We have 2 circular florescent ceiling light fixtures on a single switch. Last night neither bulb would come on. But this morning they are working fine.

I had checked the circuit breaker, that was OK (other lights attached to that circuit breaker were working).

We have noticed that we are not getting very long out of the bulbs recently, having to change them withing 12 months of replacement.

Each fixture has one bulb.

Note I am in Ireland: 230vac & 50hz

Also, I don't know if this has anything to do with it, but it seems that 'quality' of electricity in our area is poor. Occasionally a circuit-breaker in the house will trip, and exactly simultaneously one of the neighbors' intruder alarms will fire (as they do when power is interrupted) or the power in the neigbourhood will vanish for a second, resetting clocks and computers.

  • Are both of these fluorescent tubes in the same fixture? The ballasts in these fixtures wear out. You can check the ac voltage in your house and see if it changes over the course of the day. Apr 5, 2017 at 13:09
  • Two separate fixtures, question updated.
    – Ken
    Apr 5, 2017 at 13:10
  • Find a receptacle on the same circuit as these fixtures. Use an a/c voltmeter and read the voltage at different times in the day. The absolute accuracy is not so important as whether this would reveal that the voltage is lower at some times than others. Also the voltage could be lower throughout your house if high power appliances are dragging down the voltage. These would be electric water heater, electric ac/heat, electric range, electric clothes dryer. Apr 5, 2017 at 13:15
  • If both fixtures are the same model and age, they might have the same marginally functioning ballasts. When the voltage in that circuit is above a certain value the lights work and when the voltage is below it they don't. I think the "quality" of power is a problem in a lot of places. In Dallas we have had problems with momentary outages. Apr 5, 2017 at 13:36
  • Ken, where are you? This would be helpful in your getting useful advice. If you are in the UK I would not be able to give specific detailed advice, but if you make that known, it might stimulate someone there to participate.My thought is that if you are having trouble with these fluorescent fixtures, change to LED fixtures. What specific ones are available for UK power I couldn't say. Apr 5, 2017 at 14:22

1 Answer 1


Change the ballast

Especially if it hums or buzzes. Old magnetic ballasts (heavy, transformer in them) are notorious for failing in a way which burns up bulbs prematurely. They also flicker and are cranky in the cold. A worn tube will be finicky about starting; what's happening is the voltage required to strike the tube increases as the tube ages, until the ballast can no longer strike the tube.

Also consider North American suppliers for the ballast, most ballasts these days are multi-voltage 100-240V and 50/60Hz, just make sure of that.

I don't know if the T8 type bulbs exist in your country, but now is a good time to think about switching from T12 to them. T8 has the same socket as T12 so you do not need to alter the fixture (outside of changing the ballast, which you are probably doing anyway). The ballast must match the bulb type, so select a T8 ballast. The T12s are obsolete.

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