Why Do Some Fluorescent Lights Flicker While Others Don't?

[Buzz Bloom]

A Mystery re Fluorescent Lights

I have a fixture F1 from the 1960s with two 2' fluorescent lights B1 and B2. Recently they both began to flicker. A second fixture F2 has a single 2' light B3 which did not flicker.

In F2 I replaced B3 with B1. It did not flicker. I then replaced in F2 B1 with B2. It did flicker. I then in F1, put in B1 and B3. There was no flicker.

The Mystery: Apparently in F1 the bad bulb B2 not only flickered itself, it also caused the good F1 to flicker.
Has anyone an solution explaining this mystery?

 

[Nidum]

Possibly caused by a life expired starter . Try putting a new one in .

 

[NascentOxygen]

The tube prone to flickering is getting on in years, is it? Near the ends of the glass is getting dark?

Could you notice whether the flickering pair were flickering in phase—or exactly in antiphase?

 

[Averagesupernova]

A Mystery re Fluorescent Lights

I have a fixture F1 from the 1960s with two 2' fluorescent lights B1 and B2. Recently they both began to flicker. A second fixture F2 has a single 2' light B3 which did not flicker.

In F2 I replaced B3 with B1. It did not flicker. I then replaced in F2 B1 with B2. It did flicker. I then in F1, put in B1 and B3. There was no flicker.

The Mystery: Apparently in F1 the bad bulb B2 not only flickered itself, it also caused the good F1 to flicker.
Has anyone an solution explaining this mystery?

Yes, this is common.

 

[Buzz Bloom]

Hi NO:
Thanks for your questions.

The tube prone to flickering is getting on in years, is it?

Yes.

Near the ends of the glass is getting dark?

Yes.

Could you notice whether the flickering pair were flickering in phase—or exactly in antiphase?

The flickering was too fast to distinguish the relative phase.

Regards,
Buzz

 

[NascentOxygen]

The flickering is half your line frequency?

I think the origin lies in the deteriorating emission of one of the aging filaments. When it goes positive it needs to overcome a higher voltage to achieve conduction so ends up conducting less strongly or for less of its half-cycle making the light output lower on that polarity half-cycle. The darkening areas on the glass—that's metal that has evaporated off the electrodes.

You could probably fashion a simple stroboscope to determine whether the companion tube dims or brightens when the first dims.