Author Topic: Induce cycling in a streetlamp?  (Read 508 times)
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Induce cycling in a streetlamp? « on: January 03, 2020, 06:03:45 PM » Author: esti
HI all,

My topic was accidentally deleted by the mods so reposting here.  Medved - thanks for your replies, I had written back to you with some follow on questions:

Note about safety: My idea is to have a streetlamp lying on its side, so with HPS, in case it blew, there isn't anything to drop down from a height. So I presume that would be ok safety wise? There is also the bulb cover on the fixture itself.You mention that HPS could contain itself.

I had a questions about the structure of HPS lamps: You mentioned liquid. I understood the arctube to be xenon, sodium, and mercury vapour?
Also when you said they blacken causing them to run hot, is this blackening on the inside or outside of the arctube?


If we just consider HPS bulbs (and not MH) I had 4 possible ideas on how to move forward:

1) Find a place that has lots of spent bulbs and pick out the ones that cycle and use these. When bulbs get the phase in their life of cycling, do they remain in this cycling phase indefinitely? Or for days, months, years, before they stop lighting altogether?

2) Modify or have manufactured bulbs that will cycle from the start. Could this be done by 'blackening' (painting?) the arctube in some way (if its on the outside) before it's place in the outer vacuum glass bulb? I read that the loss of sodium escaping the arctube is an issue? Is there any truth in that? Perhaps there are people who custom make lightbulbs, if there is physical make-up that would incite cycling, i.e. less sodium vapour in the mix for example?

3) As you say, to over supply the bulb with a higher rated ballast for the bulb. Would there be any danger in this, other than it causing damage to the bulb? If you took a new bulb and gave it too much power, would it cause it to cycle initially?

4) Make a box that would cut power to the bulbs after a minute or so, and then reignite the start up cycle agin and again. Would this accurately display the same visual characteristics as a bulb that actually cycles? It would have the same start up process with the  visual changing colour of light. But does a bulb that cycles, burn brighter and brighter than normal operating brightness before cutting out? Or is a cycling bulb just one that can't sustain itself for a period of time and the brightness never eclipses a normal working bulb?

Many thanks to everyone who can help on this project


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Re: Induce cycling in a streetlamp? « Reply #1 on: January 04, 2020, 06:25:36 AM » Author: esti
Yes, Iíll be working with an electrician on this as it is for public presentation. Before that, I think this project requires more specialist advice though about the intricacies of street lamps and their behaviours with cycling to guide what an electrician would be being asked to do. Thatís why Iíve come to this forum to ask people who know about these things!  :)

If anyone is willing to be an advisor or consultant on this project I would love to hear from you.
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Re: Induce cycling in a streetlamp? « Reply #2 on: January 04, 2020, 07:18:58 PM » Author: Medved

Note about safety: My idea is to have a streetlamp lying on its side, so with HPS, in case it blew, there isn't anything to drop down from a height. So I presume that would be ok safety wise? There is also the bulb cover on the fixture itself.You mention that HPS could contain itself.

Normally it does, but first this assumes nobody is actually abusing the lamp in any way (so no overpowering, e.g. in an attempt to make it cycle or so) and second it is not 100% guaranteed.
All makers (formally) explicitly require all lamps to be enclosed in a luminaire that is capable to contain an eventual explosion, with the only exception of lamps explicitly rated for open fixtures (those usually feature a an additional shroud around the arctube, to absorb the energy of the eventual arctube rupture).
It is true, HPS explosions are unheard of, mainly due to rather low operating pressures (around atmospheric, which someone may say it qualify as a "medium" and not "high" pressure lamp) so when it overheats, the elevated pressure way more likely extinguish the arc than challenge the arctube physical integrity. Plus the arctube volume is very tiny in HPS compare to the other chemistries. So if the arctube breaks there is very little energy in the compressed gas.
However what does happen from time to time is a leak from the arctube to the outer, compromising the vacuum there and so causing the discharge striking between the metal components (holding and connecting the arctube to the lead in wires). This causes then huge stresses in the glass of the outer bulb, which may then shatter and so release the hot fragments out.
The risk is then not that much from the fragments falling from high or low heights, but just from being hot so capable to set something around on fire. Plus the hot sodium coming into contact with air starts burning immediately, so another thing capable to ignite some nasty fire.


I had a questions about the structure of HPS lamps: You mentioned liquid. I understood the arctube to be xenon, sodium, and mercury vapour?

The gases are in the active area (in the arc,...). But there should be something to keep their pressure correct. HPS usually use a reservoir with a liquid Na and Hg mixture maintained at exact temperature so it forms saturated vapor pressures exactly at the level required for the discharge (it is in the same cavity as the discharge, so Pascal's law makes sure the pressure is everywhere the same; only a bit away from the main arc, usually behind electrodes or in a short metal tube stud attached to the end of the arc tube). The temperature is stabilized by an equilibrium of heat transferred by conduction of the arctube wall from the arc, vs the thermal radiation of the reservoir section (proportional to T^4, so the temperature does not change much even with some change in heat power). This trick allows to maintain the pressure even when part of the fill gets lost (absorbed into the arctube wall or diffuses out completely,...), plus allows for greater manufacturing tolerances mainly for the fill dose (they put there an excess of the material, then just the needed amount evaporates, the rest remains liquid in the reservoir). But the drawback is, if the heat balance is compromised (e.g. the blackened tube around the electrodes absorbs more heat so runs much hotter, causing way more heat delivered to the reservoir area than originally designed),
the pressure can change significantly, compromising the electrical parameters (hotter reservoir yields higher pressure and that yield higher arc voltage). And this may alter the real power delivered from the ballast (a constant current ballast delivers higher power once the load voltage increases), forming a positive feedback, which if too strong, may lead to thermal instability and so runaway. Because the ballast is able to maintain the arc only up to come arc voltage, usually the arc extinguish. And to restrike, the pressure, so temperature has to drop significantly, which needs some time, hence the cycling.
And because of the required temperature, the Hg/Na amalgam is just melted liquid during normal operation.
The Xe or other noble gasses (often Ne and Ar are used) are there mainly to have something for the arc to form when the thing is cold, so all metals condensed and solid in the reservoir. It needs the heat from this arc to melt the metals and evaporate them before they can act in the arc - that is all the color and brightness evolution as the lamp is warming up after ignition (first only the noble gasses can glow, then the Hg starts to evaporate, only then the Na starts to evaporate and builds up the pressure).



Also when you said they blacken causing them to run hot, is this blackening on the inside or outside of the arctube?

It comes from two causes: One is the sputtered electrode material (tungsten) onto the inner surface of the tube around the electrodes (black coating inside of the arc tube near the tube ends). Because the tube is so thin, this uses to affect only short sections (however the most sensitive ones for maintaining the reservoir temperature balance). This is gradual process from a new lamp till the EOL.
Other mechanism is the fill material (namely Na) diffusing into the arctube wall. This happens in the hottest sections, so around the center of the arc tube. Because this is extremely temperature sensitive, it usually happens only at the lamp nearing its EOL, when it is running hottest (due to the thermal balance effects).
When the outer bulb becomes dark (well, the mirrory patch near the base does not count, that is the getter cleaning the vacuum in the outer and is designed to be there), usually it means the Na had leaked from the arctube and reacted with the glass (the hot glass behaves like an acid, recting promptly with Na, forming dark brown opaque stain).


If we just consider HPS bulbs (and not MH) I had 4 possible ideas on how to move forward:

1) Find a place that has lots of spent bulbs and pick out the ones that cycle and use these. When bulbs get the phase in their life of cycling, do they remain in this cycling phase indefinitely? Or for days, months, years, before they stop lighting altogether?

Nothing guaranteed. Some leak the arctube after few cycles, some remain cycling for years.


2) Modify or have manufactured bulbs that will cycle from the start. Could this be done by 'blackening' (painting?) the arctube in some way (if its on the outside) before it's place in the outer vacuum glass bulb? I read that the loss of sodium escaping the arctube is an issue? Is there any truth in that? Perhaps there are people who custom make lightbulbs, if there is physical make-up that would incite cycling, i.e. less sodium vapour in the mix for example?

Can not imagine how to do that and not paying a tons of money. Basically you are asking for a special lamp development. That uses to cost high 100k to Meg $. That is the reason why any specialty lamp is so expensive compare to a mass market type: With the mass market the cost is dilluted to the sheer high production volume (many millions of bulbs) so it becomes nearly nothing, in specialty the volume is low (10000's), so the development is significant part, even when they are kept as close to some mass production type and worse performance (mainly lifetime) is accepted. And you are talking about a dozen pieces or even less. Granted, you probably do not need any life, nor performance, but still only making them would be problematic (it would mean few hours of time on the complete production line)


3) As you say, to over supply the bulb with a higher rated ballast for the bulb. Would there be any danger in this, other than it causing damage to the bulb? If you took a new bulb and gave it too much power, would it cause it to cycle initially?

Yes, there is quite a lot of danger, Overloading the bulb means it will be stressed beyond what was ever anticipated in all safety analysis of the original design. So very high risk of arctube explosion, with consequent spill of hot fragments, burning sodium and boiling toxic mercury.
Plus it is even not guaranteed it would even start to cycle. Many designs are very thermally stable when new, so they can easily run way overheated (the reservoir is a bit away from the arc tube, so even when the arctube is nearly starting to melt, it can still maintain stable pressure).



4) Make a box that would cut power to the bulbs after a minute or so, and then reignite the start up cycle agin and again. Would this accurately display the same visual characteristics as a bulb that actually cycles? It would have the same start up process with the  visual changing colour of light. But does a bulb that cycles, burn brighter and brighter than normal operating brightness before cutting out? Or is a cycling bulb just one that can't sustain itself for a period of time and the brightness never eclipses a normal working bulb?

Many thanks to everyone who can help on this project

This is the only somewhat viable option if the appearance of a cycling bulb is what you actually need.
The cycling pattern varies so much from case to case, nobody would ever notice it. For the warmup effects there is no difference if it is warming up from a cycling lamp or because there was a power interruption.
You may add some random component to the timer (mainly when you will be going 1 minute or longer) and make sure the time varies among multiple bulbs, then nobody could tell the difference vs a genuine EOL cyclers.
In any way count on rather short life when used this way (so keep some spares at hand), but I guess it should not be that big deal.
Safety wise it is the best you may do: If anything gets compromised in the lamp, the eventual structural failure will happen just after ignition, when the lamp is cooled down, so minimum pressures, so very little energy to cause troubles.

And for the control box longevity: Avoid switching the PF compensating capacitors.
So do not wire them into the lanterns alone, but put just one (corresponding to the number of lamps lit at once by the sequencer) and keep it permanently powered (I mean not flashing). These capacitors just do not like to be switched frequently...
As switching elements use inductive load rated triacs with proper snubber RC network (at least VDRs limitting the peak voltages).
You may use relais as well, but you have to use good snubber RC network around their contacts too (prefferably with VDRs).
For ballasts I would choose basic series inductor (I assume 230V area now) and a superimposed ignitor. Do not use semiparallel, as that requires the large PF capacitor on the input very close to the ballast+ignitor (it is part of the primary side pulse current path)
US ballasts should be fine even with integrated ignitors, there the critical loop is just between the ignitor and the ballast winding itself.
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