Did six backlit signs before I got one I was happy with. What went wrong:
1. Engraved too deep for edge-lit. For edge-lit acrylic you want a shallow, dense engrave that scatters light — deep grooves just look grey. Low power, high DPI, one pass. Test on a strip first with the LED actually on; it looks completely different lit.
2. Used extruded acrylic. Cast acrylic engraves frosty white and edge-lights beautifully. Extruded goes clear-ish and dull. Cost difference is small, visual difference is enormous.
3. Put the LEDs on the wrong edge. Light enters the sheet from the edge and travels — engrave on the face, light the edge closest to the densest part of the design, and mask the other edges with tape or the light bleeds out and you lose contrast.
Bonus: engrave mirrored on the back face for a sense of depth, then light from the bottom edge. That's the trick behind most of the "how did they do that" signs.
