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?

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

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

@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)

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?

Almost certain, since electricity is relatively inexpensive in USA, manufacturers preferred extremely robust, but really inefficient high-OCV leak transformers. Back in 1970-1980s semiconductor circuits were still considered a big step back in terms of reliability.

@LightBulbFun
Very interesting, I don't think any choke ballasts were ever made for LPS in the US but I may be wrong. Are there any US-based ballasts for LPS lamps that use ignitors that you know of?

@RRK
But isn't the whole point of LPS to have higher efficiency than HPS? Unless we are talking about the pre-HPS years here. I thought that was the whole LPS mission statement, to be the most efficient lamp. Were they still more efficient than HPS even when considering these high ballast losses?

AFAIK, LPS lamps were not especially popular in USA compared to Europe. May be no one really bothered to optimize ballasting for somewhat niche product. You can also consider reduced service costs vs saved electricity cost.

Sure, poor ballast efficiency very much likely driven system efficiency of American LPS luminaries below of what is achievable with HPS lamps.

Many US luminaires used the same type transformer ballasts for HPS as well, despite many of them running on 240V and 277V

And many also have ignitors made in open frame, a bare conductors high voltage circuit operating in the filthy and damp environment inside the gear compartment of a cobrahead. Not great reliability either (and by far more likely cause of failure than internal failures of electronic components)

So, the consideration was apparently not efficiency and not reliability, but something else. Maybe :

 - Wanting an universal ballasts that includes also 120V as an input voltage option. This requires a transformer, and if so, just add taps for the other voltage options. (Still does not explain why not make completely separate, and more efficient, ballasts for each input voltage range. Even the 120V ballast would have good efficiency improvement and cost reduction from not having to contain additional winding for the higher voltages, unused at 120V but taking up space, that could be used for thicker wire in the other windings instead)

 - If the ballasts are CWA, better resilience to line voltage fluctations

@RRK
Yes, they really didn't catch on here, very unfortunate.

@Ash
I should have specified:
I don't mean having choke ballasts on 240V, that would just be barbaric (ahem europe) just kidding
I mean just having CWA (ew) or HX autotransformer ballasts that output a lower OCV but in conjunction with an ignitor. Choke ballasts are barely ever used here, presumably because of the wide range of voltages we have available. Even the 120V HPS chokes are kinda rare to see.

I have seen those open-air ignitors on Ebay, those are disgusting. As much as I like to be able to see what is inside electronic devices, ignitors are definitely ideal candidates for potting.

Yeah my understanding was that LPS was a niche enough item in North America that ballast manufacturers never bothered to adapt the choke + ignitor setup common in newer European LPS ballasts to North America.

Same goes for electronic LPS ballasts. It's unfortunate since a lot of lower power leak transformer based 120v LPS ballasts were fairly lossy and resulted in a fairly low system efficiency compared to HPS. Even LPS ballasts designed for higher voltages such as 240v, 277v, 347v, and 480v remained based on leak transformers. It's too bad electronic LPS ballasts were never developed for 120v as well. I could see why the choke setup never made it here due to insufficient OCV on 120v but it seems like a electronic ballast might have been easier to adapt.

Now I suppose if LPS was more common here, something like a PSMH HX ballast might have been developed for LPS, only a modest step up to avoid the lossy leak transformers and then a ignitor to provide the starting voltage. I suppose ballast manufacturers did the math and figured the cost of NRE for developing such a ballast for 120v was more than any potential increase in sales compared to the existing leak transformer ballasts.     

If transformer is a given, the higher Voc has only indirect effect on the efficiency :

 - The difference between Voc and Varc (Vballast, with the root formula) is dropped on the ballast impedance. As the ballast impedance is not a resistor, this (in theory) does not waste any power even when Vballast is high

 - The higher Vballast requires more turns in the ballast's secondary winding. If instead lower Voc would be used, this would require less turns, freeing up space, and allowing the remaining turns to be made with thicker wire, reducing its resistance and therefore losses. (With some relocation of the leakage paths in the core, there could be room made to push some of the wire gauge improvement to the primary winding as well)

Maybe the difference (via the ballast wire gauge) was not deemed significant enough, and they preferred to eliminate the ignitor instead

(And maybe this was a design choice from the early days of the technology, that just wasn't changed because dont fix whats not broken, even when in later years the cost of ignitors went down and copper and electricity went up)

LPS would work well with Instant Start FL ballasts matching by current, and those are available for 120V

Yeah it seemed like it would be fairly easy for a manufacturer to modify one of those designs for LPS, modifying the design to match the current of a LPS lamp and also modifying the wiring shouldn't be take too much effort.

@RRK
But isn't the whole point of LPS to have higher efficiency than HPS? Unless we are talking about the pre-HPS years here. I thought that was the whole LPS mission statement, to be the most efficient lamp. Were they still more efficient than HPS even when considering these high ballast losses?
[/quote]

LPS started way before HPS, so yes, we practically are talking about "pre-HPS" years, when the main standards (how the lamps "are normally handled") were set. Then it was just the "It was always made this way" inertia in the industry.

Not all the things that happen in the lighting industry are completely logical


@Ash - forcing a leak transformer to have a higher OCV at the same current increases losses / weight / costs proportionally due do the necessity of having proportionally higher reactive power, so more turns at secondary, heavier core and thicker winding at primary.

There are saturation tricks in leak transformers allowing to get peaky output voltage, but these are likely taxed with higher losses too.