4v 0.75a osram small edison screw bulbs

[Marks n Sparks]

I have a couple of these bulbs and cannot find what they would have been used for. At 4v i would expect them to have be used with an old 2 cell accumulator like a miners or railway lamp but why such a large thread? They have a small slightly mushroomed envelope, about the size of the small car/motorcycle indicator but mushroomed. I haven't been able to identify there use by searching the internet, apart from curiosity it would seem a shame to bin them if some one some where could use them. Anybody any ideas?

[Mónico González]

Hello.
I realize this is a little old post, but till today I've not read it.
I guess as you have said, that this lamps must be for mining lighting purposes. In fact, miner's helmet lamps works usually on that electric values because as you've said also, the source commonly used even to our days for mining lamps have been the classic two cell 4v lead battery or its "nearer" 3,6v Ni-Cd or Ni-MH 3 cell counterpart, so, that standard voltage of miniature lamps for that use.
About the extra lenght of its threaded cap, I couldn't say nothing, because I must see at least a picture of your particular bulbs, but I guess it could be done with the purpose of avoiding the unscrewing the whole lamp while on service due to vibrations, shocks or dropping of the reflector head directly to the floor. I've been using standard miniature mining lamps often during many years (and I'm still doing it), but all of them has the classic miniature SES cap, or E10 as here in Europe is known, exactly the same used for regular consumer flashlight and lanterns for household use. The main difference about both kind of bulbs is their nominal current consumption, that is greater for mining lamps, usually from a minimum of 500 mA for "short range light" and at least 1A for "long throw" concentrated beam. Most of times newest regular filament mining lamps are gas filled, not vacuum as for regular use flashlight ones, but in the later times of incandescent portable mining lighting before the coming of LED's, those lamps used to be of quartz-halogen type.
If you are interested about this issue I suggest you could post some pics of them, please.
Regards.

[adam2]

Quite possibly a bulb for a miners cap lamp, but two other possibilities occur to me.
Firstly, perhaps an exciter lamp for a movie film projector, not of course to project the image but for sound reproduction. Many movie films had an optical sound track, through which light from a small lamp was passed and partially obscured before being detected by a photocell and amplified to produce the audio signal. To avoid any mains hum being superimposed on the audio, exciter lamps were usually operated at high frequency from a valve oscillator, this being simpler than producing smooth DC.

Alternatively it might be a lamp for lighting a microscope or a reflecting galvanometer. Such instruments often used odd lamps, I suspect to stop people using cheap torch bulbs or vehicle bulbs.