On a lark, I bought one, advertized to have a spectrum at 395 nM. There is a lot of visible light with this unit.
Things that respond well, any thing with daylight optical brighteners; paper, many colored plastics, laundry detergent. Skin, fingernails, dead plant material.
It excites a red fluorescence in my aquarium plants, much less with terresterial plants. It also lights up the aquarium water green, I don't know what that's about. I don't see any effecct with tap water.
I have some of the fluorite spheres that are sold on E-Bay that fluoresce green and continue to glow for hours afterwarde, they respond well to the LED light.
Many of the rocks I find in the Mojave desert have a thin layer of calcite, Mn activated, that glows orange with the normal longwave UV (351 nM, I believe). With the LED light the same areas fluoresce light pink.
Oh, and cat urine. I have cats. Yuck.