Yeah small tritium vials are great. Betalight is not really practical for this, besides being way expensive. Can you get 11mm tritium spheres there? I have an old light that needs one.

I'm finding it surprising given the huge variety of tiny handheld flashlights available, including dozens of kinds of keychain lights, that there are so few options in the ultralight headlamp space. There are several "obvious right ways" to make a keychain flashlight and all of them are well represented by products. But in headlamps, lots of that space is unpopulated. A lot of headlamps also almost get it right, but then mess it up somehow. That's why I keep dwelling on the topic.