Heh. I'm trying to research these for a concept I came up with after seeing the "time fountain" on hackaday, which is worth a look at (search google). Basicaly, as far as I know there's a few dyes that are water soluble, and they react to UV light, glowing green/red/blue etc. I thought fluroscein was near perfect... however aparently it denatures in sunlight... totaly destroyed in as little as 2 hours! Diagnosis... totaly useless. I hope the buyers of those fountains on ebay new that!
Anyway, i'm calling on those who know anything in the chemistry world, i'm after a water soluble dye which is A) Legal B) Doesn't get rapidly destroyed (but a slow deminish is acceptable) and C) Not highly toxic. Also I'll need to be able to obtain it so nothing that I wouldn't be able to find.
Another thing. With UV led's, do they emit visible light too? It looks like they do on some photo's, but that might just be the camera's ability, and not ours (such as IR can be seen in cameras)

Thanks! If this works out, it'll make a damn good mdp... more details later!

EDIT: Just found this... looks fairly decent. It's in america though, any thoughts? http://www.riskreactor.com/merchant2/merchant.mv?Screen=PROD&Store_Code=RR&Product_Code=IFWB-C0++1+oz&Category_Code=IFWBOZ
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UV LEDs do emit a fair bit of visible purple light.
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Hmm.. well that's slightly annoying...
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I have spent a fair bit of time working with medical grade flurocene salts at work (making laser imaging units for colonoscopes). We made up the flurocene by diluting 100:1 in tap water and kept it on the bench in a clear plastic container. The work instructions say to replace the solution after every use but we found that it could last up to three months (or when things started to grow in it).
These salts are not toxic as they are intended for a patient to drink before they undergo the procedure but they are a bright yellow colour. I can't remember how often we where asked why we keep urine samples on the imaging table.
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Interesting. Perhaps it's just the intensity of sunlight that destroys it. Cool!
This is where my interest in it comes from... http://cre.ations.net/creation/44
Very cool substance! Any idea where it can be bought in small amounts?
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I used to do this sort of thing nearly 20 years ago..
(OK, So I'm an old fart )

When I was in school, I had a part time job repairing and calibrating large-format non-contact ink-jet printers (Jet-A-Mark - They print that big dot-matrix printing on the side of packing containers you see in supermarkets and places - http://www.matthewsmarking.com/products/productPage.php?modelName=DOD%202002A )

To Ink-Jet print on something that can be up to 2 or 3 feet away, they use shaped ruby-crystal nozzles that can be aimed and "focussed" by screwing them in and out. We would set them up on the bench under a triggerd strobe-light and tweak the nozzles until the ink streams were parallel with nicely-shaped tear-droplets at the end of the stream.

We would wind the strobe timing delay in and out and watch the ink-jet coming from the nozzle further and further away until the stream broke up. the idea was to maximise the distance the stream held together for.

Race Car tuners use strobes to watch the action of parts inside engines (particularly springs and things) and no doubt hundreds of other applications..

I once built a widget that hooked the trigger for a 1500 watt (huge !) Xenon strobe light up to one of those "mind machines" that are normally connected to glasses with LEDs that pulse and produce alpha-beta-etc brain-wave frequencies. I gave it to the lighting controller guy to play with the controls while I DJ'ed at a trance party and he was blown away. He swore afterwards he had the crowd pulsing at the twist of a dial nd bought it off me on the spot.

Strobe Lights are amazing things. They can totally change your perception of what "time" is. The guy who built that fountain has just made it all green and UV and funky. Very Artisitic.. Looks great.

I might have to build one after my current project (A Nixie Clock http://www.electricstuff.co.uk/nixiegallery.html )

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Hahah go nixies, i'm interested in those, but lack the time for making a clock.
But guess what the UV reactive stuff is for... clock... Shine UV led's through a membrane of some UV reactive dye... matrix of LED's for time, and some funky patterns if wanted. Would look pretty cool, but the fact you can actualy see UV led's is sort of discouraging the project... arg need to finalise my DT idea! Might pitch the kit robot to the teacher again... thinks it's not a good enough "need".
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You should be able to get some UV-Filtering without too much trouble.

I think - normally people want to *remove* UV, but there might be some UV-Pass stuff out there.
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