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Years ago, I read someplace that in order to stop a flash deteriorating in storage, every month or so, you should put some batteries in the flash and fire the thing a couple of times.

I'm beginning to think this advice to fire flashes every now and again to prolong their life was perhaps applicable to some older, now-defunct technology and has simply stuck around unquestioned since then becoming part of photography folklore. Or, perhaps it never had any real use at all.

After all, between manufacture and sale, it's not unusual for electrical items to sit unused for many months, possibly years, and no one seems too bothered by that.

And, looking on Wikipedia (albeit with my limited understanding of the science) the main cause of failure of a modern flash tube, beyond the catastrophic, seems to be its overuse.

So, is it really necessary to fire flashes every now and again, or can we just leave them be? If it is necessary, why is it? What's the science behind the idea?

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Flashes have large electrolytic capacitors (sort of a wet variety inside) which when triggered, discharge into the flash tube to power the bright flash. When sitting around turned off for months or years, those capacitors can dry out and fail, or lose capacity. Turning them on causes them to recharge to full voltage, and triggering it a time or two repeats this cycle, which "reforms" them and prolongs their life. So it's not a bad idea to either use them, or to cycle them a time or two at least every several months. When other electronic equipment is stored a long time (radios, stereos, etc), these electrolytic capacitors are a First Concern about the likely suspected failure case if they can no longer "reform".

Overuse can be bad for the flash tube, but using it is good for the electrolytic capacitors. A couple of flashes every several months is Not overuse (but don't leave the batteries in them for long periods).

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    Electrolytics can be reformed without the firing of the discharge tube. So an approach is to charge the unit, and then turn it off, letting the charge dissipate. – mongo Jun 30 at 17:45
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You don't need to fire the flash, only power it on. The short-term energy storage in a flash is the flash capacitor. It has a very high energy density and very high discharge currents. That does not leave a whole lot of leeway for sacrificing performance for durability. The energy in a capacitor is stored in an electric field between two electrodes. The shorter the distance between electrodes, the more energy can be stored. And the more likely there is going to be a breakthrough between electrodes that, at the involved energies, will burn a hole ruining the capacitor.

The electrodes of a capacitor are separated by a dielectricum. Now in an electrolytic capacitor, one electrode is a wrapped metallic foil, the opposite electrode is a liquid (typically drenching some paper-like stuff) and the dielectricum is not explicitly constructed into the capacitor. It is a thin oxidised layer on the metallic foil that is formed by applying and very slowly raising voltage. As the layer grows, the voltage it can withstand grows.

A capacitor that is in use and under its nominal voltage, "self-maintains" its isolation. Not using it causes the layers to deteriorate. The first consequence is leakage, using more battery power while the flash is idle than usual. But if the capacitor has been unpowered for too long, you may get strike-through, burning hole in the foil. Some capacitors are "self-healing" where they only lose capacity but the hole does not result in other consequences. But flash capacitors tend not to have the reserves for this kind of behavior. Once they strike through, you usually have them strike through at the same point again and again.

You have the same effect with old unused electronic music instruments: powering them on may cause their capacitors to explode. Most power supply capacitors in newer years are less critical in that respect.

But flash capacitors don't have a lot of leeway and operate at really high voltages.

Firing the flash is not important. Charging it is. The worst you can do is switch it on and leave it on when the capacitor is already endangered. You start by switching it on very short (so that it cannot reach full voltage) then let the voltage decline again. Do that for a few days before keeping it powered up for more than a minute. After a few weeks of that, keeping it on for longer times may be dared.

And yes, I have several fatally unused flash capacitors in my gear history.

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  • Very surprising that this is debated, but once is a partial reforming (with greater leakage), and all the manufacturers say to flash them several times every several months. A few flashes isn't going to hurt the gear, and I'm flashing mine a few times. Here is a Strobist article:strobist.blogspot.com/2013/06/… – WayneF Jun 30 at 22:02
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    @WayneF "A few flashes isn't going to hurt the gear,": reference needed. Flashing does not help with capacitor reforming and it causes high impulse load. It's (obviously) not going to harm a well-maintained flash, but when we are talking about a long-neglected capacitor on the edge of breakthrough, giving it an additional kick while it is close to failure is not going to help. – user92750 Jun 30 at 22:22
  • If it's your flash, do as you wish. But all of the legitimate advice is to flash it a few times (and observe a small cooling time between full power flashes). Flashing causes multiple recharges which aid more complete reforming which lasts longer. The real danger is too many years of no power, when turning them on then is risking near total leakage which can cause significant damage. The Nikon manual says "Take the SB-910 out once a month, insert the batteries and fire the unit several times to refresh the capacitor." (page H-5) – WayneF Jun 30 at 22:35
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    "Risking near total leakage which can cause significant damage" applies for power supply capacitors, not flash capacitors. If you have near total leakage, the charge circuit will whine and not get the capacitor charged to nominal voltage. That is almost the best case for reforming. A power supply capacitor tends to be connected to a voltage source with low internal resistance: leakage causes high operating currents. In contrast, a flash capacitor is connected to a current source with high internal resistance: operating current is limited, high leakage causes low operating voltage. – user92750 Jun 30 at 23:32
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    The flashing is for discharging the cap so it can be brought to voltage again by the inverter. But yes, it stresses the cap. – rackandboneman Jul 1 at 1:13

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