This printable ring includes little cut out sections to insert tritium vials - tiny glass tubes containing radioactive gas which glows like a glowstick for decades! They're perfectly safe, but do try not to smash them. A blob of clear nailpolish over the top secures them in place and adds some protection. This ring requires about $20 worth of tritium vials, which can be bought from the-mad-nuclear-scientists on ebay. The dimensions of the vial should be 6mm x 1.5 mm. The inner diameter of this ring is 17mm - you can find ring sizing charts to calculate what that's equivalent to. Scaling up will probably work okay - try to preserve the z height though. If you need to make the ring smaller, you'll need to fiddle around with the file in blender. Partially inspired by the awesome designs of InnovoDesign on etsy.I printed my rings on a Makerbot Replicator 2 using faberdashery plastic, spray painted black. The vials were secured in place with a blob of clear nailpolish. Good print settings on a makerbot-like machine are 3 shells, 0.1mm or lower layer height - no infill required. Print will take about 10 minutes on a makerbot.