This is a simple clip to attach to a generic nightlight that you can find in most dollar stores. For creating the lithophane. I use 3dp.rocks and choose the Outer Curve sized to 100 mm:

https://3dp.rocks/lithophane/

Import the nightlight clip into Blender. Then import the lithophane, size it properly and align it with the front edge of the clip. Export the whole thing as an STL.