BBob    (smile, yer on PICList too)


>As an auto mechanic, I use dayly what is known here as a "drop light". It's
a
>100W rough service bulb with caged handle and recoil cord storage. On many
>ocasions my "drop light" has done just that. Usually I will hear a pop,see
>smoke, and make a suitible remark about the loss. On some occasions
however, my
>light will, after hitting the deck,  gain intensity and the colour seems to
>change to a whiter radiance. Is this apparent blue shift due to an arc or
other?


This is the "super lamp" I was talking about from exactly the same
situations in my youth.
What happens is the filament breaks and the loose ends swing fee and manage
to touch a place on the other end of the filament thereby providing a
shorter path than originally. The current flow provides localised heating
and tacks the filament into its new position. The shorter filament has a
lower resistance hence higher current flow hence more energy dissipated
hence higher temperature. The higher colour temperature produces a whiter
light. The higher power produces a brighter one. Once this happens, turn it
off, carefully take out the bulb, tiptoe to the nearest fixed downwards
mounted light fitting and place the bulb therein. It will run happily as a
super lamp for from weeks to about 1 second.

We used to make these if we could after a filament break by peering into the
dead lamp and moving it so as to bring the loose ends into contact with part
of the filament on the other side of the gap. Lamps with longer filament
runs lend themselves to this.
Haven't done this for some while now. Must be getting old :-)



RM

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