I started out making a lightbox in Fusion 360, but I ended up making a tealight holder instead. You could of course use any light source you want. I would NOT recommend a burning light inside of this! (I tested it and eventually it gets too hot)

This is a more colorfull version of my model:

Design:

Standard tealight size

NOTE:

• The better you have tuned in your first layer settings, the better this will look. The profile I have included in my model is tested thoroughly and many models got thrown away before I was satisfied. You could print this faster but I think that would compromise on quality
• I would recommend to have a clean bed and a clean nozzle before printing this type of model.

Some important settings I use:

• Layer height - 0.2mm
• First layer line width - 0.34
• Arachne mode ON
• First layer flow ratio 1.02 (if your model comes out with gaps in the front, you could increase this value or calibrate your filament flow)
• Infill wall overlap 25%
• Speed:
  • First layer – 50mm/s
  • First layer infill – 50mm/s
  • Outer wall – 200mm/s
  • Inner wall – 50mm/s
  • Infill/top – 250mm/s