Could halide salts or sodium be added to mercury arc tubes in any amount to improve lumens per watt?

I ask because during warm up halide salts increase the chances of the arc extinguishing. Hence why they require a CWA ballast that has both a high OCV and warm up voltage.


However, I did find this providing evidence of less intensive warm up voltage requirements:


http://hid.venturelighting.com/VLPS/BallastDataSheets/PSMH/V90U7421.pdf


A much lower arc voltage:

https://products.currentbyge.com/sites/products.currentbyge.com/files/documents/document_file/84586_Chroma_Fit_Sell_Sheet.pdf


I'm wondering if there is any way that a metal halide bulb could be constructed where a 240 volt sine wave voltage can strike an arc, and if the bulb can warm up without an inductive ballast. Or at least a 240 volt choke without the help of an HV igniter.  


Also, would such a bulb be worth the added cost?  

  

Could halide salts or sodium be added to mercury arc tubes in any amount to improve lumens per watt?

Yes, it was done and the products then became known as "Metal Halide" lamps ;-)

The problem with sodium is, it tend to react with the quartz and forms dark brown stains, blocking light and become brittle. So any sodium (or other such metal) has to be "accompanied" by some element which the sodium "likes more" than the quartz. The halogen elements were exactly such elements, which let the sodium to be freed only within the hottest core of the main arc stream (so it could do its high efficacy light generation voodoo), but keep the sodium "occupied" elsewhere in the burner, mainly when close to the quartz tube body. Plus of course, the resulting salts should be easy to evaporate, so the compound may reach the hot arc plasma. Again the iodine is good at it...

Also: You need to disconnect the starting probe when the lamp is at full regime, to prevent the halides to corrode the area of the starting electrode which is sensitive. This is done by a bi-metal, that shorts between the starting and the main electrodes. Also, you shouldn't operate the lamp with the base-down, even if it is for universal burning position, unless the lamp is rated for base-down use only.

Yes and Yes, but how to over come the arc extinguishing on a none inductive ballast during warm up? Or at least on a reactor type?   

The reactor type ballast crosses zero current when there is nearly full mains peak voltage available for the reignition in the opposite polarity, so the MH work well.

With a resistive ballast there is too long gap with insufficient voltage, so the reignition is not possible then.
The only option is to maintain the ionisation with some auxiliary circuit, like the GE Halarc uses (the reason for a DC tube there is just the ability to get such thing without any complex electronic - there it is in the form of a higher voltage supply with a series high ohmic resistor, the main circuit is then separated by the main rectifier diodes when the mains goes too low)

The problem is, the halogen atoms are very hard to ionize (they are already lacking one electron for a complete orbit, what makes ripping one other off way harder), so the halides are just cooling down the arc and during zero cross in fact "eating" any free electron they meet, further making the reignition harder, in other words halides tend to quench the arc.

And then the conductive nature of the molten salts causes an electrolysis corrosion problems once the salt covers two conductors with voltage across it (e.g. the main vs auxiliary electrodes), what makes even the auxiliary probe unusable to act as a reignitionk aid (otherwise making the MVs so easy in maintaining the arc even with a very high arc voltages vs the ballast OCV), because to prevent the corrosion it has to be deenergized (by the bimetal switch in a typical probe start MH design) once the salt is molten.


In fact the idea to add other components to the mercury to boost the efficacy and/or color is going all along the MV development, but it always hit some roadblock effect mainly in the reliability.
What later became known as the MH design was the only real life proven way to make the generic idea commercially viable, even if it has quite a lot of shortcomings (need for higher arc loading so higher pressure leading to quartz deterioration over time, fill attacking the arctube material even when that was slowed down significantly by the halogens in the fill compounds, fill material loss requiring very temperature sensitive saturated vapor concept to keep their working pressure optimal, need for higher OCV ballasts, the impossibility to use a resistive ballast so the impossibility of a selfballasted lamp without more complex electronic being one of these shortcomings too...)

Thank you- and yes- I fully agree. Even with the commercially viable lamps there are a lot of downfalls like lumen maintenance being very poor and color shift.


So in Mercury vapor the aux electrode actually aids re-ignition?


What about just sodium mercury amalgams in the arc tube? Obviously quartz alone wont work, but could you make a commercially viable arc tube that also takes a starting electrode?   


 

Is this a mercury ballast trying to start the bulb?


https://www.youtube.com/watch?v=qxan2dzkpRU

Thank you- and yes- I fully agree. Even with the commercially viable lamps there are a lot of downfalls like lumen maintenance being very poor and color shift.

The color shift is the result of alterations in the thermal balance as the lamp ages, yielding shifts from optimal fill component pressures (some are saturated vapor, some unsaturated, so when hotter, the pressure of the saturated ones increases, making their emission stronger, so shifting the color).
And the faster lumen depression compare to the MV is caused by the inability to use the "anti-darkening" electrode design, because these do not like the higher operating temperatures and mainly the chemical environment in the MH arctube. So the electrodes have to be just tungsten alone, which leaves black sputtering deposits.

So in Mercury vapor the aux electrode actually aids re-ignition?

Yes, it is the place with the closest gap between the electrodes, with no discharge becomes exposed to the full ballast OCV. That allows with e.g. resistive ballast after a zero cross to form a small discharge there even before the mains voltage even climbs (along the sinewave) to the nominal arc voltage, this discharge then generates free electrons/ions directly and around the opposite electrode even indirectly via a photoemission, so once the voltage reaches the equilibrium level (what is then the arc voltage), the avalanche ionization then goes pretty fast to reestablish the full fat arc for the following half cycle.

What about just sodium mercury amalgams in the arc tube? Obviously quartz alone wont work, but could you make a commercially viable arc tube that also takes a starting electrode?   

The problem is, what material will you then use for the arctube?
Quartz is attacked by the sodium unless you use the halogens.
PCA can stand the sodium well (all the HPS out there), but it is hard to form into any complex shape and to make seals around any lead wires. Hence the HPS are designed with the minimum electrodes (just the two main ones) and the ignition is done by using the high voltage pulses and arc maintenance (reignition,...) by using higher OCV margin (that is why HPS designed for 230V have arc voltage below 100V).

Is this a mercury ballast trying to start the bulb?

https://www.youtube.com/watch?v=qxan2dzkpRU

Maybe, but I would rather guess a bad ballast (EOL capacitor)

Do all MV lamps have anti-darkening? Or just those like the Bonus line lamps?

Do all MV lamps have anti-darkening? Or just those like the Bonus line lamps?

I would guess all newer ones yes (based on the white deposit they form as they age). But in most modern ones it is used in a way to boost the initial efficacy by designing smaller, higher loaded arc tubes. So although the "anti darkening" does make the wear less degrading, the high loading makes the wear faster. So at the end it barely compensates out life wise (compare to old lamp designs prior to the anti darkening electrodes), just allow higher efficacy mainly for lower power lamps.
The result is still quite flat lumen maintenance during lamp rated life, but then very steep degradation at the EOL.

I've noticed the 120 watt looking arc tubes in 175 watt lamps. How does this improve efficiency? Warm up? Re-strike? Electrical characteristics? 



https://www.youtube.com/watch?v=teLNGJ9BpH4

I've noticed the 120 watt looking arc tubes in 175 watt lamps. How does this improve efficiency? Warm up? Re-strike? Electrical characteristics? 



https://www.youtube.com/watch?v=teLNGJ9BpH4

Just a higher arc loading. The tube is shorter and with higher pressure.

Follow-up question: What would happen if they used something like cesium or rubidium instead of sodium?

Follow-up question: What would happen if they used something like cesium or rubidium instead of sodium?

Everything from the first column of thr periodic table will attack the quartz in a similar way. And to prevent that, it would need something from the second last column as a preffered "target" to form a compund with.