Palindrome said:
Hi,
An interesting thing happened in the drawing room tonight.. a standard
40W incandescent lamp failed as I switched the room lights on.
What I saw was a bright flash and a red/white hot something leave the
wall lamp and travel some 8 foot to the floor.
The circuit fuse blew.
The lamp has a darning-needle sized round hole (large pin hole) in the
glass, with a rounded/melted edge. The inside of the glass has a patch
of dark discolouration opposite the hole.
Anyone ever heard of anything like that happening?
It must have produced an incredibly hot and high speed fragment to have
been able to melt through the glass quickly enough to still have the
speed to travel that distance across the room.
What I suspect happened, before I get much into this thread:
The lamp (lightbulb, that is) had a reasonably normal cold-start burnout
with a "burnout arc" forming across the developing break in the filament
and "blowing up" to quickly move and grow to have its terminations being
the ends of the filament. With hardly any filament material in series
with the arc, there is not much to limit its current.
One thing about most arcs: As you feed them more current, they become
more conductive, often even disproportionately. Sometimes as a good
explanation and sometimes to maybe usually as an oversimplified one,
higher current makes an arc hotter, and higher current increases the
percentage of the atoms in the arc being ionized.
So when a "burnout arc" forms in an incandescent lamp and "blows up", it
is limited by any of the following:
1) A fusible link in one of the wires in the lamp (lightbulb) serves as a
fuse and blows.
2) The branch circuit's fuse/breaker blows/trips.
3) The arc dies during the next zero crossing of the line voltage,
preferably before it gets *Really Bad* if 1 or 2 does not occur first.
I have heard of complaints of some incandescent lamps lacking fusible
links in their internal wires. The usual complaint of those is that
burnout arcs draw current surges that blow fuses/pop breakers, ruin
dimmers, or cause the wiring in the lamps (lightbulbs) to vaporize
internal glue (or whatever gets vaporized) and bulbs get popped from their
bases by the pressure of this vapor.
Thankfully, such problems are rare! I would hope that manufacturers
that "cheap out" by not including those fusible links lose sales as a
result!
Now for what else could happen:
I did once overvoltage a 500 watt photographic lamp (ECT), as in
giving about or slightly over 140 volts to a 110-120V 3200K 500 watt unit.
The filament broke from melting, and without a big bright flash, and
apparently one end of one half of the freshly broken hot filament touched
and melted through the glass bulb material.
The glass bulb got a small hole melted into it. The filament did not
get stuck to the bulb, although I do have memory traces of other incidents
where filament fragments stuck to the inner surface of a bulb.
One more datum: In the above incident with an ECT photoflood lamp, the
lamp was powered up without overvoltage and the voltage was increased
gradually over several seconds.
Back to your 40W incandescent:
I suspect that, if your symptoms did indeed occur as you described, you
had some extremely rare bad burnout where a piece of hot filament (or
molten portion thereof) both broke away and melted through the bulb.
I consider this improbable and at most very rare, since I have yet to
hear of this or experience it, even after spending a goodly chunk of my
youth as "The Mad Lamp Abuser"!
Having a burned out lamp (lightbulb) with an actual melted hole showing
signs of being made by an exiting small hot object sounds like strong
evidence to me. If I ever had such a thing, I would find a way to make an
arrangement to loan it to the manufacturer so that they can use it for
feedback but then I get back such a rarity. If the lamp was of a brand or
model easily identifiable as subpar, especially if purchased from a dollar
store, then my next move would be to find out if my municipality, county
and state has fire marshalls and report this to every fire marshall
possible. I would also report it to the Consumer Product Safety
Commission.
- Don Klipstein (
[email protected])