It's a simple ultraviolet torch, but the basic design can easily be made as a normal (white) flashlight instead, and the components only cost a couple of dollars. I designed it originally for the Science Museum in London as an interactive workshop for kids, but the adults liked them as much as the children so I decided to keep the design as a business card. It's a great way of advertising that you see things in a different light, particularly if you are involved in science, technology or a creative field. If you're into making things, you might even want to give it away as a kit that recipient makes themselves.
The plain white version is also great and makes a very useful addition to somebody's wallet that they will probably not want to throw away. The second image is a picture of a 'morse code' version as suggested by Johenix in the comments below (thanks for the great idea!).
There are lots of really fun things you can look at with UV light and the pictures above show a few of them - looking at invisible marks on things like bank notes, passports, and driving licenses, testing out how well you really wash your hands, making things glow in the dark (the "Hi!" message was 'drawn' on glow in the dark material), making yellow highlighter ink fluoresce (the skeleton on the hand), investigating certain bacteria, and writing in invisible ink - more about these on the last step of the instructable. You can even go scorpion hunting (not recommended!) as they fluoresce under UV light.
I'll show you how to build them from scratch, but am also providing a complete kit for those that just want a small quantity, prefer an easier build or want to have them supplied pre-made.
I'm also going to publish this instructable at the same time as an educational version with a simpler build, and more details of how to use it in teaching.
Step 1: What you'll need
- A couple of blank PVC ID cards
- A 3mm ultraviolet LED
- Some 5mm (or 1/4") thick foam of some sort that squishes and returns to shape again
- 1 x CR2032 lithium battery
- If you want your own design on the front, you'll also need some way of printing on it. I used some inkjet compatible white self-adhesive vinyl.
I've put together a few links below of suggested suppliers and parts - with postage costs and minimum quantities you're probably looking at $2-$3 each if you wanted to make 100. As I order thousands for the workshops I'm running, a couple of people have asked me if I can supply the bits, which I'm more than happy to (works out around $1.50 each (for quantities 10+) with everything you need, including the foam already laser cut, white or UV LEDs, cards, batteries and self-adhesive inkjet transfers.
UPDATE: Due to the interest I have setup a little web store to sell these kits cheaply: www.flashlightcards.com
If you prefer to buy all the bits yourself, this is what you'll need:
- ID Cards: http://www.smartcardsupply.com/Content/Cards/cards.htm - the cheapest blank ones here work out at about 15c each in packs of 100 and you'll need two for each card. These are pretty standard world-wide.
- CR2032 Batteries: http://search.digikey.com/us/en/products/CR2032/P189-ND/31939 - these ones are 28c each
- 3mm UV LEDs: http://search.digikey.com/us/en/products/UV5TZ-395-30/492-1321-ND/2407229 - about $1 each if you get 25 or more. Something from 390nm to 405nm works OK but the lower the wavelength the better.
- Foam: http://mdbuyinggroup.com/products/podiatrist-wholesale/plastazote%C2%AE-14-medium - about $11 which would be enough to make 100. I used 5mm, but 1/4" works as well. There may well be cheaper foams - type is not crucial as long as it is about this thickness - just needs to be able to be squished and return to its original shape.
- Self-adhesive inkjet vinyl : http://www.texascraft.com/hps/product.php?productid=17514&cat=249&page=1 - about $12 for 10 sheets, but this is enough for 100.