Need UV LED for currency detection

Hello All,

So am using UV LEDS from Radio Shack* Using them, I can see the UV strips on US
currency bills, but not their color. The light does work as I see other hidden items on credit cards, etc.

But I really want to be able to see the COLOR of the strips in the bills.

My research and help from other people suggest that I need to find LEDs with a LOWER wavelength.

Does anyone here know what the PROPER wavelength would be? And are such LEDs available for sale? My online research has found LEDs that are lower wavelngth than the Radio Shack ones, but they come encased in in metal chambers, are $50 a pop, etc.

I have to believe that the answer for what I see is out there. Just can't find it myself with Google.


Many thanks ahead of time for any hints or answers,

Sergio

Radio Shack UV LED data
High visibility, T-1 3/4 (5mm)
Intensity: 280mcd (typical), wavelength: 395nm (minimum), 410nm (maximum)
Viewing angle: 30°
FW current: 20mA; FW supply: 3.2 (typical), 3.8V (maximum)
RoHS compliant

I can see the color of the strip under 365nm and 385nm LED's. Neither one really seems to be better than the other.

This photo was taken under an array of 385nm LED's.


I have no idea what's all over that $20. It doesn't show up under white light.

Kaidomain has a 365nm P60 dropin that cost $15.
It is able to see the color of the currency strip.

- JonK

look for LEDs advertised as 365nm or 385nm. Keep in mind that these specs don't mean that the LED emits only 385nm radiation; rather, the radiation's spectrum is centered on that point, meaning most of the light will be 385nm, but there will also be some shorter and longer wavelengths mixed in. The less of the longer waves and more of the shorter waves, the better, so by moving the center point lower, you have less visible radiation to detract from the fluorescent effect of targets.

Hey Mike S.

You guys were right. I got some low wavelength UV LEDs and I worked. Not as well as your photo however. So am just curious how many LEDS are you using here? Would like to make something that is better than I have and at least works well with ambiance light.

Even in my darkroom (bathroom with door closed) I don't get the brilliance your photo shows. Would like to build something without paying $15 per LED.

Many thanks all,

Sergio

Mike S said:

I can see the color of the strip under 365nm and 385nm LED's. Neither one really seems to be better than the other.

This photo was taken under an array of 385nm LED's.

I have no idea what's all over that $20. It doesn't show up under white light.

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