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Fluorescent Bulb Failure Explanations?

04/08/2016 1:42 AM

Attached are some photos of the current and light output waveforms from some 40W, T12, F40CW type, 4 foot fluorescent bulbs. Could you provide a technical explanation of how these bulbs failed? All bulbs were used in the same fixture using the same magnetic type rapid start ballast.

Bulb 1 is a new properly working bulb.

Bulb 2 fails to light most of the time. When it does light, the waveforms in the Bulb 2 photo are produced. Both heaters light up, even if the bulb does not light up. The bulb failed after about two years.

Bulb 3 lights every time, but the output is dim. One heater is open. As you can see from the waveforms, this bulb only produces light every half cycle. How is this possible? This bulb lasted about twenty years.

The new bulb (Bulb 1) has a significant DC light output component while the failed bulbs go to zero light output during part of the cycle. Is this due to design differences, such as a different phosphor, or is this failure related?

What does the jagged light output waveform on bulb 2 indicate?

Why does bulb 3, which has an open heater, light up every time, while bulb 2 fails to light most of the time with both heaters operating?

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#1

Re: Fluorescent bulb failure explanations?

04/08/2016 1:54 AM

Bulb 1 is a happy bulb. Well adjusted and content.

Bulb 2 is very confused and conflicted. It burned itself out after much internal hopelessness. Not a good life.

Bulb 3 just doesn't know any better and thinks it's the brightest bulb in the room. It will outlive you.

You should do your own homework.

Show us some pictures of nails. We'll pick out the dullest one for you.

Different loads of bricks? We'll show you the load that is short one brick.

Do we get a prize?

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#2

Re: Fluorescent bulb failure explanations?

04/08/2016 4:34 AM
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#3

Re: Fluorescent bulb failure explanations?

04/08/2016 6:39 AM

So how many dollars in labor and hours of time was spent analyzing the three lights opposed to just changing out the bad ballasts and bulbs?

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#4

Re: Fluorescent Bulb Failure Explanations?

04/08/2016 10:17 AM

The ballast is probably dying. Part of it has failed or is in the process of failing. You can replace the ballast, but it's probably cheaper and easier to just replace the entire fixture.

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#9
In reply to #4

Re: Fluorescent Bulb Failure Explanations?

04/11/2016 8:43 AM

Probably replace with a more efficient type as well. T8, T4, LED??

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#5

Re: Fluorescent Bulb Failure Explanations?

04/08/2016 11:45 AM

Twenty years is awesome life. I had a 30 watt 2 foot fluorescent bulb over the kitchen sink that stayed on 24/7 as fill in during the day and night light at night and it would only last about 8 years before it would start to flicker. Now we have a GE 7 watt LED fixture from Sam's Club that puts out more light with a nicer CRI than the fluorescent.

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#6

Re: Fluorescent Bulb Failure Explanations?

04/08/2016 12:31 PM

Bulb 1 looks to be nominal.

Bulb 2 is either loose in the fixture or has a loose coil that is bouncing on the coil clamp rather than being rigidly held in place.

Bulb 3 has a broken coil or connection to one end of the lamp. It is rectifying the current just like a diode. Same thing happens in an old vacuum tube type diode.

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#7
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Re: Fluorescent Bulb Failure Explanations?

04/09/2016 12:13 PM

Bulb #3 is rectifying the current and emitting light. It must be one of the earliest light emitting diodes!

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#10
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Re: Fluorescent Bulb Failure Explanations?

04/11/2016 12:25 PM

I always called it a bi-polar DC device. Under the right conditions, the DC will drive the mercury to one end of the lamp after some time.

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#8

Re: Fluorescent Bulb Failure Explanations?

04/09/2016 10:31 PM

Bulb 2 probably has a bad ballast, putting too much current in the bulb or the heaters.

Bulb 3 lights every half cycle because one heater is open.

The jagged waveform indicates that the current is fluctuating rapidly. Old bulbs sometimes emit RF frequencies that cause radio interference. This one may be a candidate.

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#11
In reply to #8

Re: Fluorescent Bulb Failure Explanations?

04/11/2016 1:47 PM

Thanks for the replies. Please note the following:

All the bulbs were fired up using the same ballast. This ballast is in good working order.

The jagged waveform on bulb 2 is the light output waveform (bottom waveform). The current waveform (top waveform) is not jagged, and looks the same as the new bulb 1.

I have had many bulbs fail with an open heater. This is the only one that would light up after such a failure.

I am still wondering about the DC offset in the light output waveform of new bulb 1. The failed bulbs go to zero light output during part of the cycle. Is this due to design differences, such as a different phosphor, or is this failure related?

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#12
In reply to #11

Re: Fluorescent Bulb Failure Explanations?

04/13/2016 5:50 AM

Bulb #2 is at its end of life (the internal "atmosphere" has changed to the point its UV emitting is unstable).

Bulb #3 has its open heater/filament broken very close to one of its ends. Try to rotate the bulb by 180 degrees - the internal current might now flow through its (broken) filament (heating it) and the bulb might light normally.

Regarding the DC offset, it's most probably related to the lighting inertia (afterglow) of the phosphor.

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#13
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Re: Fluorescent Bulb Failure Explanations?

04/14/2016 1:22 PM

As Alex mentioned, bulb 2 has something going on with the emitter on the heater coils. It could be contamination but the life is nearly gone from that bulb. Sometimes the coils are poorly clamped by the support wire, but then your current waveform would be quite different.

As to DC offset in bulb 1, there isn't any. As the current crosses through zero, the light falls off rapidly. The persistence of the phosphor is dependent on the manufacturer. It is obvious that you are using a magnetic ballast or else you simply wouldn't see the fall in light output as the current crosses through zero.

Remember there is no power, thus no light, when the current is zero, twice per cycle.

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#14
In reply to #13

Re: Fluorescent Bulb Failure Explanations?

11/17/2016 1:07 PM

Higher resolution photos of bulb waveforms.

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#15
In reply to #14

Re: Fluorescent Bulb Failure Explanations?

12/15/2016 1:09 PM

OK, with the limited information seen on the screens this is all that can be determined:

Bulb 1 has a phosphor with a slightly longer persistence, thus the “DC” component. It doesn’t go dark during the crossover of the applied voltage.

Bulb 2 has a seriously unstable arc, thus the non-uniform light output. During the AC power cycle, one lamp coil acts like an Anode while the other acts like a Cathode. When the AC cycle changes polarity, the Anode/Cathode function is reversed. The coil heat is supposed to increase the energy level of the emitter coating whose purpose is to provide energetic electrons in the area of the coil when it is its turn to become an Anode. The secondary oscillation seen in the light output could be a problem with contaminated emitter coating or a very slow air leak that eventually kills the lamp. Typically an air leaker will not make it out to 2 years. It is more likely to die within a couple of weeks. That leaves the emitter coating. If the bulb is yellowed near the coils then it was not completely processed during the manufacturing process. On the other hand, if the coated coils were stored in air too long before being used, they may have trapped other gasses in the emitter mix. Lastly, it is possible that the fluorescent powder coating is contaminated, then the current looks just fine, but the light output is unstable. The lamp voltage would change if the lamp impedance was changing. The current is nice and stable indicating that the plasma is stable. There are 7 natural isotopes of mercury in nature. I don’t suppose this is a special lamp?

Lamp 3 is doing what is commonly called rectifying. One end acts nicely as an Anode while the other is acting nicely as a Cathode. When the AC polarity switches, the arc is extinguished except for a little bit of conductivity near the peak. Old tube circuits used to use this principal before solid state diodes became available.

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