Dying fluorescent lamp flashes

B

Bob Masta

Guest
Hello, all.
I have an old compact fluorescent lamp that has
served admirably for many years. I finally had to
take it out of service because it started flashing.
The lamp is the old non-electronic ballast type. The
ballast appears to be nothing more than a big inductor
in series with the tube. The lamp lights OK at first,
then after several seconds (maybe as much as 30)
it starts flashing: The tube goes dark, then the
heaters on the ends glow, there is a blue flash
visible from the end where there is no phosphor,
the lamp lights... and a second or two later the
whole thing repeats.

So, any idea what causes this? When the tube is
lit, it appears to be about normal, or maybe with
a bit of extra flicker. My best guess is that
"something" has changed in the gas, either leaked
out or plated out on a surface, etc, such that it
will only conduct properly when warm. So it starts
OK, but after the heaters cool down it can no longer
support the discharge. But what exactly is that
"something" that has changed?

Thanks!



So
Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
 
In article <41d6bec9.3349123@news.itd.umich.edu>, Bob Masta wrote:
Hello, all.
I have an old compact fluorescent lamp that has
served admirably for many years. I finally had to
take it out of service because it started flashing.
The lamp is the old non-electronic ballast type. The
ballast appears to be nothing more than a big inductor
in series with the tube. The lamp lights OK at first,
then after several seconds (maybe as much as 30)
it starts flashing: The tube goes dark, then the
heaters on the ends glow, there is a blue flash
visible from the end where there is no phosphor,
the lamp lights... and a second or two later the
whole thing repeats.

So, any idea what causes this? When the tube is
lit, it appears to be about normal, or maybe with
a bit of extra flicker. My best guess is that
"something" has changed in the gas, either leaked
out or plated out on a surface, etc, such that it
will only conduct properly when warm. So it starts
OK, but after the heaters cool down it can no longer
support the discharge. But what exactly is that
"something" that has changed?
Click to expand...
The heaters (filaments, electrodes) do not support an arc as well as
they used to.

The filaments are coated with a thermionically emissive material. Usage
causes wear and starting also causes wear on this material. It chemically
degrades, evapotates, and/or sputters (molecules of the material get
dislodged by positive ions crashing against the negative electrode).

You reach a point when there is so little left that you need extra heat
to get it to sustain the arc.

Often in fluorescent lamps, the arc does some working from the filament
material itself in addition to or instead of the thermionic coating before
the lamp completely dies. When that happens, some filament material
usually sputters and noticeably blackens the end of the tubing where that
happened.

- Don Klipstein (don@misty.com)
 
Bob Masta submitted this idea :
Hello, all.
I have an old compact fluorescent lamp that has
served admirably for many years. I finally had to
take it out of service because it started flashing.
The lamp is the old non-electronic ballast type. The
ballast appears to be nothing more than a big inductor
in series with the tube. The lamp lights OK at first,
then after several seconds (maybe as much as 30)
it starts flashing: The tube goes dark, then the
heaters on the ends glow, there is a blue flash
visible from the end where there is no phosphor,
the lamp lights... and a second or two later the
whole thing repeats.

So, any idea what causes this? When the tube is
lit, it appears to be about normal, or maybe with
a bit of extra flicker. My best guess is that
"something" has changed in the gas, either leaked
out or plated out on a surface, etc, such that it
will only conduct properly when warm. So it starts
OK, but after the heaters cool down it can no longer
support the discharge. But what exactly is that
"something" that has changed?

Thanks!



So
Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Click to expand...
try replacing the starter. thats a small metal can with 2 terminals on
it.. it removes with a slight twist and pull action. They're cheap.
look at the ends of the tupe. Are they dull or going black? bad tube.

--
This is an automatic signature of MesNews.
Site : http://www.mesnews.net
 
In article <mn.ccac7d5675fcd728.33372@earthlink.net>, Lawrence Oravetz wrote:
Bob Masta submitted this idea :
Hello, all.
I have an old compact fluorescent lamp that has
served admirably for many years. I finally had to
take it out of service because it started flashing.
The lamp is the old non-electronic ballast type. The
ballast appears to be nothing more than a big inductor
in series with the tube. The lamp lights OK at first,
then after several seconds (maybe as much as 30)
it starts flashing: The tube goes dark, then the
heaters on the ends glow, there is a blue flash
visible from the end where there is no phosphor,
the lamp lights... and a second or two later the
whole thing repeats.

So, any idea what causes this? When the tube is
lit, it appears to be about normal, or maybe with
a bit of extra flicker. My best guess is that
"something" has changed in the gas, either leaked
out or plated out on a surface, etc, such that it
will only conduct properly when warm. So it starts
OK, but after the heaters cool down it can no longer
support the discharge. But what exactly is that
"something" that has changed?
Click to expand...
Electron-emitting material on the heaters has worn out from use
and/or from cold starts. This is a normal inevitable failure mode
of hot-cathode fluorescent lamps in general, as well as at least most high
pressure mercury vapor lamps and sodium vapor lamps of either high or low
pressure.

The heaters are normally kept hot enough to thermionically emit
electrons at an adequate rate by heating from the ends of the arc in the
tube. This fails when the thermionically emissive coating is worn away.

- Don Klipstein (don@misty.com)
 
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