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...

  • I have had 1 side failures on electronic ballast most of my ballast are 3 & 4 tube and both have had single sided failures. I have had a few tombstone failures on T5 fixtures because of the heat but not many with T8 /T12 fixtures.
    – Ed Beal
    Dec 6, 2018 at 14:36
  • Mine are all T12 fixtures. I am replacing with LED, but we have a lot of lights and limited budgets. So we are replacing them as they fail. Once we reach a certain amount of failures (where buying in bulk makes sense) then we order a new batch of LEDs. I'm trying to figure out whether to include these two as "failed", and I'm also just curious about if/how ballasts can fail on one side only.
    – Daniel
    Dec 7, 2018 at 14:43

1 Answer 1


I buy most of my ballasts on ebay for a couple of bucks, they are new pulls (seller bought new fixtures and immediately converted to LED). I combine them with the newest 90+ CRI tubes ($2 each) and the light is amazing! Don't look at the fixtures, look at the stuff the fixture is lighting up.

ALL fixtures can take electronic ballasts, I have converted some 1940 era fixtures (after giving them a trip through the paint shop). Those old fixtures are well built. The only exceptions are very cheap fixtures with weird unobtanium tombstones or no space to fit a ballast.

If the ballast is instant start, it is possible for an electronics failure to take out one side. But it's more likely a tombstone problem (or wiring). A bag of spare tombstones (60 cents ea. at 1000bulbs) is essential even if converting to LED.

I dislike instant start ballasts and prefer rapid or programmed start when obtainable at sane price. You want programmed start for hard to reach locations or frequently cycled lights e.g. Bathroom or on a motion sensor.

Tubes don't "burn out", they get dimmer, scorch their ends and then flicker or barely light. An abrupt failure is tombstone or ballast.

  • "Shopping off limits" but a definite +1 for 1000bulbs - I've bought various things from them over the years - good prices, excellent support. Dec 6, 2018 at 15:37
  • I appreciate most of the info, but I'm not interested in buying more ballasts :D
    – Daniel
    Dec 7, 2018 at 14:42
  • @Daniel just in the other answer you say you are on a budget. I pay about $4 a ballast after shipping (bulk buy), so with tubes it costs me about $8 a fixture for top-shelf stuff. I believe buying quality works, and what I see in the LED market at this price tier does not give me warm fuzzies. Dec 7, 2018 at 18:19
  • I'm on a budget with a mission to rid our business of fluorescents: 1. They require more maintenance - changing tubes more frequently, and changing ballasts requires a moderate amount of time and skill. 2. They provide less light. 3. They provide more depressing light. 4. They use more energy. 5. They're more harmful for the environment in terms of disposal. 6. They're easier to break and more dangerous when broken. The only advantage I see for fluorescents is, of course, the upfront cost being substantially less.
    – Daniel
    Dec 12, 2018 at 20:47
  • 1
    @Daniel 1 and 6 conceded. 2 and 4 My tubes give 4900lm for 62W. 3 actually the win is to Fluorescent, since 90+ CRI tubes are readily available and they don't flicker. LED light is too notchy even if the technical CRI score is good. 5 the mercury has been dramatically reduced. That said, there's certainly nothing wrong with LED, and your rollout is 100% reasonable IMO. I use it some places (archival: avoid UV), but right now I'm enjoying the quality surge and cost crash of Fluorescent's last gasps. Dec 12, 2018 at 21:14

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