I use an LED 'black light' to see my white decals on white paper:
Black light decal LED by Edmund, on Flickr
This one is about a foot long and is powered by a 5.5V USB plug.
Black light decal by Edmund, on Flickr
You could get some cheap black light flashlights and extract the LED arrays from them and wire them in your buildings or simply buy the black light LEDs.
https://a.co/d/afNeJHv
You can get black light LED strips and cut them into three-LED segments. These already have the resistor and you can run 12 VDC right into them:
https://a.co/d/eCQL8ZX
Good Luck, Ed
I always thought that "black light" sources produced carefully filtered UV light in the range of 390 to 400 nm, with the 'harmful' UV wavelengths removed. You can get UV diodes in more energetic 'colors' but all you need is to produce the fluorescence in your paints or phosphors.
I note that DeepDream advertises a 'roll' of 300 black-light SMDs, with a wall-wart supply to run them, for under $16 on Amazon. That would give you enough diodes for just about anything involving black light effects on a layout if you performed a little surgery...
Apparently I've scrambled what I'm looking for again. The paints in question are here: https://plaidonline.com/search?searchtext=neon%20black%20light&searchmode=allwords.
Edit: I tried to do some quick searches and come up completely stumped.
There's a difference between a UV LED and a Black Light LED. For instance, I have used UV LEDs in some non-model-railroading applications and still have a few hundred of them. However, none of them are Black Light LEDs.
The answer is yes - LEDs are made in both kinds. As usual, Google is your friend.
are you looking for a UV-LED?
greg - Philadelphia & Reading / Reading
Yet another one for my Forum friends. Does anyone make a bare blacklight LED that one could use in a hobby application? I am working on an interior for an HO scale kitbashed building and one of the items in it will be a 3D printed juke box. I want to paint the neon tubes with some paint that only glows in black light. The only black lights I find are already installed in flashlights and other items. Any suggestions, as usual, would be most welcomed.