Build a lithophane night light

A photo that only appears when it is lit — and the base that holds it over the lamp.

A lithophane is a photograph you cannot see. Flat on a desk it is a grey slab with a faint texture; held up to a lamp it turns into the picture, because every bright part of the photo was printed thin enough to let light through. It is the most reliably delightful thing a printer does, and it fails in three specific ways that are all avoidable.

Fix the photo before you fix the settings. Contrast is the whole medium — thickness *is* brightness — so a picture with no contrast has nothing to carve. Crop to the subject, push the contrast hard, and prefer a clear subject against a plain background. This matters far more than resolution: an enormous flat photo prints as an enormous flat plaque.

Invert is what separates a carving from a lithophane. Without it, bright areas rise and you get a relief you read by its shadows in ordinary light. With it, dark becomes thick, which is the mapping that blocks light where the photo is dark. The image relief generator does both and the toggle is the only thing separating them.

Base thickness is not somewhere to save material. It is what the highlights print as. Chase contrast by thinning it below about 0.6 mm and the brightest parts of the picture tear during printing, or simply come out as holes, and there is no recovering that from the slicer.

Print it standing up, at 100% infill. Upright means each printed layer carries one row of the picture, which is where the vertical detail comes from; solid infill means no internal honeycomb shows through when it is backlit, which is otherwise the first thing anyone notices. No supports, and slow the first layer down. The plinth prints flat and normally — it is a plinth.

The slot wants about a millimetre of slack. A panel 3.2 mm thick at its deepest goes in a 4 mm slot, not a 3.2 mm one: the two parts are printed on different orientations and a lithophane is too fragile to force. Make the slot as deep as the panel is wide is a step too far in the other direction — 8 to 10 mm of grip is plenty, and a shallower slot means less of the picture is hidden in the base.

Keep the light source in mind while you are still modelling. A USB LED strip or a small puck lamp inside the plinth needs the cable to get out, and it needs the panel to sit a centimetre or so in front of it rather than pressed against it — a point source touching the back of a lithophane shows up as a bright spot in the middle of somebody's face. If you would rather build a proper housing than a plinth, the enclosure generator makes the box and the panel cutout catalogue makes the hole the cable leaves through.

1. Crop your photo tight and raise its contrast in any photo editor first. A flat, evenly-lit picture makes a flat, muddy lithophane at any size, and no setting here recovers it.
2. Open the Generate panel, pick Image relief (under Signs & art), choose the picture, and turn Invert (lithophane) on so dark prints thick.
3. Set Width to about 80 mm — the height follows your photo's proportions — with Base thickness at 0.8 mm and Relief depth around 2.4 mm. Under roughly 0.6 mm of base the highlights tear or print as holes.
4. Add a Box for the stand: 100 × 30 × 25 mm is a comfortable start. It is the plinth the lit panel stands in.
5. Add a second, thin box for the slot — as wide as the panel, about 1 mm thicker than it, and tall enough to reach well into the plinth. Move it into the top face, select the plinth first, then Subtract.
6. Cut a cable exit: search the parts library for a cable gland cutout, or just subtract another thin box out of the back. X-ray tells you the slot and the exit actually meet.
7. Run the print check and export — then print the panel standing upright at 100% infill, and the plinth flat, as two separate prints.