@LightBulbFun
Yes! Exactly like that, I didn't know those existed. Why aren't they all like that?

you mean like the

WRTL Thryactor?

https://www.lighting-gallery.net/gallery/displayimage.php?pos=-184846

or the Venture SZ090K245

https://ledspares.co.uk/products/sz090k245

or the


ok ill stop now


most modern SOX ballasts *are* like that.... (for those with arc voltages compatible with 240V OCV, those of higher arc voltages are run on lower-loss CWA setups sometimes)

@LightBulbFun
Yes! Exactly like that, I didn't know those existed. Why aren't they all like that?

Lamps like HPS and PSMH have relatively low open-circuit voltages because they use ignitors to strike the lamp.

MV lamps use an OCV of around 240V to strike, which is around as low as you can get considering the running voltage of ~130V. I hear that the OCV has to be around double the running voltage for an arc to be stable. MH is very similar (around 300VOC).

But with LPS this doesn't seem to be the case. For example, a 90W SOX lamp has an arc drop of 112V. This means that this lamp can run with an OCV of around 230V. But it can't strike on voltages that low, which is why the ballasts output ~480VOC. But isn't this wasteful? Why not just have a ballast with 230VOC with a ~1kV ignitor? I feel like this would be easiest to manufacture and also more efficient.

Any thoughts?

you mean like the BSX90?

https://www.lighting-gallery.net/gallery/displayimage.php?pos=-204553

Lamps like HPS and PSMH have relatively low open-circuit voltages because they use ignitors to strike the lamp.

MV lamps use an OCV of around 240V to strike, which is around as low as you can get considering the running voltage of ~130V. I hear that the OCV has to be around double the running voltage for an arc to be stable. MH is very similar (around 300VOC).

But with LPS this doesn't seem to be the case. For example, a 90W SOX lamp has an arc drop of 112V. This means that this lamp can run with an OCV of around 230V. But it can't strike on voltages that low, which is why the ballasts output ~480VOC. But isn't this wasteful? Why not just have a ballast with 230VOC with a ~1kV ignitor? I feel like this would be easiest to manufacture and also more efficient.

Any thoughts?

Bimetallic strips for use in temperature protection and circuit breakers are usually sort of cup shaped (like a pop-it) which gives them some snap action when they open and close. That's good for electrical loads because it quickly connects and disconnects, avoiding any arcing. But this seems to not be the case for fluorescent glow starters, the bimetallic strip bends until it just barely makes contact and then immediately starts to bend away. This means that they only make contact for a split second, which might not preheat the tube enough and so they might have to cycle again and again.

Why don't they use cup-shaped bimetallic strips for fluorescent starters? Then they would glow, snap shut for a good long preheat, and then snap open for a nice sharp flyback pulse.

There has to be a good reason why they don't do this, what is it?

Update - I never thought this would ever happen, but https://youtu.be/1Vjd6NmA9Hs?si=Q8FeE5m7VTbl1bv0 this video (skip to ~2:30) that dropped yesterday pretty much confirms what I suspected. James Cameron says that they went around LA with a light meter looking for streets with bright enough lighting to shoot night scenes on, and explicitly says they settled on streets lit by mercury vapor lamps.

I don't know, but I get the impression that stadiums were some of the first places to use metal halide lamps when it came to efficiency replacements, whereas most other mercury vapor lamps got replaced with HPS, since the CRI of HPS lamps is far too low for stadiums. Pretty sure some of the oldest MH lamps I've seen are stadium fixtures. Someone who's more familiar with the lighting from this time period will definitely know better than me though.

Advance RC-2S85-TP is the 120v version of the ballast posted above.

For shorter lamps and for converting existing fixtures the Universal 631-LH-TC-P is probably a better option. The OCV is lower so shorter lamps aren't as likely to instant start and the shorter ballast height means it will fit into more fixtures compared to the Advance.

Yes, I had come across that one and didn't buy it for that reason.

Detroit used to do this all the time with their series circuits, since it was easier to run regular secondary wiring instead of stringing the series circuit all the way to a pole that may sit out of the way. In this case I'm not sure why, as this appears to be a regular streetlight circuit.