I just got interested because after handling some spice my fingers were glowing under uv light Just wanted to make sure that it was not -even if unlikely- some lye residue.

I did shine my uv light on the nearly 99% lye and it does not glow. But something different happens def. You can see tiny sparks of light or somethings wandering up from the lye. They appear under the uv light. What would that be ?

could be any number of things.
lye does not glow under a blacklight, but a lot of different molecules which have double-bonds do. the color and intensity of glow is dependent on the number of double-bonds and structure.