Backlit signs are simple, you can find a ton everywhere. However, I needed to make one quickly and with materials on hand, so I figured out how to do this. Here we go.
Step 1: Materials
-Thin (1/4") plywood or MDF - this forms the face & back. MDF will be smoother, will be easier to cut w/o flaking, and will have no warp. It's also more susceptible to water damage. Painted, that shouldn't matter.
-Small stock wood to form the sides. I think I used 1x3 cheap stuff from home depot. 2-3 inches wide is ideal; this will be the depth of your box.
-Paper, vellum, thin plastic sheet, etc - This forms the diffusive layer that lets the letters show up as glowing white. I used paper out of desperation, but something more durable would be nice here.
-Aluminum foil - used on the inner-back of the sign to reflect light towards the front/letters.
-Lights - I used Ikea under-counter lights glued to the front face, pointing towards the back. These are hot 20w halogens, so they're not ideal for an enclosed box like this. Get 12" CCFL lights used for PC case modding instead.
-Jigsaw with small blade (!).
Step 2: Design the Text
I may have actually created this in GIMP, then saved it as a huge JPG, then used posterazor to cut it up for printing. There's no telling *what* I did! You'll figure it out.
Now that you've gotten your printout, cut it out with a sharp blade. I used a swivel knife - made things a *lot* easier.
Step 3: Cut the Front Face
Here's the detail work. First, lay your template on the thin plywood/MDF and trace all the lines. For a quick shortcut, tape the template down and lightly spray paint over it. Either way, you just want to be able to see your text on the wood so you can cut it out.
Now drill a hole on the inside of each disconnected letter.
Now use your jigsaw with its tiny blade. Put the blade into the hole you drilled earlier. Now start the jigsaw and cut out each letter. This takes practice, take it slow. Err to the inside of each letter - you can cut more out, but if you cut too far to the outside of each letter you're stuck.
When you're done, you should have your plywood with all letters cut out.
Step 4: Sand Face, Then Add Sides
Now you've got all the letters cut out of the face. Give it a quick sand to get rid of jaggies.
Now add the sides. Cut your wood stock to the right lengths (top and bottom, left and right). Remember - only 2 sides will be the same dimensions as the front face. The other 2 will be shorter to fit inside the first two. So if your sign is 4ft, the top and bottom will be 4ft long. But if your sign is 2ft tall, the left and right sides will be 1ft 10 inches (2ft - 2in to account for the top & bottom walls).
Now drill pilot holes and screw the front face to the walls. Also screw the walls to each other. You'll want those pilot holes - everything here is thin and will split easily.
Step 5: Paint
Prime with primer. Then paint with paint.
I used a small detail spray gun ($15 harbor freight special) along with a small compressor (twin stack cylinder kind). Most of the even smaller HVLP spray guns must be driven by a quite large compressor, which I don't have. This one works well for latex (ie. acrylic) paint/enamel. Just thin the paint down with latex extender & water. Water alone may work - haven't tried it.
Do a few layers here. If you're using plywood, the grain will show through even after a few layers. MDF wont have this problem, but will soak up more primer. If you have plywood and don't want grain, use a wood filler/sealer first. You'd have to do a huge skim coat, then sand down. Just use MDF instead.
Step 6: Add Diffuser & Inner Letter Pieces
Cut a few strips that are taller than the letters, and just hot-glue them to the inside surface of the front face. You can spot glue, no need to run huge lines around the whole thing.
Inner Letter Pieces
Cut out the inner parts of the letters in black paper. This is the inside of O's and P's, the upper insides of e's, etc. You can also glue aluminum foil to the back of these letters to make them more opaque. Now tape/glue these to the appropriate spots on the front side of the diffuser.
Your letters no longer have those annoying empty spots.
Step 7: Add Aluminum Foil
Now the back. You have a back the same size as the front (don't you?). Doesn't need to be painted. Get a big strip of aluminum foil, lay it down, and hot glue it in place.
Step 8: Add Lights!
Now it's time to add lights! Glue your ikea halogens to the *front* face of the sign, pointing towards the foil. Why? If you put them right behind your letters, pointing forward, then you'll get hot spots - it'll look like you have a few separate lights pointing forward (which you do).
So you put them on the front, pointing backwards. The foil reflects the light, and the diffuser evens out the light. This creates more even lighting.
Now go back and ignore everything above. Get CCFLs instead (like these from SVC ). Those you can mount directly behind the letters on the back, right on the foil. Those will give more even lighting. They're cooler, cheaper, run on 12v (which you'll need an AC adapter, just grab an old router/laptop/wii adapter). With shipping they came to about $10 each for the 2-packs.
Step 9: Ventilation Holes
Drill holes on the top (and bottom). A bunch is fine. You wont really see these anyway.
Drill a small notch for all wires to exit the box.
Step 10: Add the Back & Light It Up!
Now screw the back face onto the box. You're done with the box itself! Turn it on, and bask in the incredible backlit-ness!
Step 11: Make Hangers
This step I goofed. I wanted this to hang on a pole with a fabric backdrop, which causes problems. The sign is relatively heavy, and if you want it in front of the fabric, it'll hang down at an angle and hit the fabric. That would look bad. I came up with a crazy idea for mounting.
Step 12: Show It Off!
You have some method of hanging it (better than mine, hopefully), and you're at the show with less than a few minute's sleep from a night of building a stupid sign. Now's the chance to show it off!
Hang the sign, drape the wires behind the backdrop, and plug it in. LET THERE BE LIGHT!
Step 13: Post Mortem
After countless hours trying to figure out (and then building) a DIY backlit sign out of simple materials, I've learned a few things.
-Use MDF instead of plywood. It does not flake/splinter, and has a smooth non-grained finish.
-Use the thinnest materials you can to save weight.
-Use CCFLs instead of halogens. More even light, cooler, cheaper. Don't wait until 10 hours before the show to realize you want CCFLs. Most places will not ship that quickly (at 4AM).
-Design better hangers. These are bad, fragile, and bend the thin back. They're ungainly since the hangers are so long.
The entire thing could be done more easily by using lexan for the front face. First, sand (with very fine paper) the inner surface of the lexan to diffuse it. Now cut mirrored/reversed letters out of contact paper, stick them to the inside of the lexan. Then paint the inner face of the lexan. Now remove letters. Much easier than cutting all the letters with a jigsaw. This will save a lot of time, allow you to create more detailed designs, etc. Just make sure your paint really can block all that light, or it'll look bad.
Or even simpler: stick black contact paper to the inside of lexan. Cut out the letters. Remove the letters. Done.
Please comment, critique, and suggest. It's a relatively simple idea, and you may be better off just buying something ready-made. But it's a fun thing, and the end result really does look great.