The most important thing I learned with this project is, that not all rubber duckies are created equal.

The project started with a rubber duck that was gifted to me by an unknown person at Toorcamp. It has a wingspan of 34mm and strongly fluoresce when illuminated by blacklight (UV-A, or long-wave UV).

As I didn't know the source of my only rubber duck, I trawled AliExpress for similar looking specimen and ordered 50 of them. These turned out to have a wingspan of 37mm, and aren't fluorescing as well as the original. On the upside, the AliExpress ducks are made of thicker plastic and look better than the original when lit up with an RGB LED.

Still in search of the perfect UV-excited rubber duck, I turned to Amazon. After a deep taxonomical study of  beak colors, eyelashes and head shapes, I ordered 50 more. Well, turns out these have a wing span of 40mm, and their lips are more orange than in the pictures. But at least the Bezos ducks fluoresce almost as good as my OG duck when shoving a UV LED up their hole.

To my relief, the hole size of all my samples is 5mm, in compliance with DIN (duck industry norm). So I now have 100 rubber duckies awaiting their fate as SAO ornaments.