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Telling Apart 365 nm from 395 nm Ultraviolet LEDs and Flashlights

Comparison of fluorescence produced on Canadian bills by 365nm and 390nm UV LEDs. David Prutchi, Ph.D.Today I received an UltraFire WF-502B UV flashlight advertised as emitting at 365 nm.  I was wondering how to tell if it really does, especially since vendors commonly list it as emitting 365-400 nm.

Well, I was in Canada last week, and had $25 Canadian left over in my wallet, so I tried this flashlight and compared it to the fluorescence produced by an Inova X5MT-UVT 400 nm flashlight.  Much to my surprise, the 365 nm UltraFire caused fluorescence that did not show up at all under the Inova 395 nm flashlight.

Spectral response of UG-1 ultraviolet filter.

To make sure that the difference in fluorescence wasn’t due to wash-out by additional white light, I used a UG-1 UV filter (325nm – 385nm bandpass), and obtained the same results.

So there, a $5 Canadian note will make a very useful wavelength-sensitive detector to tell your UV LEDs apart.

Please visit www.diyPhysics.com and www.prutchi.com for other cutting-edge d.i.y. projects, and remember to check out our new d.i.y. Quantum Physics book:

 
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6 Comments  comments 

6 Responses

  1. Paul Spehr

    Hi David

    Excellent way of distinguishing lasers!

    Sorry I missed the book signing!

    Best regards,
    Paul

  2. Dan

    What are the years of these bills? I need to test a new LED from Ebay, and I want to make sure I do it right.

    Thanks. this is the only easy test I could find anywhere on the internet!

    • Good question. I don’t know… spent them on my last trip to Canada. I tried looking for the date on the high-res pictures, but couldn’t find any on the side of the bill that I photographed.

  3. James

    This is the $20 issue of 2004. They stated phasing these $20 bills out in 2012, and I don’t think the newer ones still have that UV printing. However any $5 (issue of 2006) or $10 (issue of 2005) bill should do. They planned to phase these out in November 2013.

  4. Dan

    my $5 says “Issue of 2006” on the front and “printed in 2010” on the back. 🙂 I had to go to a travel agent to get the bill. It fluoresced like your 365nm pictures.

    The seller was “2012topdeal”. FYI

    Thanks!

  5. JFA in Montreal

    I just received a brand new UltraFire WF-502B from DealExtreme.
    The LED has the pcboard silkscreen mask EAST-063

    And it does NOT fluoresce Canadian bills. I have a small F4T5 / BLB fluorescent tube at 365nm and it fluoresce canadian passports and canadian money very brightly.

    My new WV502B does not fluoresce those same items them at all ! It does fluoresce the fabric security thread within the paper in white, but not the fluorescent ink that glows red under 365nm

    So I got a body of the right flashlight, with the wrong LED inside.

    Thank you DealExtreme !