Ans don’t forget the tin foil in your hat. Oh, and your underwear.
Wow, lots of responses, this forum never ceases to amaze me! Thanks all! Now that I posted that, and got all these helpful responses, I don’t see any DC visits coming up in the near-term. 
Another random thought: it might not be EMF/EMI, but possibly the noise? The DCs I work in are fairly loud, with all the air-conditioning and servers cranking away. Having a conversation with someone right next to me requires raising my voice quite a bit, borderline shouting.
So if indeed I have some poor solder joints in my lights, the noise-induced vibration might just be enough to trigger the symptoms I’m seeing.
These lights do work fine once they’ve been taken out of the DC. And even in the DC, it’s hit-or-miss: I do get some utility out of my lights, just not the pain-free experience I’d like.
I’ve never taken the time to really see what triggers the issues, though. Usually I’m in a hurry to leave the DC as quickly as possible, so I’m focused on just getting the work done.
In the past, before I had a collection of budget 18650 lights, I just used my smartphone with a “flashlight” app which basically just turns the screen white and cranks the brightness all the way up. Some apps also allow use of the built-in camera flash LED. I haven’t used that scheme in a while, but it always worked well enough. And a cellphone is way more complicated than a flashlight (though there are a lot of similarities: LED lights, microcontrollers, lithium-ion batteries, etc).
I think I’ll start even simpler, and next time I’m there, bring even more flashlights and see if they all have problems or any are exempt from it.
Thanks again everyone!
Armadillo hats work well for blocking, (I wear 'em all the time
), but they don’t work too well for underwear! 
I suggest a flashlight HDS are not cheap but they have their Faraday cage “native” in the flashlight
We used to keep track of what the IBM 1620 was doing by listening to an AM transistor radio.
If the EM radiation there is strong enough to shake, rattle & roll the electronics on a driver that is “shielded” inside an aluminum flashlight body, i would be more concerned about the long-term exposure to it over time on your DNA.
Most of it is now DNB…
if he is there long enough it may become DN (OH)
Yes, always a good start to any problem.
Should be on the front page of BLF
Aluminum foil makes a good Faraday cage, at least for testing. You might put aluminum window screen across the front, but I tend to think it will work without that. I don’t see how a direct drive light could have problems with electromagnetic interference.
Unless its the LED its self, I wonder what would happen if you dedomed and removed the ESD diode (the tiny third wire on the top of the board not touching tie die, I rip them off LED’s I dedome sometimes [on purpose] so I dont have to pick silicone from around them to no ill effects)
I should have done this on “The Day of the Dead”, but I was working.
Did you figure out how to solve your mystery? I, for one, would love to know ” the rest of the story “…
Really, bring more flashlights. Those lost datacenter souls can’t possess ALL your lights at once. The joke’s on them, haha. :bigsmile:
Nope, I haven’t had any reason to go to the datacenter since posting, so no opportunities to test.
However… I briefly used the Convoy S2 in the office recently. This is the one I keep in my back pack, and, as mentioned above, has given me problems in the datacenter.
It mostly worked OK, but seemed unusually dim, kind of like a low battery… I forgot to test the battery at home, so maybe it’s just my perception that’s off.
But now I’m wondering if it’s not the datacenter that is causing the light problems, but something else? I was under the impression that these lithium ion batteries should stay charged for quite a while. All my batteries are (supposedly) higher-quality Sanyo- or Panasonic-branded. And the light in my backpack is practically never used, except in the datacenter. So I would expect to not need to charge the battery very often.
I dunno, at this point I just don’t have enough data. Bringing more flashlights to my next DC visit is the easy way to hopefully collect some more information that might point to an answer.
I’m glad your DC is smoothly cruising.
The LiIon chemistry does self-discharge some, so you can’t just leave batteries in place like you can with Primary Lithiums. I like to rotate my ‘stock’ of 18650s as I go.
Please do keep us “in the loop” as your testing progresses?
Thanks,
Dimbo
custom lead body 
My Crapper auto-flushes whenever a SureFire flashlight is in it's proximity. Not so with Mainland China budget units. I can only conclude that the SureFire is a POS.
it always helps to ask the right question, and that one was awesome…it really woke my brain up