Situation: Three 96" ceiling fixtures lined up end to end.
Bulb 1 on single bulb ballast works fine.
Bulbs 2 & 3 on dual bulb ballast - #2 works fine, #3 has shadowy rings moving back and forth.
Replaced #3 with several new bulbs - same symptom.
Pulled dual ballast and replaced with single bulb ballasts in both fixtures #2 and #3. #2 bulb still works fine. But #3 STILL has the moving rings.
What to do?
This is a pure guess, but perhaps the tombstone connectors, due to age, are not making great contact. They are wired so that the bulb pin must be inserted to complete the 120 AC circuit to the ballast.
Might a light coating of no-ox on the pins help? That's easy to do so I may try that.
More closely observing other bulbs in the building, I found that quite a few have varying degrees of the same problem.
Any and all suggestions will be muchly appreciated.
Thanks.

 

Is it cold where the lights are installed?

 

Not really. They are inside where it gets no lower than maybe 70F.

 

It could be that you are not getting a good ground to all the fixtures. Best to run a ground wire and connect it at each fixture rather than relying on the metal to metal contact at the end clips.

One other good idea is when you install a new bulb or ballast, and first turn it on, leave it on for 24 hours. This is called burning in, and will increase the life and quality of the lights.

 

Very good point.
I had considered that, as the whole building wiring appears to use BX conduit for ground. I never have trusted that.
I'll ground each ballast body to where the BX comes into the first fixture.
I never thought about your second suggestion. But that's why you're the expert.
Thanks so much for your help.

 

Also make sure the ballast matches the lamps, Wattage etc.. Always change both lamps or all lamps for the particular ballast.