Why is the lifespan of metal halides reduced to half when burned horizontal? « on: October 13, 2023, 09:51:19 AM » Author: Robotjulep
I have noticed that most of my probe start metal halide lamps have a 10,000h rating when burning VERTICAL and only a 6000h rating when HORIZONTAL. Also the lumens are higher when vertical. Why is does it shorten the life of the lamp when burned horizontal as well as decrease the lumens?
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	Re: Why is the lifespan of metal halides reduced to half when burned horizontal? « Reply #1 on: October 13, 2023, 10:35:02 AM » Author: AngryHorse
A horizontal arc, (bowing upward), will start to dilapidated the discharge tube walls quicker, plus the halides are directly beneath the arc core and not in a cooler spot around the electrodes when horizontal?, that’s how I have always understood it anyway?
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	Re: Why is the lifespan of metal halides reduced to half when burned horizontal? « Reply #2 on: October 13, 2023, 10:38:14 AM » Author: Robotjulep
Is the arc affected by gravity?
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	Re: Why is the lifespan of metal halides reduced to half when burned horizontal? « Reply #3 on: October 13, 2023, 11:24:04 AM » Author: Medved
In fact yes. To be exact not the arc irself, but the gravity is what pushes denser, colder gasses underneath the hotter, less dense ones. So it is the force behind the convection currents within the arctube. Because the main heat source within the arc tube is the arc, it causes the convection currents to blow upwards at the place of the arc itself, hence blowing it upwards. When the lamp is burning horizontally, the arc bowing upwards, it becomes nearly licking the quartz just above it, so causes it to operate at way higher temperature, so degrading faster.
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	Re: Why is the lifespan of metal halides reduced to half when burned horizontal? « Reply #4 on: October 13, 2023, 09:16:19 PM » Author: Robotjulep
That makes sense. That is probably why horizontal shoebox parking lot lights need to be re-lamped way more often than high bay lights. Really the 10,000 or 15,000hr ratings are only if burned vertical.
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	Re: Why is the lifespan of metal halides reduced to half when burned horizontal? « Reply #5 on: November 01, 2023, 02:16:24 PM » Author: Robotjulep
But what about the probe-start hydroponic grow light metal halide bulbs such as 1000w m47? Can those last long when burned horizontally when they are rated for horizontal burn only? This also begs the question: Do base-up only metal halide bulbs last much longer than universal burn metal halides when both are burned base-up? It gets kinda confusing here. Why are there specific burn positions for metal halides if all of them could just be universal in the first place? If this is the case, I think I will get a hydroponic 1000w grow light metal halide rated for universal burn for my Cooper Lighting Lumark 1000w flood instead of using the universal-burn GTE lamp.
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	Re: Why is the lifespan of metal halides reduced to half when burned horizontal? « Reply #7 on: November 01, 2023, 08:29:47 PM » Author: Robotjulep
Does it mean some quartz metal halide lamps last long when burned horizontally? For instance, the tubular MH lamps. I see them used often in horizontal-burn fixtures such as the Sylvania Syflood or in grow lighting. Can grow light metal halide lamps intended for digital ballasts operate well on their magnetic counterparts? Sorry if I am asking too many questions at once.
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	Re: Why is the lifespan of metal halides reduced to half when burned horizontal? « Reply #8 on: November 02, 2023, 02:56:43 AM » Author: Medved
The "last longer" is not that simple. The thing is, the life od the lamp ends, once one of its critical components fail. So far the discussion was just about what happens in the arc tube and it is what dictate the life of universal position rated lamps, but there are other components too, mainly you have the outer bulb, you have the socket attachment on the glass bulb and e.g. the temperature it can withstand, you have the socket within the fixture and the temperature it can withstand... You may have a perfectly fine arctube, but when the outer cracks, or the socket detaches, you get a lamp EOL. The thing is, some position stresses some parts of the bulb, other stresses other ones while the first part operating at a too low temperature poses a performance burden. The art of designing lamps is to balance everything for the desired use. So if you design a lamp that is expected to be used only horizontally (like e.g. a grow lamp), you will likely optimize the burner so the arc is not overheating it yet the coldest spots do not affect the performance that much, you may e.g. make the outer larger in diameter to be further away above the arctube, but you may design the lamp way shorter than a BU one, as the socket won't be exposed to the rising hot air. But once you run such lamp BU, the socket may overheat and kill the lamp, as well as the fixture (the maximum permissible socket temperature is standardized, but a HOR lamp may be designed to approach that already in the horizontal position, so exceed it in the BU one). So the fact a typical universal burn lamp uses to have the longest life when BU, does not automatically  mean a HOR lamp will like the BU position at all. You may get quite a nasty surprise there...
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	Re: Why is the lifespan of metal halides reduced to half when burned horizontal? « Reply #10 on: January 01, 2024, 03:09:14 PM » Author: WorldwideHIDCollectorUSA
I have also been under the impression that magnetic arc deflectors such as the ones used in early mercury vapor fixtures designed for horizontal burning medium pressure lamps such as the GE Form 109 might help extend the life of horizontal burning “universal burn”, “base up only”, or “base down only” quartz metal halide lamps by using repulsive forces to keep the arc centered and away from the arc tube.
« Last Edit: January 01, 2024, 03:12:32 PM by WorldwideHIDCollectorUSA »		Logged

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	Re: Why is the lifespan of metal halides reduced to half when burned horizontal? « Reply #11 on: January 02, 2024, 01:14:33 AM » Author: icefoglights
They used to make horizontal burning lamps with curved arc tubes.
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	Re: Why is the lifespan of metal halides reduced to half when burned horizontal? « Reply #12 on: January 02, 2024, 01:15:39 AM » Author: WorldwideHIDCollectorUSA
I have a few Sylvanias in my collection.
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	Re: Why is the lifespan of metal halides reduced to half when burned horizontal? « Reply #13 on: February 27, 2024, 07:21:12 PM » Author: 108CAM
This tubular 400w MH Sylvania Metalarc lamp was burned horizontal inside a floodlight that was angled down to work more like a street light and you can clearly see where the heat has taken its toll on the lamp. The lamp was orientated in such a way that the halide salts were allowed to settle along the entire left side of the tube which was facing down. This has also caused a white cloud to form on the glass directly above the tube due to being subjected to the constant heat of the lamp. The arc tube also looks to have slightly deformed on the right hand side which was facing the top and therefore got the most heat stress.
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	Re: Why is the lifespan of metal halides reduced to half when burned horizontal? « Reply #14 on: February 29, 2024, 03:06:09 PM » Author: Robotjulep
Does it still work?
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