Fluorescent tube questions 1

[Mac56]

I've been told if a fluorescent tube is black on one end, the fixture has a ballast problem. If the fluorescent tube is black on both ends, then the tube was the problem or in other words, the tube is defective.

Also, the blackening of the ends is what burns out ballasts?

Any feedback on this?

Thanks....Mac

 

[dpc]

That's a new one on me. Sounds like fairly normal aging of the lamp. Most failure modes in ballasts that I've seen result in the lamp not firing at all, or the ballast bursting into flames.

I'd always replace the lamps first. If the lamps are failing rapidly, you might suspect the ballast.

Maybe someone else has a more definitive answer.

 

[Lewish]

Blackening is normally associated with aging. It is the mercury bonding to the glass. May happen on one end or both. Depends of the construction of the tube.
If tubes are failing too frequently, suspect the ballast, but usually it will burn out first.

 

[Foxfur]

In older mag ballasts, the dripping black glop collecting on the ballast cover is a darn good sign the ballast has had it.
On the newer electronic ballasts, that all too familiar smell of fried electronics is the give away.

I've never heard of that rule of thumb before. I've had ballasts be just fine when running a tube with black ends. I've put black ended tubes in fixtures with new ballasts and had them work like new (almost). There does not seem to be any hard and fast rules in this arena. But that's just my take from my experience.

Foxfur

 

[dnvm1]

The blackened ends on a fluorescent lamp is the sign of use and age. When a lamp is off the ballast needs to pump a high starting voltage into the lamp to ignite the gasses. Once the lamp is started and is lighted the ballast automatically switches to a normal operating voltage. Most of the new ballasts if the lamp does not start after so many tries it will shut down. Foxfur stated that the older ballast leaked black goo when they went bad. That goo is a tar that is used for heat tranfer from the inner components to the case. When an older ballast trys to start a bad lamp it will continue until it burns itself up causing the goo. So all this actually means is that it is very important to use the specified lamps with the proper ballast to reduce any chance of having your own flaming ballast.

 

[Mac56]

Thanks guys for all the feed-back. Does anyone know if the presumptions:

A). black on 1 end indicates a ballast problem
or
B). black on both ends indicates a tube problem

hold any water?

Thanks again.....Mac

 

[busbar]

From

http://www.ecmweb.com/ar/electric_troubleshooting_discharge_lamp/

“Heavy premature end darkening (usually at only one end) is a good indication that one cathode is not properly heated and, therefore, the heater circuit is incomplete. This isn't the same as gray or brownish bands that occur about 2 in. from the lamp base (with the edge of each band on the side nearer to the base being sharper). This latter symptom occurs when the lamp's cathode coating wears out. While such bands may detract from the appearance of the lamp, moderately dark bands have no significance in regard to the life or performance of the lamp.”

If the problem involves lamps in a tanning bed, see

http://www.cosmedico.com/north_am/product/pdf/end_darkening.pdf

;-) ;-)

 

[Mac56]

Thanks BB. I could't get either of those pages to open up, tho.

Mac

 

[busbar]

Vaguely related—fluorescent “lamp seasoning”…

http://www.nema.org/DocUploads/B109F465-230C-4B7B-A73C3AFE437BC8AB//LSD23.doc

 

[don01]

hi all
I've put a star on busbar for finding the first difinitive statement for what I had always thought was a rule of thumb.

My twobits worth ( or 2 bob's worth here):
99.9% of tubes I've seen go black when the tungsten coats the glass casing as it leaves the (heater) elements. Remeber radio tubes where always grey silver after a while(no I haven't seen it on TX tubes so I'm not sure about them).
This coating is a sure sign the tubes are OLD by this time the light output is very low and you probably have extra lights running to compensate.
This will be refected in your power bill and I believe it's more cost effective to replace them every year or about 4~5,000 hrs. By routinely changing the tubes we can plan our work and aren't jumping all over the place.
My local rep. assures me triphos types are good for 2 years and 80% output so we are trialing that now but I won't know for 18 months.
regards
Don