I bought a cheap LED projector from amazon that boasted a “water effect”, hoping I would be able to hack it for my own purposes, and I was not disappointed.
I picked up a 700mA LED constant-current driver board and some cheap 365nm UV LEDs from China, took out the original RGB LED, soldered a couple of connections to the board where the DC adaptor plugs in, and voilà!
The 365nm LEDs are the best, because most of that light spectrum is really invisible… Unfortunately, the plastic lens material on the LED itself flouresces a cyan color under the powerful UV light, which ruins the effect. To solve this, I glued a broken peice of incandecent blacklight bulb glass over the lens inside the projector. The glass used for these bulbs is called woods’ glass, is deep purple and blocks all but UV and IR light, and the bulbs are much cheaper than fancy photography filters made of the same material, so it worked perfectly for this need.
What you see in the video are small containers of UV-responsive pigment that will be used to color reefs and fish, against my off-white tile floor in the dark. I left the packaging off to the side, because that white paper picks up the UV too, but the wider area it covers better shows the texture of the water effect.
I spread the containers out so you can see the contrast between the UV-reactive materials and non-reactive tile floor, it’s stunning how well these pigments fluoresce, as if the light came from within them.