Small incandescent lamp failure curiosities

[Travis Evans]

Since some people are concerned about the activity level on this
newsgroup, I'll post something.

Something that happened last night made me curious. My flashlight
suddenly would not turn on when it was working fine just a little while
ago. If the batteries were low, the lamp would have dimmed, but not
suddenly stop working altogether. After reading a message here some
time back about the life of flashlight lamps being very short, I
figured the lamp had burned out since I use that flashlight nearly
every day, often for an hour or more at a time. I was actually
wondering how it had lasted for so many months with that much usage
(likely because I use AA NiMH rechargeable batteries instead of
alkaline due to short battery life--the voltage of rechargeable
batteries is slightly lower).

The lamp evidently did fail--there is no continuity on the lamp contacts
(there is with a known good lamp), and putting in a good lamp made the
flashlight work again, and the bad lamp still does not work in a
different flashlight. (In case it's important, the markings on the
lamps read "PHILLIPS KPR102 2.4V 0.7A H K 1K3".) So that makes me
curious--if the filament appears intact, what is it that breaks the
circuit?

I've seen this happen in mini-Christmas lamps as well--they stop
working, but the filament doesn't look broken. I figured that with
Christmas lights, the shunts that are designed to short out the lamps
when the filaments open may sometimes short before filament failure,
but a flashlight lamp doesn't have a shunt.

An unrelated but interesting thing that happened last Christmas--a lamp
on a set of lights we had hung inside the house was accidentally
broken. The rest of the string continued operating, and it was a while
before I finally replaced it (probably would have been safer to have
replaced the broken lamp immediately, I admit). But on the broken
lamp, the filament was completely intact! Wouldn't air exposure to an
operating filament burn it up immediately? So I guess maybe the shunt
somehow shorted before or during breakage, extinguishing the filament
before that could happen.

 

[Don Klipstein]

Since some people are concerned about the activity level on this
newsgroup, I'll post something.

Something that happened last night made me curious. My flashlight
suddenly would not turn on when it was working fine just a little while
ago. If the batteries were low, the lamp would have dimmed, but not
suddenly stop working altogether. After reading a message here some
time back about the life of flashlight lamps being very short, I
figured the lamp had burned out since I use that flashlight nearly
every day, often for an hour or more at a time. I was actually
wondering how it had lasted for so many months with that much usage
(likely because I use AA NiMH rechargeable batteries instead of
alkaline due to short battery life--the voltage of rechargeable
batteries is slightly lower).

The voltage of rechargeable batteries throughout discharge is more
constant than that of disposable batteries. More-used disposable
batteries are less able to burn out a flashlight lamp ("bulb") than
rechargeable batteries are.

Do keep in mind that most flashlight lamps have design ratings around
1.2-1.25 volts per cell - "supposed average condition" (with load applied)
with disposable cells, and not much off the mark for NiCd and NiMH
rechargeable ones doing most of their discharge duty into a significant
load!

The lamp evidently did fail--there is no continuity on the lamp contacts
(there is with a known good lamp), and putting in a good lamp made the
flashlight work again, and the bad lamp still does not work in a
different flashlight. (In case it's important, the markings on the
lamps read "PHILLIPS KPR102 2.4V 0.7A H K 1K3".) So that makes me
curious--if the filament appears intact, what is it that breaks the
circuit?

Did you examine the filament with enough magnification to see a break of
only several to a few dozen micrometers or in the ballpark of a couple
thousandths of an inch?

I've seen this happen in mini-Christmas lamps as well--they stop
working, but the filament doesn't look broken. I figured that with
Christmas lights, the shunts that are designed to short out the lamps
when the filaments open may sometimes short before filament failure,
but a flashlight lamp doesn't have a shunt.

An unrelated but interesting thing that happened last Christmas--a lamp
on a set of lights we had hung inside the house was accidentally
broken. The rest of the string continued operating, and it was a while
before I finally replaced it (probably would have been safer to have
replaced the broken lamp immediately, I admit). But on the broken
lamp, the filament was completely intact! Wouldn't air exposure to an
operating filament burn it up immediately?

It usually takes anywhere from a few seconds to several minutes. Air
exposure to a tungsten filament lamp designed to work with a vacuum (which
is most designed to work with power near or under 1 watt or current
under .2 amp) will lower the filament temperature, possibly allowing the
filament to operate for minutes rather than seconds.

So I guess maybe the shunt somehow shorted before or during breakage,

extinguishing the filament before that could happen.

But did the lamp in question glow? The filament could have broken in a
more microscopic way!

Travis Evans

- Don Klipstein ([email protected])

 

[SimonLW]

Since some people are concerned about the activity level on this
newsgroup, I'll post something.

Something that happened last night made me curious. My flashlight
suddenly would not turn on when it was working fine just a little while
ago. If the batteries were low, the lamp would have dimmed, but not
suddenly stop working altogether. After reading a message here some
time back about the life of flashlight lamps being very short, I
figured the lamp had burned out since I use that flashlight nearly
every day, often for an hour or more at a time. I was actually
wondering how it had lasted for so many months with that much usage
(likely because I use AA NiMH rechargeable batteries instead of
alkaline due to short battery life--the voltage of rechargeable
batteries is slightly lower).

The lamp evidently did fail--there is no continuity on the lamp contacts
(there is with a known good lamp), and putting in a good lamp made the
flashlight work again, and the bad lamp still does not work in a
different flashlight. (In case it's important, the markings on the
lamps read "PHILLIPS KPR102 2.4V 0.7A H K 1K3".) So that makes me
curious--if the filament appears intact, what is it that breaks the
circuit?

I've seen this happen in mini-Christmas lamps as well--they stop
working, but the filament doesn't look broken. I figured that with
Christmas lights, the shunts that are designed to short out the lamps
when the filaments open may sometimes short before filament failure,
but a flashlight lamp doesn't have a shunt.

An unrelated but interesting thing that happened last Christmas--a lamp
on a set of lights we had hung inside the house was accidentally
broken. The rest of the string continued operating, and it was a while
before I finally replaced it (probably would have been safer to have
replaced the broken lamp immediately, I admit). But on the broken
lamp, the filament was completely intact! Wouldn't air exposure to an
operating filament burn it up immediately? So I guess maybe the shunt
somehow shorted before or during breakage, extinguishing the filament
before that could happen.

--
Travis Evans
[The email address on this post is valid, but may change from time to
time. Make sure you use the latest email address; if you use an old
one, I will not receive your message.]

In my experience, the filament always breaks at the top of the arch and the
break is very small. It may look like the filament is fine, but a strong
magnifying glass reveals a break.

One side note: After trying a good quality LED flashlight with good
reflector design and a Luxeon emitter, I'll never go back to incandescent
flashlights again.
-S

 

[Victor Roberts]

Since some people are concerned about the activity level on this
newsgroup, I'll post something.

Something that happened last night made me curious. My flashlight
suddenly would not turn on when it was working fine just a little while
ago. If the batteries were low, the lamp would have dimmed, but not
suddenly stop working altogether. After reading a message here some
time back about the life of flashlight lamps being very short, I
figured the lamp had burned out since I use that flashlight nearly
every day, often for an hour or more at a time. I was actually
wondering how it had lasted for so many months with that much usage
(likely because I use AA NiMH rechargeable batteries instead of
alkaline due to short battery life--the voltage of rechargeable
batteries is slightly lower).

The lamp evidently did fail--there is no continuity on the lamp contacts
(there is with a known good lamp), and putting in a good lamp made the
flashlight work again, and the bad lamp still does not work in a
different flashlight. (In case it's important, the markings on the
lamps read "PHILLIPS KPR102 2.4V 0.7A H K 1K3".) So that makes me
curious--if the filament appears intact, what is it that breaks the
circuit?

[snip]

As others have stated, the filament probably has a small
break in it. Unlike the longer filaments in higher voltage
lamps, the filament in your low voltage lamp is so short
that it can remain in the same position even if broken.

--
Vic Roberts
http://www.RobertsResearchInc.com
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[Travis Evans]

Did you examine the filament with enough magnification to see a
break of
only several to a few dozen micrometers or in the ballpark of a couple
thousandths of an inch?

I don't have a means of viewing it with that much magnification. I
tried looking at it a few hours ago with a magnifying lens (the fact
that my extreme nearsightedness allows me to focus on objects 4-10 cm
from my eyes with my glasses removed probably gave me some additional
magnification assistance), and I saw what appears to be a break in the
filament at the very top part of the arch (though it's hard to tell),
but only if I hold it at particular angle. At all other angles, it
looks continuous.

It usually takes anywhere from a few seconds to several minutes.
Air
exposure to a tungsten filament lamp designed to work with a vacuum
(which is most designed to work with power near or under 1 watt or
current under .2 amp) will lower the filament temperature, possibly
allowing the filament to operate for minutes rather than seconds.

extinguishing the filament before that could happen.

But did the lamp in question glow? The filament could have broken
in a
more microscopic way!

I wasn't around when the lamp was broken, so I don't know what happened
then. I know that when I saw it later, it did not glow when the string
was plugged in.

After I removed the broken lamp, I studied it for a while. Then the
filament started coming off the support wires, so I took it off, and it
appeared to stay in one piece as I handled it. I then played with it,
seeing how far I could stretch it with my fingers before it broke in
half. I don't remember how far; I think it became about two or three
times longer after stretching out the coil before it broke (it was a
bit difficult to get a firm grasp on the ends due to its thinness).

 

[Travis Evans]

One side note: After trying a good quality LED flashlight with good
reflector design and a Luxeon emitter, I'll never go back to
incandescent flashlights again.

I haven't yet found a place that sells good LED flashlights. I bought a
ten or so dollar "Brinkman" 2 AA white LED flashlight, but I wasn't all
that happy with it because the beam is far too narrow to be very useful
and can't be adjusted. I guess that's what I get for buying something
from Wal-Mart. ;-)

The LED flashlight has better battery life, though. My conventional 2
AA flashlight only runs an hour or two of continuous use on my NiMH
batteries before needing to be recharged; I estimate the LED one lasts
about 4-6 times longer. I prefer using rechargeable batteries because
I drain them often enough that disposable batteries would be
uneconomical (and generate a lot of waste).

 

[JohnR66]

One side note: After trying a good quality LED flashlight with good
reflector design and a Luxeon emitter, I'll never go back to
incandescent flashlights again.

I haven't yet found a place that sells good LED flashlights. I bought a
ten or so dollar "Brinkman" 2 AA white LED flashlight, but I wasn't all
that happy with it because the beam is far too narrow to be very useful
and can't be adjusted. I guess that's what I get for buying something
from Wal-Mart. ;-)

The LED flashlight has better battery life, though. My conventional 2
AA flashlight only runs an hour or two of continuous use on my NiMH
batteries before needing to be recharged; I estimate the LED one lasts
about 4-6 times longer. I prefer using rechargeable batteries because
I drain them often enough that disposable batteries would be
uneconomical (and generate a lot of waste).

--
Travis Evans
[The email address on this post is valid, but may change from time to
time. Make sure you use the latest email address; if you use an old
one, I will not receive your message.]

Most LED flashlights have a fixed beam. The best I found is actually a low
price for a Luxeon LED light ($15). It is the Task Force brand that takes
3AA batteries I found at Lowes. It is plastic, but performs well. Like most
smaller Luxeon flashlights, the beam is somewhat diffuse, getting dimmer
more off axis. Over all, a very nice light to work by. Comparing with my 2
D-cell krypton flashlight, this light blows it into the weeds as far as
brightness goes. I have yet to run the batteries down. I expect about 6
hours of light from it.

John

 

[Jeff Waymouth]

Low voltage filaments use wire with heavier diameters.

Jeff Waymouth

 

[Jeff Waymouth]

No, higher voltage filaments use thinner diameter wire. A 277V filament
has a much smaller diameter wire than a 12V filament

Jeff Waymouth

 

[Jeff Waymouth]

Nope, missed it entirely --sigh--. That's what I get for checking the
newsgroup first thing in the morning, before the coffee begins to take
effect. Sorry.

Jeff Waymouth