I bought a GE T8 17w LED replacement tube that claims to work in existing fixtures with electronic ballast.
I suspect the source of my problem is that I failed to follow the instructions (turn off the lights first).
Nonetheless, because I've always replaced fluorescent tubes with the lights on, that's what I did with the new LED tube. It came on for 1 or 2 seconds, then went out and stayed out. Again, without reading the instructions, I removed a different (working) fluorescent tube and inserted the same LED tube. Again, it came on for 1 or 2 seconds. Both fixtures now fail to work with a standard fluorescent tube.
All the other fixtures on the circuit still work.
So have I destroyed the ballasts or something? Do I need to get new direct-wire fixtures or rewire the existing ones to bypass the ballast? And then get direct-wire LED tubes and return the ones I bought?
And did all this happen because I left the switch on?
[Edit] Seems like the problem was my fault for not turning off the lights first, but turns out it was not fatal. After testing the known good fluorescent tube in one of the non-working fixtures, I just left it in place. I turned the lights off for a while and then back on, and the tube lit up. I placed a new fluorescent tube in the other previously non-working fixture, and it also works now. This suggests that the electronic starter/ballast reset itself.