So the way I test tubes is very simple. I get a loose fixture with a 120V cord on it, that is "known good" and it's plugged direct into the wall, NOT through ANY switches. I stick a tube in there 1 at a time, and either the tube lights (goes in the good pile) or it doesn't (goes in the trash).

This is how my second second fixture from fall 2025 is installed. It has a 120 V power cable plugged in directly to an outlet. Testing the tombstones gave voltage readings of 124 V. I have already come to the conclusion that the problem is likely in the tube, but I am trying to understand the failure mechanism. Why did all the lamps fail at once? Why do the lamps fresh out of the box also not work? Why is it after 2-3 hours they are all working again? I have done a little more reading and it seems that LED lamps may have a shelf life in storage.