More Odd Bulbs.

[HamishBoxer]

One of these two are marked is marked 10Volts 240 Watts.The other is very similar but unmarked.

Ex fairground? I await with intrest any comments.
Thank You David

[Refugee]

Movie projector?

[HamishBoxer]

Could be though 1930,s I guess.

[TonyDuell]

Some random speculation...

240W is too low a power for a cinema projector (which at that time probably used carbon arc lamps). It's about right for a domestic projector, but most of those used a 110V or so bulb with a series resistor and not a step-down transformer (possibly due to the use of DC mains in some areas).

The base of those bulbs suggests they were designed to be accurately positioned (as opposed to a screw cap) in an optical system, perhaps a reflector or condensor lens type thing. I doubt they were for general illumination use.

10V is also odd, it doesn't suggest running off a car battery or other vehicle battery. On the other hand, taking 24A suggests either a lead acid battery (5 cells?) or a transformer as the power source.

Some kind of small portable-ish spotlamp?

Is that 'BTH' on the base? Britiish Thompson Houston ?

[Colinaps]

Signalling lamp? It's not the same flange or filament arrangement as an Aldis but nevertheless... And using a 10V bulb at 12V would give a faster response - possibly the filament arrangement is to absorb the mechanical stresses of repeated off-on cycles?

Cheers,

Colin.

[G6Tanuki]

Low-voltage high-current bulbs were often specified for things like ships' navigation-lamps because their thick filaments were relatively robust so more-immune to the shocks of traversing stormy seas (and, in the case of warships, the effects of firing serious-calibre guns!).

[dseymo1]

I'd certainly say they were part of an optical system of some sort, as the filaments are constructed to approximate a point source.

[HamishBoxer]

Just checked with a head magnifier and both are 240W at 10 volts.Cannot see BTH but there a number(s) 5L/1818 on one.

[broadgage]

I think that it is for a signalling lamp.
Such a thick filament wont respond very quickly to on/off switching and was probably intended for the type of signal lamp in which the bulb is lit continually and signalling achieved by a mechanical shutter that somewhat resembles a venetian blind.

A very compact filament is needed to achieve a narrow beam angle which is required for two reasons, firstly concentrating the light into a narrow beam makes it brighter to the intended recipient, and secondly makes it less visible to others such as the enemy in wartime.
Such signalling lamps often incorporate a small telescope to assist in accurate aiming.
Commonly called Aldiss lamps, but that is a trade name and other brands exist.

10 volts is probably for use on a nominal 12 volt circuit, either from a portable battery, the voltage of which will drop under such a heavy load, or to allow for voltage drop in some yards of cable if connected to the electrical installation of a boat or vehicle.

[turretslug]

5L/1818 could well be a pre-NATO UK Forces stock number.

[HamishBoxer]

I am very grateful for all these thoughts and if there are any more please keep them coming.

[camallison]

Definitely from a signalling lamp - I replaced one or two when at gliding school in the air cadets (1963/4). We used the lamps for signalling to the winchman. We had Aldis and other makes, and these were in the "other" makes.

Colin

[HamishBoxer]

Thanks Colin and there I was thinking they were rare and even valuable!They look so 1930's but I guess not so.

[Herald1360]

They're probably a thirties or earlier design. No point reinventing the wheel......

[broadgage]

Possibly valuable to anyone who has an old signalling lamp and wishes to restore it. Naval museum ? anyone with an old ship that they want to keep original perhaps.

Special purpose bulbs tend to be very expensive even when new, replacements for current Aldiss lamps are over £60 each.

"A daylight signalling lamp, not dependant on the ships main electrical system" is still a legal requirement for all ships over a certain size. Anything required by law tends to be expensive.

[HamishBoxer]

I did not think that much.Anyway not thinking of selling them just yet.