Trits dim fast because Tritium has a twelve year half life. There are other Beta emitters that have longer half lives. We mostly use Tritium because the others are all more dangerous to have around. Carbon 14 has a half life of 5,730 years, but that still isn't enough for this project.
I have seen pictures of old school Inuit oil lamps. It is an open container, not too different than a shallow cup with a ledge on one side. A wick lays on the ledge with one end down in the seal(?) oil.
Put the whole thing deep under the Moon, either North pole or South.* set up a tunnel pointed at the sun. Someone comes along, unblocks the tunnel, and it lights up an image. That image shows how to change to the next image. If the moon has processed they can see that and dig a new tunnel...
Turbodog, I know that you don't want to run line voltage through the wall of the shelter, that you see it as a safety hazard. What would you think about running 12 volts DC in through the wall? You could have a smart battery tender plugged into the garage somewhere and have a good sized 12...
If you want something a little rougher, it would be perfectly possible to take the battery out of the vehicle, rip out a marker light or headlight with some of the wiring attached*, sit the battery in the cave, strip some insulation off the end of either wire (that can be done with fingernails...
They had a neat concept. The actual production would be technically demanding. I expect that they could not manufacture the product and that the whole enterprise has faded. It's a pity, I would have liked some.
What I believe he was saying is that your diodes will be heat sensitive and will last better if they run cooler, and that having lots of air flow over your heat sink will help cool it which will make the electronics work better. For whichever light you choose, check to see if the cool-white...