240 volt light bulb

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boltneck

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ok so i install a new lighting fixture for a customer today

its a pendant type fixture with a clear glass shade arts and craft style they bought online

the bulb they sent with it was an antique look old carbon filament style but was 100 watt 240 volt

so i told her they sent the wrong bulb and put in a regular a lamp 60 watt

her husband gets home from work and calls and says they really want the old look lamp. i told him it would be only half wattage if used and i think they should exchange them for the proper voltage

he says they sell them like that to get the old dim look

does anyone see a problem with them using the 240 volt lamps?
 
raider1

raider1

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Staff member
Location
Logan, Utah
I have used the same thing in the past.

If you run a 240 volt light bulb at 120 volts the bulb will be much dimmer and looks like an old gas light.

I installed these bulbs in a light pole for a customer because the wanted the look of an old gas light pole.

Chris
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
090612-2220 EST

Somewhat more correct values for a tungsten filament bulb using a 100 W 120 bulb are:

100 W bulb rated for 120 V

120 V 0.84 A 100.8 W 143 ohms
060 V 0.57 A 34.2 W 105 ohms

A tungsten filament lamp is not a constant resistance device over the voltage range from 0 to full rated voltage.

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C

charlietuna

Senior Member
Thats what we used for voltage testers before they made wiggies! Dim was 120 volts--bright was 240 volts!!!:D

They were used in traffic signal lights!
 
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broadgage

Senior Member
Location
London, England
gar said:
090612-2220 EST

Somewhat more correct values for a tungsten filament bulb using a 100 W 120 bulb are:

100 W bulb rated for 120 V

120 V 0.84 A 100.8 W 143 ohms
060 V 0.57 A 34.2 W 105 ohms

A tungsten filament lamp is not a constant resistance device over the voltage range from 0 to full rated voltage.

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Click to expand...

I believe that you are correct, if the voltage on a tungsten filament lamp is reduced, then the filament runs cooler, and as a consequence has a lower resistance.
A lower voltage on a lamp will allways result in less current, but not in proportion to the reduced voltage, in the above example the half voltage reduces the current from 0.84A to 0.57A, and not to 0.42A as might be expected.
However all this refers to TUNGSTEN filament lamps, whereas the O/P refers to a CARBON filament lamp, which has a different change of resistance with temperature. The resistance of a carbon lamp increases at a lower temperature, therefore if worked at half voltage, the current drawn will be much less than half. As a result the reduction in light output on half voltage will be even greater than with a tungsten lamp, and probably useless.

The options would therefore appear to be accepting a 120 volt tungsten lamp, or obtaining 120 volt carbon lamps, which I believe are still manufactured.

As a last resort it might be possible to fit a transformer in the fixture to increase the voltage to 240.
Although code does not permit a 240 volt supply to the fixture, an internal transformer might be acceptable. After all, some flourescent fixtures use a lot more than 120 volts accross the lamps, and no one worries about that.

Carbon filament lamps in 120V may be obtained from the KYP GO company,http://www.kyp-go.com/default.htm
 
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iwire

iwire

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Staff member
Location
Massachusetts
broadgage said:
The options would therefore appear to be accepting a 120 volt tungsten lamp, or obtaining 120 volt carbon lamps, which I believe are still manufactured.

As a last resort it might be possible to fit a transformer in the fixture to increase the voltage to 240.
Click to expand...

Or we could just use the lamp the customer wants, the same one supplied with the fixture and move on. :cool:


BTW we can not supply a that fixture with 240 regardless of the fact fluorescents operate at much higher voltages.
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
090614-0806 EST

broadgage:

In the original post reference was made to
"the bulb they sent with it was an antique look old carbon filament style but was 100 watt 240 volt",
but it did not say it was a carbon filament, just style. Probably meaning a non-frosted bulb. I believe it would be difficult to make a small 240 V carbon filament. My guess is that Edison settled on about 110 V for his distribution system based on the practicality of making the filament.

For plots and photos relating to tungsten, carbon filament, and fluorescent lamps see
http://www.beta-a2.com/EE-photos.html
photos P9 thru P18.

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B

boltneck

Member
yes it was a tungsten "loop" lamp

to give the "look" of an old carbon filament lamp

and yes i was wrong that i told her it would only be half wattage as JFletcher stated it would only be 25 watt

anyway i recommended that they return the 240 volt bulbs and get the 120volt version of the same bulb
 
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Cold Fusion

Senior Member
Location
way north
boltneck said:
---anyway i recommended that they return the 240 volt bulbs and get the 120volt version of the same bulb
Click to expand...
I 've followed this clear through - I still don't understand why you recommended they get a 120V version. As iwire pretty well said, why is what they want bad or wrong?

cf
 
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broadgage

Senior Member
Location
London, England
There is nothing wrong or dangerous about lighting a 240 volt lamp on a 120 volt supply, but it will be extremely dim, and probably wont meet the customers needs.
If this is a tungsten lamp, then at half voltage it will use roughly one third of its rated wattage, but that wont be one third of the light output.
A tungsten lamp worked at half voltage gives about 7% of it rated light output, which may not meet the customers needs.
If it really is a carbon filament lamp, then at half voltage the light be a lot less then 7% and almost certainly useless.
 
raider1

raider1

Senior Member
Staff member
Location
Logan, Utah
but it will be extremely dim
Click to expand...

I will bet that is exactly what the owners want. I will bet the owners want a dim lamp for a specific look. As I pointed out earlier I have used 240 volt lamps on 120 volt to get the look of an old style gas light. The effect worked very well and my customers were pleased with the end result.

Chris
 
B

boltneck

Member
Cold Fusion said:
I 've followed this clear through - I still don't understand why you recommended they get a 120V version. As iwire pretty well said, why is what they want bad or wrong?

cf
Click to expand...



"why is what they want bad or wrong?" its not at all, i just assumed they sent the wrong bulbs. so i put in clear 60 watt 120 volt bulb, told her to exchange the ones they sent for 120 volt, got paid and left.

her husband called later and said he wanted the "look" of the old bulb they had sent. so i told him to try it and if it was too dim then they could get the old "look" bulb in 120 volt, whatever wattage.

sorry to be confusing. the homeowner had no idea of the voltage or wattage, they were only after the old look of the looping filament bulb
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I would recommend trying what the customer asked for first, and if they're too dim, 120v bulbs and a dimmer.
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
090615-`1811 EST

My plot in photo P9 would indicate that the light intensity at 50% voltage would be about 15% of the full voltage intensity.

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