How long is the lifespan of a speed light?

Question

I have noticed there are very good deals for used name brand (e.g. Canon) speed lights. My opinion is that used speed lights are worth considering, because the only components that could realistically fail are:

• The capacitor, and if the flash is charging and firing, it shouldn't be an issue (although you will never know if it fails after a month of buying it). Also, non-use could be a bigger issue for capacitors than use.
• The locking mechanism, if the flash has been subjected to continuous removal and attachment, could degrade, but if you have the possibility to check it, you should be able to notice a faulty locking mechanism

I was reminded that the flash tube could also fail. From Wikipedia, we can see the following failure modes:

• Catastrophic failure
  • Easy to check if it has already failed
• Gradual failure
  • Sputtering: this only decreases the light output
  • Ablation: gives the glass a frosted appearance which should be easy to check

Is there something I'm missing? How long is the lifespan of a speed light? From Wikipedia, I can see that

When operated below 30% of the explosion energy, flashtube lifetime is generally between a few million to tens of millions of flashes.

I can also see that:

At 60% of the explosion energy, the lamp will usually fail in less than a hundred.

...and I assume most flashes are operated below 30% of the explosion energy most of the time (2 stops less than 100% of explosion energy, 1 stop less than 60% of explosion energy, and I believe name brand flashes have the full output below the level that causes it to fail in less than a hundred cycles, so 30% of explosion energy would be less than 1 stop below full output), so I don't see how a flash could easily fail, especially in a manner that would be impossible to detect.

Also, if something fails in a speed light, what would be the component most likely to fail?

Answer 1

If it is a really inexpensive deal (eg $5 to $20, as not uncommonly for non-digital-TTL capable gear)... you buy two and you don't care as long as you can still get a couple thousand to tend thousand pops out of each. Which is very likely given that you can assume the abovementioned "few millions" close to the truth.

It is statistically unlikely that you will buy a flashgun with exactly 1% of tube life still left in it.

The main causes of unserviceability in old, used flashguns tend to be ill-maintained battery compartments that got flooded with battery acid (usually can be fixed, if there has been no acid migration into the electronics proper) and worn, aged or ill-maintained capacitors.

There is a good reason that there is no need to assume that the regimen in any speedlite is even close to "60% of explosion energy": Electrolytic capacitors, as are used in flashguns, are very loosely toleranced towards the positive (+20% capacitance is found in a datasheet of a well known maker, for their photoflash products. Some brand might be +50%!). Something designed to be even at 50% would suddenly find itself at 60% that way occasionally, and very quickly fail if used in full-power manual mode.

A brand name flashgun only good for a few hundred cycles would quickly put the maker in disrepute.

If a previous user used a flash to the point of serious thermal stress, that will usually be evident as discoloration/melting/... of the clear plastic diffuser.

Answer 2

You already say:

The capacitor, and if the flash is charging and firing, it shouldn't be an issue (although you will never know if it fails after a month of buying it). Also, non-use could be a bigger issue for capacitors than use.

You are presumably wanting to make a bargain, so you are not likely to buy a flash gun that people replace with a better one. So chances are that people are selling it because after years of having it sit in the drawer, they decided that they don't need it.

So you power it up without flashing it (because you don't want to stress it right away) and after 5 minutes of being under high voltage, the capacitor breaks through because of not having been under voltage for too long. Been there, done that.

Power it on for a few seconds, switch it off again, let it rest for an hour. Pray, rinse, repeat. It's not the discharge that pops the capacitor (though it is an additional jolt), it is the high voltage, in connection with a dearth of isolating surface layer due to not being under power (which reforms the isolating layers eventually) for too long.