UV lamp types — which one to buy

Got asked three times this month which UV light to buy for ID inspection. Here is a clear answer based on what I have actually tested.

The 395nm problem

The most commonly sold UV flashlights emit at 395nm and produce a visible purple glow alongside the UV. This visible component floods the card surface with ambient purple light, washing out the specific colors that UV-reactive security features should produce. The result is that features appear muddier and less distinct than they actually are. You can see that UV features exist but cannot accurately assess their color or contrast.

365nm — the right choice

365nm UV produces minimal visible light. Under a 365nm light in a darkened room, the card background appears nearly black while UV-reactive elements appear as their true emission color — typically blue-white, green, or yellow depending on the ink formulation. The contrast is dramatically higher than 395nm and makes both the presence and accuracy of UV features clearly assessable.

What to look for when buying

Flashlight listings often conflate 365nm and 395nm or use the term "UV" without specifying wavelength. Look for listings that explicitly state "365nm" and provide the LED model number (common ones: NVSU233A by Nichia, LED-ENGIN LZ1, or similar dedicated UV LEDs). Lights sold for currency verification, forensic use, or with "professional UV" labeling tend to use genuine 365nm emitters.

Output power matters too. For ID inspection, 1 to 3 watts is sufficient. The Convoy S2+ UV flashlight with a 365nm LED is a well-regarded choice under $30. XeCon and Nitecore also produce reliable 365nm options in the $25 to $50 range.

How to verify wavelength after purchase

Hold the light over a white piece of paper in a dark room. A 365nm light makes the paper glow bright blue-white (from optical brighteners in paper). A 395nm light makes the same paper glow faintly purple. If you see significant purple, the light is 395nm regardless of what the listing said.