Draping edison bulbs?

[richardash1981]

No they are NOT carbon filament lamps, despite the claim made by the supplier. "carbon filament" these days seems to mean "old looking" and NOT made of carbon.

The lamps are passable imitations of early types of tungsten filament lamp, in which the considerable length of filament is arranged in a zig zag formation up and down the bub. In modern tungsten lamps the filament is coiled and much more compact.

OT, but do you have a source for not being made of carbon? I seem to remember in the aftermath of the first round of EU lighting energy efficiency rules, some enterprising manufacturers started production of non-tungsten carbon filament lamps, having realised that that rules barred Tungsten Filament lamps but did not bar other sorts of (long obsolete) filament lamps, despite terrible efficiency. The arrival of "LED filament" lamps has largely suppressed the idea, but I can't help wondering what the filament in obviously filament lamps like these is made of. If you zoom the picture it's clearly not an LED line!

 

[adam2]

I have two sources for my statement that most so called carbon filament lamps do not contain actual carbon filaments.

 

Firstly my knowledge of electric lamps and the manufacture thereof. For a mains voltage lamp, a carbon filament is relatively short and only requires forming into a few large loops to fit into the bulb. Tungsten has a much lower resistance than carbon and therefore requires a complex arrangement to fit this long filament into the vintage style bulb. In a modern tungsten lamp this filament is coiled to render it more compact. The thicker carbon filament is much more visible than the very fine tungsten filament.

 

Secondly, basic physics permits of determining the difference between carbon and tungsten filaments by simple measurement. Measure the cold resistance of a lamp and then calculate the hot resistance from the lamp rating. As an example consider a 240 volt, 60 watt lamp. This will draw about 0.25 amps when lit at nominal voltage. That suggests a hot or working resistance of about 1000 ohms. Now measure the cold resistance of the lamp. A 240 volt, 60 watt carbon lamp will have a cold resistance of MUCH more than 1000 ohms. A 240 volt, 60 watt tungsten lamp will by contrast have a cold resistance MUCH lower than 1000 ohms.

 

No great accuracy may be claimed due to manufacturing tolerances, mains voltage variations and imperfect instruments, the difference in the cold resistance between carbon and tungsten lamps of similar rating is however very substantial and will swamp the above factors.

 

Carbon lamps are also of very low efficiency and for a given wattage will be much dimmer than even a vintage style tungsten lamp, which is itself dimmer than a modern tungsten lamp.

 

60 watt carbon lamp=about 120 lumens.

 

Vintage style 60 watt tungsten lamp=about 400 lumens

 

Modern 60 watt tungsten lamp=about 800 lumens.

 

 

 

 

 

OT, but do you have a source for not being made of carbon? I seem to remember in the aftermath of the first round of EU lighting energy efficiency rules, some enterprising manufacturers started production of non-tungsten carbon filament lamps, having realised that that rules barred Tungsten Filament lamps but did not bar other sorts of (long obsolete) filament lamps, despite terrible efficiency. The arrival of "LED filament" lamps has largely suppressed the idea, but I can't help wondering what the filament in obviously filament lamps like these is made of. If you zoom the picture it's clearly not an LED line!

 

 

To be strictly accurate, it was not the manufacture or import of TUNGSTEN lamps that was prohibited, it was the manufacture or import of electric lamps with less than a stated efficiency.

 

The lamp linked to is clearly a tungsten filament lamp. Note the long and extremely fine filament.

 

 

 

 

 

[DrV]

adam2, thanks for that - very interesting. And I'm glad I remembered the physics lesson correctly. Mr. Bullimore would have been proud!

[richardash1981]

Again, thanks Adam. I didn't know about the vastly different temperature coefficients of resistance for carbon and metals. In the table I looked at, only Carbon, Silicon and Germanium have negative temperature coefficients of resistivity - i.e. the resistance goes down when they heat up, as Adam explained. All the metals have various positive values, so higher resistance when hot. Makes a conclusive case that no amount of clever manufacturing techniques to manipulate the length/thickness/strength can defeat.

 

Presumably this means that carbon filament lamp lasts much better with a thermo-mechanical flasher (like a car turn indicator or belisha beacon) than a tungsten bulb, because there is no inrush shock each time it switches? Was this part of the reasoning for using them in signals on the Underground (which must switch on and off a lot) as well as vibration from the trains?

 

[adam2]

Carbon lamps undoubtedly withstand vibration much better than metal filament lamps, for that reason they were favoured until recently for engineers inspection lamps, on high speed printing machinery, and on warships. I would expect that they would also stand up to frequent switching well. BTW the lamps in older underground railway signals were lit continually (oil lamps originally) A compressed air mechanism pushed a green or yellow lens in front of the lamp, absence of the air supply caused a red lens to drop by gravity in front of the lamp.

 

Metal filament lamps in the lower voltages stand up well to vibration. The main alternative to mains voltage carbon lamps was a 6 volt vehicle lamp worked via a transformer, presuming an AC supply. A carbon lamp was cheaper and simpler.

6 volt and 12 volt turn signals on vehicles survive well. 24 volt less so.

 

Carbon lamps for general lighting of homes and workplaces "went out with the (second) war" but were still used for certain purposes as described.

[mk_193]

You mentioned this is a school production, which has me a bit uncomfortable about some of the suggestions being made that involve cobbling stuff together with junction boxes.

 

Are you a drama teacher or a pupil? Knowing that and a rough budget will allow more accurate suggestions for what you wish to achieve.

 

Before shipping I did independently verify - the OP is a staff member and definitely not a student.

 

I work as a technician in the arts centre we have at the school, but my knowledge of practical wiring and electrics is limited. We have a maintenance department I get on well with so am going to get their assistance in making these!

Got the junction boxes in the post, so thanks very much for those

 

Interesting stuff about the carbon lamps too!

[adam2]

Update to this, metal filament lamps are still being sold on fleabay as "carbon filament" but numbers have been reduced from hundreds to dozens. Possibly because I have been reporting incorrect listings.