OT?: Lightbulb life, curiousity

[w_tom]

If speculating, then at least put some numbers to that
'massive stress'. Filament must be severely damaged for that
gentle 'power-on' stress to break it. Often that stress is so
minimal that the filament instead fails by vaporizing the
little that remains at the hot spot. A far more severe stress
is people walking on the floor above.

Filament gets real hot; therefore it must be high stress?
Without numbers to define stress, then stress is only wild
speculation. The point of my initial post that resulted in so
much emotion: They did not know. They speculated. They did
not first consult industry sources, numbers, or citations.
They just speculated. Speculation creates junk science
reasoning.

Once the filament is so badly damaged, then dark spots
appear inside the glass envelope. Then either the bulb fails
on power on OR fails during operation some hours later. My
last bulb failed some hour after power on. Most never notice
failure during operation but always notice the failure on
power on. Just another reason why observation is not a valid
fact. But again, damage that causes failure is defined by ...
hours of operation.

Numbers, equations, citations, etc were provided
previously. If you think power on causes so much stress,
well, where are both numbers and citations? Wild speculation
and no numbers are symptoms of junk science. Please don't
make that mistake. Enough junk science reasoning (followed by
emotional outbursts when bluntly confronted) has already been
posted in this discussion.

You are assuming the seven times or tens times current on
power up is destructive. This assumption is answered in
another post.

 

[w_tom]

Filament temperature determines vaporization. When current
is high, filament is cool.

What is the maximum current in a typical 20 amp wire. Maybe
300 amps? Many will then assume 300 amps will always be
destructive. Wrong. That same wire can conduct thousands of
amps if only for a short period - without any damage. Same is
true of that seven or ten times current during startup
illumination. Large current is quite short. Filament is cool
during that short period. Therefore no significant filament
vaporization during that high current period.

 

[Dan Bloomquist]

Filament temperature determines vaporization. When current
is high, filament is cool.

What is the maximum current in a typical 20 amp wire. Maybe
300 amps? Many will then assume 300 amps will always be
destructive. Wrong. That same wire can conduct thousands of
amps if only for a short period - without any damage. Same is
true of that seven or ten times current during startup
illumination. Large current is quite short. Filament is cool
during that short period. Therefore no significant filament
vaporization during that high current period.

But not at a weak spot. There the resistance is higher. There you have
light bursting from the wire before the rest of the filament comes up to
temperature.

Best, Dan.

 

[John Fields]

If speculating, then at least put some numbers to that
'massive stress'. Filament must be severely damaged for that
gentle 'power-on' stress to break it. Often that stress is so
minimal that the filament instead fails by vaporizing the
little that remains at the hot spot. A far more severe stress
is people walking on the floor above.

---
PKB. Where are the numbers? How many amps/second on turnon? at what
conduction angle? What does the resistance of the hot spot have to be
for that vaporization on turn-on to occur? What diameter does that
resistance correspond to? At what tensile (or shear) strength will
the filament part? How severe is the stress caused by the foosteps
overhead? How hard do the footsteps have to hit the floor for the
filament to part?
---

Filament gets real hot; therefore it must be high stress?
Without numbers to define stress, then stress is only wild
speculation. The point of my initial post that resulted in so
much emotion: They did not know. They speculated. They did
not first consult industry sources, numbers, or citations.
They just speculated. Speculation creates junk science
reasoning.

---
So post some numbers to support _your_ claims, above.
---

Once the filament is so badly damaged, then dark spots
appear inside the glass envelope. Then either the bulb fails
on power on OR fails during operation some hours later. My
last bulb failed some hour after power on. Most never notice
failure during operation but always notice the failure on
power on. Just another reason why observation is not a valid
fact. But again, damage that causes failure is defined by ...
hours of operation.

---
That's foolish reasoning in that if a lamp blows when you turn it on
you're immediately mad aware that the lamp has failed. In the other
case you won't know immediately unless you're in the room when it
happens, but if you came back later and the lamp has blown you'll
notice it and, since you'll know that it didn't let go when you turned
it on it must have failed when it was operating. Duh.
---

Numbers, equations, citations, etc were provided
previously. If you think power on causes so much stress,
well, where are both numbers and citations?

 

[John Fields]

Filament temperature determines vaporization. When current
is high, filament is cool.

What is the maximum current in a typical 20 amp wire. Maybe
300 amps? Many will then assume 300 amps will always be
destructive. Wrong. That same wire can conduct thousands of
amps if only for a short period - without any damage. Same is
true of that seven or ten times current during startup
illumination. Large current is quite short. Filament is cool
during that short period. Therefore no significant filament
vaporization during that high current period.

---
How about some numbers?

Length / Resistance of the wire? Temperature rise as a function of
current? Thousands of amps for how long? How short is a short
period? Mechanical forces on the filament during a cold start? Time
constant of the filament?

 

[w_tom]

By weak spot, I assume you meant the hot spot. The hot spot
is created by vaporization. Once the hot spot has formed,
then a bulb is doomed. As noted earlier, bulb fails either in
normal operation or in power on. The gentle force of power-on
can cause a bulb in its last 10 hours of operation to fail
during the power on. Indication that the bulb will soon fail
- that excessive filament damage has already occured - is
blackened deposits inside the glass envelope. IOW failure
even during power on is due to damage created by hours of
operation.

Many, such as some early posters, saw a bulb fail during
power on and then assumed power on was destructive. Industry
research (complete with pictures that showed the hot spot as
darker) explain why a bulb fails either while powered or
during power on. Failure is created by hours of operation;
damage due to filament vaporization.

Light bulb failure demonstrates what is required to create a
fact. A fact is explained theoretically AND is observed
experimentally. Both conditions are required. Those who saw a
bulb flash during power on only had experimental
observations. Therefore they speculated. When underlying
principles (filament vaporization) is included, then
sufficient information exists to build a fact. My initial
post criticized others who somehow knew only because they had
observed a bulb fail on power on. They were performing
classic junk science reasoning. They were violating basic
science principles as even taught in junior high school. They
did not first learn the principles and numbers of light bulb
operation.

Why would that seven or ten times current cause a bulb
failure? The filament has been so thinned in one spot by
hours of operation that a doomed incandescent bulb burns out -
either during power on or some hours later.