Which UV light should I buy for testing?

Good distinction on wavelength. Most people just buy any blacklight without knowing the difference.

Yeah, 365nm is honestly the way to go. I see a ton of people picking up those cheap 395nm keychain lights and thinking "close enough" — but trust me, there's a noticeable difference when you're actually trying to verify security features.

With 395nm, you'll catch the basic UV glow on most IDs — the big stuff like the state seal or the border pattern that's supposed to pop. But where it really falls apart is on the finer details — like micro-printed UV text, those tiny fluorescent fibers that are supposed to be scattered randomly, or any layered UV images that only show up under a tighter wavelength. I've had IDs that looked completely blank under 395nm but lit up perfectly under 365nm. Some newer IDs even use UV ink that's specifically tuned to 365nm so 395nm just won't trigger it at all — you'll think the ID is fake when it's actually legit.

If you're troubleshooting and not seeing any UV response, first check whether your light is actually 365nm — a lot of cheap lights advertise "UV" but are actually 395nm with a filter. Also make sure the battery is fresh (these things drain fast) and test against a known-good reference like a passport or a genuine state ID you trust. If that doesn't glow either, your light is probably junk.

Honestly, the fix is pretty simple: return the 395nm and grab a proper 365nm light. You don't need to spend a fortune, but just make sure the listing explicitly states 365nm wavelength and shows the spectral output. To be safe, always carry a backup 365nm — I keep one in my bag and one at my desk. And if you're buying for a group, get a couple to compare against each other, because manufacturing tolerances drift. So bottom line: 365nm is the standard for a reason, and 395nm is really just for making white shirts glow at parties.

These are inexpensive on Amazon. Worth owning one if you are serious about testing quality.