Author Topic: Effects of Part-Night Operation on SOX Lamps  (Read 366 times)
John
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Effects of Part-Night Operation on SOX Lamps « on: April 05, 2021, 06:00:24 PM » Author: John
Hi All, I'm interested the consequences of operating SOX lamps on a part-night photocell. Does anyone have any experience with this?

My understanding is that in regular photocell operation the lamp will run on average 12hrs per night with a single start. Contrast to the part-night operation of 6.5hrs average but with two starts (except maybe single starts in the middle of summer?). So by going to part night operation hours are approximately halved, and starts are doubled.

So does the lamp last longer than usual because of the reduced hours, or shorter because of the increased starts? :lps: :-\
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Re: Effects of Part-Night Operation on SOX Lamps « Reply #1 on: April 05, 2021, 06:23:52 PM » Author: sox35
It's hard to say, as how long a lamp will run on a single start with a photocell really depends on how long the hours of darkness are. But certainly it can have an effect on lamp life if you switch them too often, LPS in general is designed for one switching cycle per 24 hours.
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Re: Effects of Part-Night Operation on SOX Lamps « Reply #2 on: April 06, 2021, 07:48:01 AM » Author: AngryHorse
Also depends on who’s lamps your using, the Shaw built SOX would last better than the Philips ones, but if you have a stock of the Hamilton built Osrams they’ll probably go black before the emitter is used from the cathodes anyway!  ;D
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Re: Effects of Part-Night Operation on SOX Lamps « Reply #3 on: April 08, 2021, 04:23:40 AM » Author: lights*plus
From what I've understood every on-off cycle is harmful to HID lamps and this is especially true to SOX or LPS lamps. But I'd like a clarification on this.

So can someone confirm, a doubling of the start cycles would reduce a SOX's life to half?
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Re: Effects of Part-Night Operation on SOX Lamps « Reply #4 on: April 08, 2021, 05:14:49 AM » Author: AngryHorse
I wouldn’t say half, because during summer it will only light once, it would be that time during winter/spring and autumn (fall)/winter that would cause the double switching?
That time where it’s not quite light at 6am, but enough to make the lamp come on, (sometimes for what could be 20 minutes), before it went off again?

Maybe it would be just a quarter of it’s total life you would lose?
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Re: Effects of Part-Night Operation on SOX Lamps « Reply #5 on: April 08, 2021, 08:45:21 AM » Author: sox35
It's just not possible to arrive at a quantitative answer to this one. You can't simply say 'twice the starts, half the life', it all depends on the individual circumstances of each installation. You'll just have to try it and see.
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Ria (aka Rommie) in Aberdeen
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Re: Effects of Part-Night Operation on SOX Lamps « Reply #6 on: April 10, 2021, 03:45:25 AM » Author: monkeyface
I have been said that the more a SOX lamp is being switched the life is being shorted. This because of the construction of the cathodes which differs to the ones of any other HID lamp.
But here as well someone could clarify this and confirm.

What I’ve seen in the past is that our street lights with the combo SOX + MV usually the MV lamp was in part night mode and the SOX did run all the night.
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Re: Effects of Part-Night Operation on SOX Lamps « Reply #7 on: April 10, 2021, 04:44:20 AM » Author: dor123
I didn't know that SOX lamps are more sensitive to starting than other HID lamps. the electrodes of MV, HPS and MH lamps consumes emitter during starting, run-up and hot restrike.
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Re: Effects of Part-Night Operation on SOX Lamps « Reply #8 on: April 10, 2021, 05:11:41 PM » Author: John
Breaking update!!! Here is some interesting information I found in "Electric Discharge Lamps" by John Waymouth:

  • A 40W fluroescent lamp lasts 32,000hrs in continuous operation (page 104)
  • It lasts only 16,000hrs burning 3hrs per start on a rapid start ballast (page 104 & 63)
  • Lifespan is further reduced to only 9,000hrs if the rapid start ballast is changed for an instant start (page 63)

So we can forget about the rapid start results since SOX has no cathode heaters. In the case of the instant start ballast we can see that 3000 starts has shaved 23,000hrs off the lifespan of the lamp. So lamp lifespan is shortened by around 7.7hrs per start.

From the above numbers, one can calculate that on a 12hr per start operation expected lifespan is 19,525hrs or 1627 nights. Double the starts and reduce operation to 6.5hrs/night then the resulting lifespan is 9527hrs or 1466 nights. So life is shorter on part-night operation! :eoled:

Of course this data from 1960's fluorescent lamps is a very loose approximation of a SOX lamp, and I agree with sox35 that the only real answer will come from real life testing. But I think interesting none the less 8)

PS I await important technical comment from Medved :lol:
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sox35
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Re: Effects of Part-Night Operation on SOX Lamps « Reply #9 on: April 10, 2021, 05:20:47 PM » Author: sox35
As I said, it's not a simple equation of double the starts, half the life. It depends very much on individual circumstances, the design of the ballast, how much emitter was applied to the cathodes during manufacture and a whole host of other things. You really do just have to suck it and see. But for my part, it wouldn't be worth the effort. The amount of energy that would be saved has to be set against the reduced life of the lamp, whatever that might be.
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Re: Effects of Part-Night Operation on SOX Lamps « Reply #10 on: April 11, 2021, 12:48:37 PM » Author: Medved
Also the more starts do more starting damage, but half of burning hours per night means the useful life (measured in days of service) gets recovered back to a big extend, sometimes it may actually lead to a longer service life.
So even when the lamp lifetime becomes (hypothetical figures) 18k hours instead of 24k, operating it for 6h/night instead of the 10h/night means the average lamp will last there 8 years (+something) instead of 6.6 years on standard 10h/start photocell.


The emission dose variability is just the normal manufacturing variable, it causes variation of the exact moment of failure for an each individual lamp, but for itself is not that much important.
Important are frequent minima along the production, which result into the 2% failure life being too short, if the installation is to be maintained by scheduled mainenance work (group replacement) schemes.
But has no meaning of whether you should operate a lamp that or the other way. The way to operate should always be steered by the cost of the light calculation (there the cost in money of purchasing the lamps, ballast and electricity is only part of it, other part are things like the environmental impact, the logistic hassle around servicing, the impact of eventual failures, security and reliability of parts supply,...)

But when you have one single lamp, the uncertanity of the production parameters variation may indeed cause way wider life variation than is the difference between the use of full night vs part night photocell.
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Re: Effects of Part-Night Operation on SOX Lamps « Reply #11 on: April 12, 2021, 03:28:48 AM » Author: John
;D ;D ;D

Yes this is true that lifespan of the lamp is only one factor. If the lamp puts light during the hours that light is not wanted, or no light when light is required, then it's not much use really is it.
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