World's oldest light bulb

[Ian E G7OLT]

You've got to wonder how this one has lasted a 110 years, see:-

http://www.dailymail.co.uk/news/article-...ation.html

[fido]

I think early bulbs were often replaced before they actually blew because they suffered from black deposits forming on the inside of the glass.

[beam me up schottky]

Incandescent bulbs can be made to last much longer than a thousand hours and even now ruggedised bulbs can be obtained that will survive 10's of thousands of hours. Obviously the lighting industry quickly realised that long lasting bulbs were not exactly good business for them !
Aviation bulbs are ruggedised for long life and the military have a ruggedised spec for certain applications.
I recall when low energy bulbs were introduced and were claimed to have much longer life than incandescent, in my experience they didn't but I have noticed that the newer types are much better.
Can't help wondering how the history of the bulb in this story can be proved though.

[Skywave]

There appears to be an inconsistency in that report.

Quotes:
Extract 1:
Lynn Owens told Time.com: "Nobody knows how it's possible. It is a 60-watt bulb and it's only turned on for about four watts, but nobody knows why it keeps burning".

Extract 2:
In 1976 it was moved to its present site at Fire Station 6 in Livermore. It was then hooked to a separate power source at 120V, according to Frank Maul, Retired City Electrician, with no interruptions since.

The only answer that I can come up with to explain that apparent inconsistency is that in the second extract, if the bulb is indeed connected to the 120v source, it must be via a substantial voltage-dropping resistor or a triac light-dimmer. However that invalidates the technical merit of the claim.

Al.

[beam me up schottky]

The filament is carbon, modern bulbs are tungsten, hence the difference in thickness.

[Skywave]

Maybe, Jamie, maybe.
I did a few sums. The cold resistance of the light bulb is 240 ohms.

If we assume:
(1) that its hot resistance is twice that, 480 ohms, then the voltage across the bulb is 44 volts. This gives a current in the circuit of 92 mA. Hence, the voltage-drop across the line cord is 76 volts; its resistance is 826 ohms. The power dissipation in that line cord will be in the region of 7 watts.

If we assume:
(2) that its hot resistance is 150 % of that, 360 ohms, then the voltage across the bulb is 38 volts. This gives a current in the circuit of 105 mA. Hence, the voltage-drop across the line cord is 82 volts; its resistance is 781 ohms. The power dissipation in that line cord will be in the region of 9 watts.

So, taking a mean figure of 8 watts dissipated by the line cord, I have to ask: "Is this a reasonable amount of heat that can be tolerated by such a voltage-dropping line cord?" (Especially as this bulb is situate in a fire station? :s )

I strongly suspect that in my first extracted quote, when it was stated "only turned on for about four watts", the person actually meant "only turned on for four hours (per day)". Or that that person was simply mis-quoted. Moreover, why would the installer of this bulb choose to fit a voltage-dropping line cord in the first place, especially since the light output from the bulb will then only be in the region of 4 watts? Hardly an illuminating source!

Al.

[fido]

Whatever dimming method is used I would assume it is to prolong the life of the bulb for the world record attempt. I don't suppose it's light is needed, it is just there as an exhibit.

[Skywave]

O.K., so a light dimmer is (possibly) in use. But surely that invalidates the claim, since that claim is, per se, based on comparisons with other light bulbs running on their full nominal voltage?

Al.

[fido]

http://www.guinnessworldrecords.com/Sear.../63240.htm

[Skywave]

O.K., O.K., so it's a 60-watt bulb running at a dramatically reduced power of 4 watts. And a claim is being made as to this being the world's longest "running" light-bulb. I rest my case as per Post #11.
'Nuff said.

Al.