There are lots of ways to go about making LED art, but so far I find it easiest to make a circuit for an array of LEDs, and then place LEDs on the right locations on the array to make an image. In this example I make an 8 by 11 array, and later place LEDs on the array to make a space invader.

The video above shows how you can make the stl file for the LED array in under 13 minutes using a combination of EAGLE, Inkscape, and Blender. If you want to skip to printing the LED array circuit, here is the svg and stl files: 8x11_led_array. You can also use the svg file as a starting point for making your own array with a different size, spacing, ect.

Here are some additional details to explain what I'm doing in the video. For this project I'm using a modified footprint for the 5050 LED package, which is a 5 mm x 5 mm LED, as well as a 2.5 by 5 mm pad. You could actually draw both of these footprints, but I already have them how I want in EAGLE, so I just (a) added them to a schematic in EAGLE, (b) converted the schematic to a board, (c) exported the board as a png image file, (d) imported the image into Inkscape, (e) clicked path -> trace bitmap and path -> break apart to get the individual components. This library has the footprints I used for this step: Multi3D.lbr. To use the library, download it into your EAGLE/lbr directory, and in EAGLE click Library-> Use and choose the Multi3D library. As in the "3D Printed LED Nametag" instructable, I used the image_export script for exporting images from EAGLE to Inkscape.

To make drawing easier in Inkscape first setup the snap-to grid. I followed the directions in this link. Got to file > document properties > grids and create a new rectangular grid. Change the units to be mm and the x and y spacing to be 1 mm. Next tab over to snap in document properties and choose 'always snap' in the snap to grids section. Finally you'll want to play with the settings in the snap controls bar depending on whether you're placing lines or component footprints. If you don't see the snap controls bar,try going to View > Show/Hide > Snap Controls Bar. For me, they show up on the far right of the window.

Next, I made a 2x2 array of LED pads spaced roughly 2 mm apart. I copied and pasted these to create row of 8. I then wired them using the 'Draw Bezier curves and straight lines' tool (shift F6). After drawing one line, I changed the stroke style width to 1 mm. I made this the default by clicking Edit > Preferences > Tools > Pen, then clicking "This tool's own style: Take from selection". Once you wire up two rows, you can copy and paste those rows to create the whole array. After wiring up the pads, my LED array looked like the picture. Finally, I (a) exported it as a jpg to join the lines, (b) reimported it into inkscape, (c) did trace bitmap and exported it as an svg, (d) imported it into blender, (e) resized it and extruded it in the z-direction 1 mm following the same process in the "3D Printed LED Nametag" instructable, (f) exported it as an stl file, (g) imported it into Cura, (h) exported the gcode with the 1 mm nozzle profile settings, and (i) printed it out. We printed it out onto a thin piece of polycarbonate, but poster board or other most hard substrates would work. If you haven't printed with Electrifi Filament before, check out the instructable on 3D printing circuits with Electrifi conductive 3D printing filament.