In early 2023 Daisy passed me an enquiry from a smallish regional bank in southern Brazil. They wanted around 140 UV torches, one for each teller window across their branches, to check notes. Not a huge order by volume but a tidy repeat customer if we got it right.
They had ordered 395nm torches from someone else the year before and the tellers basically stopped using them. The complaint was that under the torch the real notes and the fakes looked too similar, just a general purple haze. Classic case of the wrong wavelength, which I wrote about before.
So we sent 365nm samples with the filter glass. Better, but then a new problem, the Brazilian real has security features that fluoresce in specific colours, and the tellers needed to see them quickly under bright branch lighting, not in a dark room. A weak 365 torch under fluorescent ceiling lights is hard to read.
We ended up bumping the LED drive current a little and tightening the beam so the spot was more concentrated on the note. Daisy went back and forth with their security officer maybe a dozen times over six weeks. She is patient in a way I am not.
The detail that mattered most in the end was boring, the switch. Tellers wear gloves sometimes and they want a torch that turns on the instant they grab it and off when they let go, momentary style, not a click-on-click-off that gets left burning all shift. We changed the tail switch for them.
Funny thing, half of getting that order right had nothing to do with ultraviolet at all. It was switch feel, beam width and runtime. The physics was the easy part.
They reordered twice since, last one was 95 units after a branch expansion. And now whenever a bank or a casino enquires I ask about their lighting and whether the staff wear gloves before I even talk wavelength. Learned that from Brazil.
