equivalent to an 60W-85W SOI/H, the only problem is starting, the OCV might not be enough to start 2 in series at the same time, so you might have to link one out at first let the other strike then remove the jumper to strike the other lamp


SOX lamps come in current ranges so with the right constant current source you could drive non equal lamps together as long as they are within the same range, for example you could drive a an 18W SOX-E 26W SOX-E and 36W SOX-E all in a string together (all are ~0.35A~ lamps), or 90W 135W 180W (all are 0.9A lamps) or if you really wanted to take the biscuit you could in theory do 35W SOX 55W SOX 66W SOX-E 91W SOX-E 131W SOX-E all in a string since they are all 0.6A lamps, but you would need a seriously beefy constant current 0.6A supply for that!