Carbon filament lamps. Any use?

[Tractorfan]

Hi,
I've accumulated a few (some NOS) carbon filament lamps recently and I was wondering if they'd have any practical use in these days of halogen, CFL and LED lighting? Also, every lamp I've seen so far has been a bayonet cap type, except for a reproduction one I bought in Florida which was ES.
I realise that they probably chuck out more heat than light. Would they be any good in lamp limiters?
Cheers, Pete.

[Herald1360]

Not much use for a lamp limiter- carbon has a negative temperature coefficient, so higher resistance cold than hot.

You might be able to play with one and make a low frequency oscillator for fun but otherwise I think decoration would be the best use.

[emeritus]

Old books that describe lamp boards for charging accumulators from DC mains, said that carbon filament lamps should be used. I was surprised at this in view of their negative temperature coefficient, but perhaps it was a matter of cost, as carbon filament lamps were considerable cheaper than tungsten in the inter-war years. Perhaps it was desirable to back off the current as full charge was approached rather than aiming for constant current?

I did buy a modern reproduction carbon filament lamp (BC, but ES was also available) when my local B&Q stocked them a few years ago, and it was certainly not cheap. They also stocked reproduction vintage tungsten filament lamps of the non-coiled filament type where the filament zig-zagged between upper and lower supports, but I didn't get one of those.

[JacKam_]

Pete, as you said - more heat than light. If you took the attached picture of your house - I would not recommend them. Try some warm LED lights instead.

[broadgage]

In view of the low efficiency, carbon filament lamps have little application these days for everyday lighting.

They are however very decorative and to my eye at least look rather pleasing in a period or traditional interior. The reduced light output and the light being emitted from a large area means that bare lamps are more acceptable than with tungsten lamps.

The other main use is as a low intensity heat source especially for the rearing of tropical animals. A couple of 60 watt tungsten lamps in a reptile enclosure might produce excessive glare, but a couple of carbon lamps would be fine.

Carbon lamps can be used in a lamp limiter, a 240 volt, 60 watt carbon lamp will limit the current to 250ma just as a similarly rated metal filament lamp would.
The voltage/current characteristics of carbon and metal lamps are very different, but this is of surprisingly little consequence in practice.
A metal filament lamp is arguably better for a lamp limiter due to the low voltage drop at low currents.

Carbon lamps are very resistant to vibration, among the last large scale uses were for lighting signals on the London underground, and for task lighting on high speed newspaper printing presses.

Demostrate the magnetic field generated by the fillament, simply hold a magnet near the globe and the fillament shakes around (assuming you are using AC!).

[ex 2 Base]

If the filament is a coil they can be used to locate the polarity of DC machines pole pieces when the machine motor or generator are actually in use. If the lamp filament is a coil and the lamp is energised using DC of the appropriate voltage, then one end of the coil will be Pos and the other Neg.We had a blob of RED paint on the Pos side of the lamp. You have to a bit careful not to stretch the filament to far otherwise it breaks. Not a Radio related of course.Ted

[emeritus]

If any of them are really old, they may well have Platinum lead-in wires, as this was the only known metal that had a coefficient of expansion the same as glass before Dumet lead-in wire was invented. So even a broken lamp could be useful for its Platinum.

[Brigham]

I use them wherever the bulb is exposed to view. They are particularly pleasing in my later kitchen extension, as they don't overpower the incandescent gas in the original rooms.

[hannahs radios]

If those lamps are really a hundred years old they are true antiques yes fire them up from time to time but I think they will be worth more preserved in working order. I have seen those repro ones in lots of bars round here they look really nice. It's always nice to see real bulbs in use instead of LED and CFL rubish

[ColinTheAmpMan1]

Originally Posted by Brigham

they don't overpower the incandescent gas in the original rooms.

Good grief! How do you cope with incandescent gas in your rooms? It sounds quite hazardous.
Colin.

[broadgage]

Originally Posted by Brigham

I use them wherever the bulb is exposed to view. They are particularly pleasing in my later kitchen extension, as they don't overpower the incandescent gas in the original rooms.

Splendid, sir, absolutely splendid.

[AC/HL]

Please keep on topic.

[seymour32]

Very nice looking , these are back in fashion now as they are being used by some interior designers. With specialist manufactures reproducing them again, they now seem to be called Squirrel Cage Lamps.

[russell_w_b]

Originally Posted by merlinmaxwell

'...simply hold a magnet near the globe and the fillament shakes around (assuming you are using AC!)...'

You can do this on an ordinary coiled-coil tungsten filament lamp: a clear one is best. An ALNICO magnet from a type 26A telephone magneto held near the bulb offers spectacular results!

[Ian - G4JQT]

If you have no use for them why not put them on ebay with some good photos, especially of the base?

As some have said here, they are decorative and I saw a similar (expensive!) range in a wood-burner stove store last year - although they may not have been carbon filament, they were decorative with very big, yellow curly filaments visible though the clear glass bulb.

They may be inefficient when it come to making light from electricity, but the heat they produce theoretically means you don't need the central eating on so high. And the lights are on mostly in the winter when it's dark and cold!

Ian

[broadgage]

Originally Posted by seymour32

Very nice looking , these are back in fashion now as they are being used by some interior designers. With specialist manufactures reproducing them again, they now seem to be called Squirrel Cage Lamps.

Squirrel cage lamps and carbon filament lamps are not usually the same thing, though often confused.
A carbon filament lamp uses a relatively short and thick filament, formed into either a loop or a large coil of only a few turns.

A metal filament lamp needs a much longer* and thinner filament. In the early days of lamp manufacture, the only way of fitting such a long* filament into a reasonable size bulb was in a vertical zig zag arrangement.
Such lamps are still manufactured for decorative and other purposes and are very often wrongly described on auction sites as "carbon filament"
If you search on an auction site for "carbon filament bulbs" most of the results will in fact be vintage style metal filament lamps.

If in any doubt if a certain lamp is carbon filament or an old style of metal filament, then the answer may be determined beyond all doubt by measurement.
Measure the cold resistance of the lamp with a test meter. Calculate the hot resistance from the lamp wattage and voltage.
If it is a metal filament lamp then the cold resistance will be lower than the hot resistance.
If it is a carbon lamp, then the cold resistance will be higher than the hot resistance.

Both true carbon filament lamps and vintage style metal filament lamps have their place in a traditional, vintage or period interior.

*Modern metal filament lamps also have a long filament, but it is tightly coiled, and sometimes the coil is again coiled. Such filaments are therefore compact, but still contain a surprising length of wire.

[murphymad]

Carbon bulbs give a very nice light in bedrooms when all you need is a warm low level.

I use vintage (probably 60 to 80 year old) lamps in wall lights.

With the generally low voltage we have on overhead power lines, I suspect they will last many years, then I will have to plug in some more.

Mike...