When I read the 30/40w lable rating I was thinking the same thing myself.

Hey I finally figured out how to post pics now

How old do you think that ballast is?

Because rated for both 30 and 40W, the arc current would be somewhere below 0.35A [...]

The label on that ballast means the F30T12, not the F30T8. That's a rapid start ballast, and so can't run the latter lamp. The F30T12 is 90V and 0.43A.

That ballast would be from the 1950s, and could very well be full power. It's LPF though, so once the lamp reaches full arc voltage, it probably would be less than the full 0.43A.

If you're still considering a fluorescent lamp ballast, look for the Advance R-140-1-TP. It's a modern, single lamp, HPF, full power F40T12 ballast. I have one which powered my own 50W MV fixture for a long time.

I got my VS 50W MV ballast in 2013 if I still remember. The ballast costs me HKD$98 (about USD$13, or £8)
Pretty good ballast these, but runs a bit too hot!

Where did you get it? Also, your blacklight ballast should work. The lamp will be slightly underdriven, but it sounds like that is what you want. Good luck.

I tried using a 35w HPS choke (without igniter) to run them, it worked well for one of my 40w MV lamps but not my others of a different brand. The 120v OCV was not very reliable at starting them and they would cycle, except for one of my lamps which would stay on. Not sure how it would work for those in the 220v world

I tried using a 35w HPS choke (without igniter) to run them, it worked well for one of my 40w MV lamps but not my others of a different brand. The 120v OCV was not very reliable at starting them and they would cycle, except for one of my lamps which would stay on. Not sure how it would work for those in the 220v world

In the 220V world the MV's work well on virtually anything, what limits the current to the correct value, except a capacitor (capacitors generally do not match with any discharges), it could be any inductor (mix of ballast chokes,...) or a resistor (an incandescent lamp or heater),...

I have tried a 35/55w HPF SOX ballast with a 50w mercury vapour and it ran very well! Ballast did not get hot and lamp was bright..much better than on 40w T12 ballasts. I will be doing more tests in the coming days with this.