This is parabollic enclosure for tritium glowstick to make the light more directed and intense.
You will get more light than with simple glowstick enclosure.
Pause it on top of internal cavity, insert glowstick, fill it with rubbery transparent glue, unpause to print it over. cover the curved side with aluminium foil.
i used "Betalight Tritium Self Illumination Grow Marker Isotope 3.5mm 25mm Green 1pc" from Ebay - US $15.50
PROTIP: print with transparent material or glow in the dark.
I used PETG trnasparent.
insert pause to top layer of the cavity or pause it yourself to insert the glow stick.
fill it with rubbery transparentglue to dampen impacts
glue the curved part (and sides) with reflective material like aluminium foil, polish the flat side (if you don't have a PEI on the bed) and drill a hole for keyring.