what is the likely cause of a single fluorescent tube not working in a light fixture with a ballast that supports two tubes?

by Daniel   Last Updated December 06, 2018 09:21 AM

So I've got a warehouse with many fluorescent tube fixtures. We are slowly transitioning piecemeal to LED as we run out of replacement ballasts and bulbs.

I've got a fairly simple troubleshooting technique:

  1. Are both tubes out? Probably the ballast.
  2. Test the fixture with a known-good tube.
  3. If known-good tube works, then the ballast is fine. Replace both tubes.
  4. If the known-good tube doesn't work, the ballast is bad. Replace ballast or retrofit to LED.

  5. Is only one tube out? Then the ballast should be fine (???). Replace the bad tube.

So here's where things are weird. I've got two fixtures now where one tube works, and the other one doesn't. But even when I replace the bad tube with a known-good tube, it doesn't work.

I've checked the wiring and it's fine. On one fixture I even saw the tube "burn out" - and that fixture has been chugging along for years without any intervention. It would be weird for it to suddenly develop a wiring problem out of nowhere.

I guess my question is, is it possible for a ballast that supports two tubes to fail on one tube only? I didn't know this was a failure mode for electronic ballasts. But maybe it is an internal wiring problem...

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