FR4 is a great material for playing with shapes and LED light. In areas where the copper layer has been removed, it is transparent and, combined with LED backlighting, can produce stunning results, especially in dark environments.

Before etching, don't forget to protect the copper parts on the edges, where you have to solder it to other parts, to build an enclosure. This process is explained at
https://hackaday.com/2015/06/03/how-to-build-beautiful-enclosures-from-fr4-aka-pcbs/

Images show several examples. Every one contains a controller with a light sensor, used not to blink LEDs, but to adjust the light intensity against the ambient light.

Note: for best results, thin (~0.5 mm) FR4 should be used if translucency is required.