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'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 order them in 100+.
If you do the build 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.
Step 2: The Artwork
You will probably want to print some sort of icon for the switch (around 20mm in diameter) towards one end of the card - mine looks like a light bulb. This is really just a part of the card which will be pushed to turn it on (you will see later how this works - it will align with the battery which is in a circular cutout in the foam behind this).
Then print them out, and cut them roughly around the border (they should still be over-sized). Depending on your inkjet, you might want to spray a clear protective inkjet varnish over the printout before the next step if you want them to be really long-lasting.
Step 3: Sticking It Together
Step 4: The Foam Insert
Now you'll need to stick the foam onto the card - I used two strips of special high-strength double-sided tape, but for most people a glue gun will be a better choice. It works best just putting adhesive along the two long edges I've found. If you've designed your card with a picture of a button on it like mine, you'll want to make sure the cutout hole is behind the printed button!
Step 5: Put in the Battery
Step 6: Attach the LED
Now push one leg underneath the cell (will go between the card and foam), and the other leg should go above the cell.
If you have done it correct, when you press down on the leg which is on top of the cell, the LED should glow purple.
If it doesn't glow at all, pull it out, rotate it 180 degrees (so the opposite leg is on the bottom), and put it back in.
If it glows all the time (without pushing), you will need to pull it out, spread the legs further apart, and put it back in again.
Step 7: Complete the Other Side
Step 8: Have Fun!
If you didn't see some of the fun pictures in the Introduction to the instructable have another look now for ideas ... here are a few things to try:
- Look at foreign bank notes, passports, drivers licenses - even a 2nd class (UK) stamp has a hidden mark on it. Tonic water fluoresces (only slightly), credit cards are great as well and usually have a couple of secret marks on.
- Draw on something with a highlighter pen (yellow and orange works best I think) and then look at it under the UV torch. I like to draw a picture of a skeleton on the back of my hand with a yellow highlighter when I'm doing workshops - the kids love this.
- If you've got anything that glows in the dark, you'll be able to energise it with the torch (make it glow). If you hold it really close (with the LED touching it, you will probably be able to 'draw' with light!
- Get yourself a UV pen to security mark your valuable at home or just to write messages in invisible ink. If you do want to use this for secret messages, it works great on the back of one of the blank PVC cards. Standard paper has whiteners added that make it hard to see the message - you might have more luck with brown paper.
- When it is really dark, go hunting in your bathroom to see how well it is being cleaned ... certain bodily fluids (like urine) fluoresce under UV light.
- One activity which is really fun is to see how well you wash your hands. You can get a cream that you rub onto your hands before washing them (http://www.glitterbug.com). Anything left afterwards (and there will probably be a surprising amount) will glow strongly.
- Some types of bacteria glow under UV light, although you will probably need to culture them properly in a petri dish as small quantities on surfaces, etc will not fluoresce.
- Theoretically you could also find many types of scorpions with this light, as they fluoresce as well!