I was asked by a friend to create something memorising his dog that recently passed away.
My first thought was that it needed to be special and in this form unusual.
The idea for an illuminated night / image light was born.

What you need:
3D printer or access to one.
LED strip and controller, size and color of your choice, just make sure the strip is the standard 8mm wide.
12V power supply or wall wart.
As an alternative without the controller use a 9V power supply as you don't really want full brigthness.
Basic soldering skills and the tools for it.

How to:
Go to 3DPROCKS and convert your image of choice to a lithopane of 100mm and with a thickness of 6mm.
You can check and adjust some settings but make sure to stick to the 100mm/6mm.
Download the light box and print it together with your lithopane image.

Light Box by Downunder35m on Sketchfab

Getting it together:
The tolerances are quite tight, so it requires a properly calibrated printer or some sanding on the edges of the lithopane.
Start by soldering the LED strips together after trimming them to length to fit into the prepared grooves of the light box.
You need one section each on the top and bottom and two section for the sides.
You can either use thin wires and solder before gluing them in or if you have a steady hand after they are glued in.
Connect all positive connections with the positive of the LED controller, same story for the negative wires - that is why there is a hole to feed the wires in.

Connect the 12V power supply - you can use the pre-made connectors or solder.

Test if all LED's work as they should and if so press the image into the box - the little posts in the edges will prevent it from being pushed in all the way and keep it level.
Enjoy a beautiful light with a very special difference.

I only had a tiny image of 36kb to work with, proper hi-res images will have a much better look.

This is why there those "shades" in the image, it is the blocks from the original :(

Ok, how does it actually work?
The image is transformed into a grey scale image.
The darker a pixel is the thicker the layer height for the pixel in the print.
As a result the bright parts of the image are very thin and the dark parts quite thick.
With increased thickness the plastic lets less light go through and the image looks like a 3D photo in shades of grey (or the color you printed it in).

Step 1: Little Tipps and Hints to Get It Right

I had a 3mm border added to the lithopane as otherwise the top left corner would have been too thin and brittle.
But as it turned out having this border actually helps to get a much more even look.

The quality of the lithopane will depend on the material you print with.
For example I used white PLA to get a "BW" image of the dog.
Other colors work the same way just that you will get the shades based on your color.

If you only want the image to be illuminated you can print the light box in black but don't use black for the lithopane ;)

As said, the tolerances are quite tight so that no glue is needed to keep the image in the frame.
A bit of force is required to get it in but if it won't budge sand the corners a bit off.

The LED controller is optional, you can use a 9V power supply to get the light level about right without using a resistor or controller - but a 9V battery won't work for long (before you ask).

You can exchange the images if you like, but for the ease of doing so you might want to add another hole in the back of the light box so you push the lithopane out.