What's this lightbulb?

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.
Daniele
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On Monday, 14 January 2019 07:12:58 UTC, D.M. Procida wrote:

It's just old. Intended to go in a floodlight. In days of yore they couldn't make reliable thin tungsten filaments so they had to be long. It IS interesting.
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Even today they don't make reliable filaments either, long or not. I have a couple of display cabinets with the filament strip lights behind a baton. although the filaments are supported every inch or so along the tube they used to fail very fast. I now run two in series which I'm told gives off a nice golden light which makes the crystal sparkle better. Brian
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So likely to be a high-powered, standard mains voltage bulb?
I assume it would not come to any harm run at a lower voltage, though I know that some lamps can darken as the result of deposits on the inside of the glass when run dimmed.
Daniele
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On 14/01/2019 09:31, D.M. Procida wrote:
<snip> > So likely to be a high-powered, standard mains voltage bulb?
If it is mains, there probably wasn't a 'standard' supply voltage when it was made.

Cheers
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Clive

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On Mon, 14 Jan 2019 10:31:56 +0100, snipped-for-privacy@apple-juice.co.uk (D.M. Procida) wrote:

The darkening is metal vaporizing from the filament and settled on the glass. The bulbs that habe a mechanisnm to avoid this are the halogen bulbs: the glass is run hot, a halogen scrubs the metal off the glass, and re-deposits it on the filament.
This is positively not a halogen bulb -- run it with as low a voltage as you like.
The lifetime of a lightbulb is exquisitely sensitive to to voltage, something like (voltage/ratedvoltage)^-12 to (voltage/ratedvoltage)^-14. So running a bulb at 99% of the rated voltage will increase its life by 12-15%.
Thomas Prufer
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On 14/01/2019 11:02, Thomas Prufer wrote:

There was a "fashion" (in the late 80s I think) for cars to have dim-dipped lights - in fact I think it was a legal requirement at one time - where, with the ignition on and sidelights on, the headlamp bulbs were connected in series (for more light in dusk I assume). This was supposed to have shortened the lives of the halogen bulbs used at the time.
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Max Demian

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Common on London taxis - but they used the all in one Lucas sealed beam unit, which wasn't halogen.
These days that same unit on full looks like dim dip.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 14/01/2019 11:02, Thomas Prufer wrote:

When I moved to my current house in 1991, the bathroom had one of those nasty fittings with three 40-watt reflector bulbs that gave out rubbishy illumination.
I replaced it with a standard BC fitting and stuck in a 60-watt clear Woolworths bulb as a temporary measure so I could see what I was doing when shaving. (bulb marked 240 volts).
It's still there and working fine.
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On 14/01/2019 07:12, D.M. Procida wrote:

"Let There Be Light"
Looks to be an old cylinder filament bulb - c.f. modern versions such as
https://www.hollowaysofludlow.com/shop/lighting/bulbs-cables-and-fittings/bulbs/vintage_cylinder_filament_bulb

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Robin
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     snipped-for-privacy@apple-juice.co.uk (D.M. Procida) writes:

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.
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.)
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Andrew Gabriel
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On 14/01/2019 09:12, Andrew Gabriel wrote:

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.

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Robin
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On 14/01/2019 09:33, Robin wrote:

If you zoom in on the photo, you can see that this filament is coiled quite loosely.
A modern tungsten filament bulb is double-coiled, ie the wire is wound into a very fine spiral, and then that spiral is coiled again.
https://qph.fs.quoracdn.net/main-qimg-cf5603e8a8d9b23cd3d3a0ca379faa72
https://www.quora.com/Why-does-the-filament-in-the-coiled-shape-in-the-tungsten-bulb-produce-more-light
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On 14/01/2019 11:21, GB wrote:

My terminological failure: I grew up with "coiled" as shorthand for coiled-coil, never having met a lamp that was a _single_ straight wire. Indeed, ones like Daniele's which clearly has the filament passing up and down were sometimes called "straight wire".
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Robin
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The squirrel cage filament lamps were not coiled, but had a significantly longer filament than the lamp in the picture.
The double-ended tubular 30W and 60W filament lamps are single coil to make the filament long enough. They are normally vacuum tubes too, as any gas fill has a significant cooling effect on such a long filament and it wouldn't get up to temperature. To compensate for lack of gas fill, the filaments are underrun to avoid the tungsten subliming too fast, but that also makes them horribly inefficient, and they were still only rated 750 hours. Altogether, a bad idea.
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Andrew Gabriel
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On 14/01/2019 15:45, Andrew Gabriel wrote:

Pointed cap donned
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Robin
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It is indeed coiled.
Daniele
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Squirrel cage lamps were for many years the std fitment for ships navigation lights as they gave a nice even light distribution, they often move around a fair bit especially at the top of a mast so I don’t think they were that fragile.
GH
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On Mon, 14 Jan 2019 08:12:54 +0100, snipped-for-privacy@apple-juice.co.uk (D.M. Procida) wrote:

Possibly a decorative low current lamp such as these modern version.
https://www.lightingstyles.co.uk/e27-30w-large-tubular-filament-amber-lamp
https://www.dowsingandreynolds.com/shop/vintage-light-bulb-tube-long-filament/
The filament usually only glows, you can see the amount of slack in them, anything much more than the power needed to make them glow would also make them expand, sag and break.
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On Mon, 14 Jan 2019 08:12:54 +0100, snipped-for-privacy@apple-juice.co.uk (D.M. Procida) wrote:

Could it be for a cine film projector?
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