Re: How do Philips X-treme power bulbs work?

In article <meSFk.60643$Mh5.48444@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
"TKM" <nomail@xxxxxx> writes:

"Travis Evans" <travisgevansQ@xxxxxxxxx> wrote in message
news:8CLFk.236$OY7.165@xxxxxxxxxxxxxxx
On Sat, 04 Oct 2008 14:52:17 GMT, TKM <nomail@xxxxxx> wrote:
Shaking and/or sharply tapping a small C7 or C9 line-voltage lamp does
sometimes "repair" it. What happens is the broken ends of the filament
swing around and if they happen to touch, the arc which is generated
welds
the filament pieces together. The weld is weak and it's likely that the
filament is now shorter than before, so the lamp burns brighter before it
fails agan. But, it can burn for many hours. I've done such a repair on
holiday lamps many times with no nasty results; but, of course, the lamp
can
break if hit too hard and there's a small chance of the filament arcing
into
the lamp base through the filament support wires.

This reminds me of a history article on a streetlamp collector's website
about incandescent streetlights in the early days. Many of these at
the time were in series circuits where the voltage of a circuit with
many lamps could easily be in the hundreds or even thousands of volts.
It mentioned that often a series lamp with a breaking filament would
be welded back together by the high-voltage arc and that this would
often happen to the same lamp repeatedly over time. The article said
that the effective filament length would become shorter and that these
lamps would become dimmer and redder instead of failing to light
altogether.

That's a great example since no matter how short the filament, the same
current would go through it and the lumen output of the lamp would be a
function of the length of filament remaining. The redder output results
from the reduced lamp wattage and lower filament temperature.

A council lighting engineer gave me a dead one of these lamps.
It was rated 300W 5.5A IIRC, but no voltage specification, being
designed for series operation. I was told it has something in the
lamp base which shorts out when the filament breaks and a few
thousand volts appear across it, so the others stay on (a bit like
fairy lights). They stopped being able to obtain the series filament
lamps sometime before 1970 and had to swap them out for mercury
vapour lamps whose control gear was designed to run on a series
circuit. (In the mid-late 1970's, those were all changed to LPS
lamps, but I think the series wiring was abandoned at that point.)
Some years later, I saw the series loop power supplies in the
basement of the town hall, although it was no longer used at that
point. Quite fancy constant current transformers which had a core
which moved depending how many lamps were shorted (someone had
marked the core positions for various numbers of dead lamps).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
.

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