Today I started my own try, I found 2mm thickness plexi (4mm was available too but didn't want to change screws).
I found that engraving with a cutter and cutting like glass, with a little pressure and a little luck, is the best way. Then just a little file work is needed.
To remove the lid inner border I used a hacksaw since using a file took too much time.
As a led I'm tryin' one of these 10mm ultrabright leds
with an aluminium foil on the bottom.
I don't make the led go through (it has a little diffusion angle, less than 20%) but made a half-hole with the drill bit, something like a concave lens.
Now I wonder if, wrapping the led and the plexy with aluminium foil I could maximize the amount of light routed on the border, something like this:
Any scientific explanation is welcome too!