Here are two Advance YS-2S85-TPs. Each one can power 1 or 2 tubes. Kind of expensive but it is a pack of two ballasts.
https://www.ebay.com/itm/255543314322

Yes, it’s more of a cyan colour 😎

The white-ish light from an uncoated lamp does not look green. It looks a blueish white to most people. But then you let someone look at their hands - zombie colors.
It's one demo i do at work at talks about lamps and color rendering.

I'm looking for an F36T12/HO 2 or 1 lamp ballast. I found some lamps and I want to convert some fixtures to them. It needs to be 120v. I'm hoping someone knows the model numbers of the ballasts?

The lamp power factor consists of both Harmonic power factor and Displacement power factor :

The Harmonic power factor is result of the voltage waveform, approximately square. This accounts for most of the lamp power factor

The Displacement power factor is result of the lamp reignition behavior after zero crossing, where each half cycle begins with a high voltage overshoot before the flat area of the voltage clamped by the arc. Part of the voltage waveform is leading before the current peak, but in terms of the current that's lagging

The significance of the latter effect may vary based on lamp technology, on how much the specific lamp is pushing the stable Varc limits (higher power lamps are naturally more stable, but then they are also designed with higher Varc so push the limit as well), and how hot the lamp is



Then we have the ballast resistive losses, which sum up with the lamp Varc according to your old formula. If we account for them, the new formula will be :

Vballast_reactance = sqrt( Voc^2 - ( Varc + Vballast_losses )^2 )
I = Vballast_reactance / Xballast

Vballast_losses approx = ( 1 - BallastEfficiency ) * Voc

HID ballasts (series choke, and probably HX choke part bahaves the same) have typical efficiency around 0.90..0.92 for >100W lamps, 0.85..0.87 for <100W lamps

This is almost exactly what it should look like: https://www.lighting-gallery.net/gallery/displayimage.php?album=7562&pos=1&pid=249898
That's a 400w one caught using a film camera. I corrected it to look like real life.

@RRK
Wow, I am very pleasantly surprised that I got that right. So I just accidentally calculated average power factors for different lighting technologies. This is all coming together. That means with a given technology with given specs, I can calculate the impedance necessary to ballast it. Very nice.

Yep this is a lamp 'power factor' but not the power factor in the meaning of the school-level classic circuit theory (which is just a phase shift).

Lamp voltage is not near sinewave (see here for my real life captures https://www.lighting-gallery.net/gallery/thumbnails.php?album=7753) and this is what throws off the result up to 20%.

@Ash
Alright I did some more figuring.

This equation works very reliably, and I would like to use it, but I have some questions.

I was using this equation in conjunction with ohm's law to calculate desired ballast impedance when given lamp voltage, circuit voltage, and lamp current.

This consistently overshot the specified impedance necessary for the lamp based on datasheets, but very precisely. For MV, it was almost exactly 20% overshooting, for MH it was more or less 15% overshooting, and for HPS it was pretty consistently 10%. I took the averages of all of the overshots and then the inverse and got these constants to multiply with the results to get the right approximate answer:
MV:  0.831
MH:  0.873
HPS:0.913

This is okay, all I have to do is remember these numbers when calculating. But I want to know where they came from. Is this the power factor of the discharge itself? That is what I am thinking, but I don't know for sure. I can't think of any other reason it would be so consistent across different wattages but so different between different HID technologies. I have yet to try this for fluorescent and LPS lamps but I might do that later.

Thanks again.

@Ash
Thanks so much for that equation! I thought that would be based on some super complicated concept that I would never understand, but I suppose not. I will play with this a little more later today and see what I can learn from it.