I need advice on building a UV LED flashlight

Hi all,

My daughter (11 years old) is involved in an activity called Destination Imagination, where groups of kids are given a challenge and have to come up with the solution, including building everything that they might need. Her group is involved in performing a skit with technical aspects. They need to come up with, and build, a gadget that has something to do with optics. There idea is to build a black light flashlight.

Right away, I'm thinking...COOL!!! Then I think of the challenges. Besides the kids having to build this, it also has to be bright enough for the audience to see a blacklight effect in normal lighting levels. What those levels might be, I'm not sure. In past years it's been a stage in an auditorium, and other times it's been in a school classroom.

The other challenge is that it also has to be battery powered. My thoughts immediately went to UV LEDs, but not being a flashlight builder, I'm wondering if this is a project that is feasible.

Having been on this forum off and on through the year, I know there's some torch wizards here. I'm hoping to get some advice...Can this work, and if so, what's the best route to go?

I've even contemplated using a fluorescent UV bulb but I'm not sure if it's possible to build one that's battery powered.

Thanks,
Lenny

Use the Cree UV LED as a basis for the torch. Let them come up with a way to bias it (hint, use current limiting resistor with 3 alkaline cells in series). You can always supply all the material (LED, flashlight host, resistors, etc) and when it's done, you get to keep the torch

I cannot help you with the building of an UV light, but I can provide some good advice on safety. Please make certain that you understand the dangers of UV radiation, and then pass that information on to your daughter and her friends. UV lights and young children can be a dangerous mix. Good luck with the project. Kirk

Howdy friend. I've made a few UV flashlights--first with 5mm leds and resistors, and then replacing luxeons with Cree UV 1W Xlamp 7090s. The Cree has a lot more power, but if you want those extra low wavelengths, you'd have to use 5mms.

If you want to do something simple, check out this post where I put a Cree Xlamp in a 2AA maglight:

https://www.candlepowerforums.com/threads/144003

It's probably the best throwing UV light I've made, due to the magled's deep relfector.

You're going to want to purchase a pair of yellow UV shielding safety glasses. My local harbor freight has them for 3 US dollars, and not only will this protect your eyeballs, but the yellow color helps define what is reflecting dark purple verus what is fluouresing.

Now that I've reread your post--you said you want to see hte fluourescing with ambient lights on---that isn't so feasible. The lights in the room cover everything with gobs of visible light, which will easily wash out any fluourescence. Your kids on stage may be able to see a faint glow, but the audience will not. If you want this to work, you're going to have to kill the lights. Fluourescent UV lights powered by batteries exist, as do line powered ones. I picked up a pretty long tube with light housing from Walmart of all places for 10 dollars. It isn't directional and doesn't shine far, but puts out more overall light than even the one watt cree.

Yeah I have a little flourescent black/white incand combo light that runs on, I think, 2xAA cells... Maybe 4xAA cells. It puts out a very impressive amount of UV, but only really in a generally darkened room.

I got to check out a light using a Cree that a fellow forum member made... I think it was in either a 1xAAA or 1xAA Dorcy housing. That's the only time I played with a Cree. I have a couple 5mm UV lights that I think are 'better' for detecting 'stuff' at short distances, but that Cree is very impressive for throw and if I recall, it made a switched off TV screen glow in a unique manner. But I digress.

So, this light needs to be bright enough that an audience can see the effect from some distance back? If there is very much ambient light, that rules out reasonable 5mm LED-based lights. Maybe one of the 30+ LED Mag conversions might work, but I think your best is flourescent or incandescent.