On 14/01/2019 09:12, Andrew Gabriel wrote:
In article ,
(D.M. Procida) writes:
I bought a lightbulb (and a ceramic holder and rotary lightswitch) in a
second-hand shop yesterday. They had many beautiful items taken from an
old electronics teaching laboratory - all brass, steel, ceramic and
wood.

The lightbulb:
https://www.dropbox.com/s/qw0vnqdtvemf0ld/lightbulb.jpg?dl=0.

It's about 10cm tall, and has an Edison screw. The filament loops up and
down the bulb in six lengths. It's made by Osram, but there are o other
readable markings on it.

Any idea what the purpose of a lightbulb like this might be?

I'm tempted to run it at low voltage to see what it looks like
illuminated, but I'd hate to damage the filament.

It was a standard physics laboratory supplies lamp, used to make
an image of the filament in things like pin-hole viewers/cameras.

It might not be mains voltage. If it's an uncoiled filament, it
isn't long enough. If it's a single coiled filament, it might be.

I thought hairpin style filaments weren't coiled - hence the tubular
design (up to at least 8 inches long IIRC) to make them long enough.


Measure the filament resistance with a test meter.
V^2/(resistance * 15) will give you the approx power rating
assuming a tungsten filament. (The times 15 is to correct for the
temperature change when running, although it may be too high a
factor for such a stretched filament lamp.)

It is sort of mimicing the original squirrel cage filament lamps,
but those were far too fragile to be used in a lab where they
would likely be moved around.

The other type of lamp used for this were carbon filament lamps,
but the filament in yours is far too long and floppy to be a
carbon filament lamp. (They are usually 2 - 4 loops, unsupported.)



--
Robin
reply-to address is (intended to be) valid