This is an instructable on how I made an LED Backlit marquee style letter 'I' for my sons birthday party (and to hang in his room later). Originally I wanted to make a more traditional marquee letter using string lights. But none were available locally and I didn't have time to wait on shipping. I then had the idea of using marbles like lenses in place of light bulbs. Here are the steps I took (including some suggestions on how to do it better).

Step 1: Sign Design

Design was pretty simple (just making one letter). I sketched it on paper then traced it in Illustrator, you can use any CAD or drawing program you want. I drew the letter to scale (23" tall) and tried different colour combinations till I got what I wanted.

I was able to use Illustrators' 'Dashed Line' settings to mark out where my light (marble) holes were going to be. Drawing that path I wanted the lights to be on and then using the 'Dashed Line' settings (You can see the settings I used in the attached image) Illustrator then evenly spaced out the holes on each side. You can then mark the centre of each light with a 'X', something I didn't think of until I had already printed the template. I just did it with a pencil and ruler.

Step 2: Transfer Layout to Material

I used 3/8" good one side plywood for the face of my sign. I taped the printed template to the plywood and used an awl to mark the centre of each light and the corners of the outer cut lines. Then I used a pencil and ruler to draw the outer profile right onto the wood for cutting. You could also use spray glue to stick the template to the plywood and then use the paper itself as a cutting guide. The spray glue method might work better when you have curvy letters like 'S' or 'O' but then you have to get the paper and glue off later...

Step 3: Cut Out the Sign

I then cut out the sign. You can use whatever tool or method you want. I used a sliding mitre saw for the most or it and then a bandsaw for the inside cuts. I then sanded the outer edges smooth with a random orbital sander and some 100 grit paper. I had some splintering or chip-out on the face of my plywood from cutting too fast. I had originally planned to have the wood grain texture show on the final sign but now I had to fill this ugliness in.

Step 4: Drill for the 'Lights'

I had originally intended to use string lights for the sign but couldn't source any in time. I then had the idea of using clear marbles back lit by LED strips instead to get a similar look. I got a bag of cheap glass marbles from the dollar store. I measured a few of them to see what size hole I needed. Glad I did. Some were 1/2" and some were 5/8". I drilled a hole in a test board to sort the different sizes and had just enough for my project out of the bag (less than half). I then did a test to determine which side the marbles should be placed from. In the end I decided to have the bulk of the marble at the back of the sign so that it's lens effect could gather more light (maybe?). I then used a forstner bit in my drill press to drill all the holes.

Step 5: Framing the Edges

I build a frame around the back of the letter to give it some depth, have a place to mount the LED strip and also contain more of the light for the marble lenses to pick up. I bought some plain MDF trim and cut pieces flush with the outside edge on my mitre saw. I worked my way around the edges attaching them with wood glue and brad nails through the face. I then filled the nail holes and plywood edges with drywall compound and sanded it smooth. Luckily I was only dealing with straight sides. If you have to do curves you could try slitting the wood to create a curve or use another material like aluminium or plastic.

Step 6: Paint

I painted the outside red and rubbed some black over top for some weathering. I then used painters tape to mask the edge and used gold flake paint to make a border around the edge.

Step 7: Setting the Marbles and Lights

Before placing the marbles I gave the inside a quick coat of white paint to reflect more of the led light making it brighter. I put a marble in each hole from the back and put a dab of epoxy on the side to glue them in place. Unfortunately the cheap dollar store epoxy too forever to set so I ended up using my hot glue gun to tack the marbles in place. Then I attached the LED strip along the perimeter of the outer edge using it's peel and stick backing. The LED strip I used has separate R-G-B LEDs repeated every 4 inches or so and I was concerned that the colour mixing wouldn't show through the marble lenses if the strip was too close to them (might see some lit green and others lit blue or something) So I mounted the strip as far from the marble lenses as possible. The control box was mounted in the centre of the 'I' and I tucked the IR receiver just under the outer edge of the top cross bar.

NB. After some time the self adhesive backing has come free around the sharp bends of the letter so I've had to reattach the strips with hot glue. You could also use wire staples or thin nails bent over top of the strip (Don't nail through the strip though right?)

Step 8: Wall Mounting

I wanted the sign to float on the wall so that the light would create a silhouette around the perimeter. I cut some wood blocks so that they would stick out from the back by 1/2 inch. I positioned them in the center of the upper and lower parts of the sign in a place where they wouldn't cast any shadows and break the light silhouette. I attached them to the back of the sign with hot glue. I then attached a saw tooth picture frame hanger to the top block. I was hanging it on drywall so I used a plastic wall anchor and screw. Of course with mounting anything your method will vary. The lights are powered by a 12v wall transformer, so there is a wire hanging down the wall from the sign. This is unavoidable unless you want to run on batteries or start fishing wire up the wall.

Step 9: Light It Up!

Then you just need to give the control box 12v and turn it on. While obviously the 'lights' aren't as bright as they would be with an actual bulb or led in each place the colour comes through well. In dim light it looks awesome and the backlit silhouette really makes it stand out. The 1/2 inch spacing off the wall really makes that floating back-glow effect.