This is one of the topics I am intensely interested in: colour changes or intensity changes when comparing banknotes under UVA (365nm) or UVC (254nm).
UVA is what a shopkeeper or a home collector would routinely check notes with, as it is not so damaging if you happen to illuminate your own hand.
I use a Lumenshooter S5 light which is quite pricey, around 90 Pounds. But I get good pictures with a camera on a tripod. Have a look at this nice Fiji note, the 88 Cents.
To get UVC, you need to get a light that outputs at 254nm, but this is not a safe light to just shine around without care!
They use 254nm (UVC) lights as sterilizing bulbs in pond filters.
You can get a mains-powered UVC light but it will emit a pale blue visible light also. You need to filter that light out by using a piece of glass known as a UV bandpass filter. They are quite expensive, the glass is about £30 on eBay.
But, now you have the opportunity to see a big difference between fluorescence at UVA and UVC.
I have a thread on this with a lot of examples on Numista:
[Скрытый текст]
The Czech 1988 20 Korun is the earliest example I have in my collection, currently. Under UVC red blocks appear.
I've seen different UVA and UVC luminescence on many banknotes. Here's an example from my thread about Kyrgyz banknotes – on many, the security strip behaves differently, and the inscription appears in one range. I didn't want to overload [Скрытый текст] with different ranges, as in many cases, the differences are only in the security strip's behavior.
I can't always confidently determine whether the difference in UVA/UVC luminescence was intended by the manufacturer or whether it's simply a random behavior of the phosphors. But when I see a clear difference, I make a note of it (as in the example with Kyrgyz banknotes).
Another interesting observation is the 1995 Bank of Russia notes. The banknotes contain an element that, in addition to glowing under UV light, also has anti-Stokes properties. Various publications for bank employees describe this element's glow under UV light as "pink," but under UVA I see a green glow with small specks. Under UVC, however, I can definitely see pink.
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