We used acrylic, but you can also use polycarbonate, polypropylene, or a number of other clear plastics. You can cut a piece out of a thick-walled clear plastic container or get material like this at the hardware or hobby store. This clear acrylic came with protective blue film on both sides.
The initial sheet that we had was about 12″ square, and it turns out that this particular material *cannot* be cut with scissors– it cracks and shatters. What does work (for this and other brittle plastics) is to score the material with a sharp hobby knife (along a straight edge) and then quickly snap it to break the material along the score. Using that method, it’s pretty quick to cut an appropriately sized piece of plastic from a larger sheet.
Trace the size of your plastic piece onto a sheet of paper. Then, draw a second rectangle inside the first, leaving about 0.5″ (13 mm) gap.
Make a drawing of what you’ll want on your card front; it should fit well within the inner rectangle on your paper. Once you’ve got a plan, put your plastic piece on top of the drawing and trace the shape into the plastic with the hobby knife.
Obviously, how cool your shape looks will influence how cool the final product looks. This one is just a simple tree pattern– not too tricky. For the snowflake you can print out and trace some real snowflake patterns.
(For these and all other images here, click the pictures if you want to take a closer look.)
For our LED setup, we’re using a classic “LED Throwie” arrangement– an ultrabright LED is attached directly to the leads of a CR2032 lithium coin cell.
When the bright LED is pointed at the edge of the plastic, it travels through cleanly but lights up the areas that we’ve scratched.
So we have the light going into the edge of the plastic. Next we need to (1) hold the LED there and (2) restrict light from going in directions that we don’t want. We can accomplish both of these goals by using black electrical tape to hold the LED in place. We start by putting down a piece of tape, sticky side up, and sticking the plastic plate and the LED to it. Next we add a matching piece of tape on top, forming a tight seal around the LED but keeping it pointing into the plastic.
Next, wrap the other three sides of the plastic plate with black tape to keep them dark. Note that the tape only needs to go over the very edge of the plastic. After finishing that process, the single LED can light up the tree scratched into the plastic without much leakage of light elsewhere.
Next, we need to start the card itself. We used 9 x 12″ heavy bristol cardstock, but other heavy opaque papers will work as well, and the size really isn’t that critical. Fold it in half and in half again to make a classic greeting card shape, 4.5 x 6″ or so.
As shown above, place your completed edge-lit “innards” assembly on top of the folded card to make sure that it’s going to fit okay, and to determine right where you’re going to put it. What we’re going to do next is to cut a window in the front face of the card so that the clear plastic can show through.
In order to cut out the front window, it’s helpful to have a template. Cut out the inner rectangle from your drawing and trace around its perimeter, marking the rectangle that you’ll cut out of the front face. Score the outline with the hobby knife and either carefully cut it out directly with the hobby knife or use scissors to cut to your scored mark. Open up the card to reveal the window from the inside– here is where we’ll attach the edge-lit plastic assembly.
Note 1: In the lower picture, there is some green light spilling out onto the card. You may wish to first put down a layer of black electrical tape at that location to prevent light leakage, since it will probably be visible from the front of the card. (Example here.)
Note 2: We have taped the battery in place, so the card will be “on” until the battery goes dead in a week or so. That’s probably fine if you’re giving this as a gift in person, but not so good if you’re mailing it. But, you can rig it up so that it won’t turn on until it’s received by who ever you are sending it to: Insert a paper strip underneath the battery at this point that will prevent the LED from turning on– use a strip that pokes slightly outside of the card edge, and write “PULL” on the end of the strip.
Our snowflake card, with a blue LED, came out pretty nicely as well. One that we didn’t get around to doing is a snowman card with a white LED. It’s pretty easy to imagine a number of other variations.
One final trick for extra coolness: use two layers. Two independent, stacked edge-lit displays, one with a green LED and one with a red LED:
It’s not easy to capture this with a photo, but the red dots are crisp and clear and float in front of the green of the tree because of the second layer– the 3D effect is really quite wonderful.
(It’s worth noting that this is actually a very old display technique. Stack enough layers and you can even make a side-lit light-guide numeric display clock!)
Making your own edge-lit cards? Please show us pictures in the Evil Mad Science Auxiliary!
Update November 11, 2009: We’ve posted some revisions to this project here.