The 107 year old light bulb!

[cgallery]

How do we really know the light bulb is that old?

[gerti]

That's true, the filament is a temperature dependent resistor, when you measure a light bulb, if it was truly resistive, a 100 Watt light bulb would measure about 1.5 ohms bt instead it really measures closer to zero.
When you turn it on there's a tremendous rush of amperage, possibly more than the famous inductive motors turn on rush, but it lasts much shorter time. when the element heats up the resistance goes quickly to the operating point.

The burnout over time (I'm guessing) is probably due to oxidation of the element due to trace amounts of oxygen in the bulb, and vaporization of the tungsten filament from boiling off at temperature.
I think light bulbs are designed to withstand the mechanical shock of being turned on and off. Unless you turn it on and off every ten minutes, thousands of times per week, the burnout effect is probably going to exceed the filament wearout due to mechcanical stress.

The turn-on burn out is also largely a timing question, as we are talking AC current. If you happen to switch it on just as the voltage is at it's peak, the effect of the low resistance of the cold filament is hugely exaggerated.

Many years ago I built some custom dimmers for my parents business, where the rather expensive bulbs (special temperature and design) burned out frequently. I wasn't so much after the dimmer capability, but rather after a side effect that that specific dimmer design had a zero crossing detector and would only allow current to start flowing the bulb at that point. That increased the average life of those bulbs about five-fold.

[LCHIEN]

Wiki says:

The relationships above are valid for only a few percent change of voltage around rated conditions, but they do indicate that a lamp operated at much lower than rated voltage could last for hundreds of times longer than at rated conditions, albeit with greatly reduced light output. The Centennial Light is a light bulb which is accepted by the Guinness Book of World Records as having been burning almost continuously at a fire station in Livermore, California since 1901. However, the bulb is powered by only 4 watts. A similar story can be told of a 40-watt bulb in Texas which has been illuminated since September 21, 1908. It once resided in an opera house where notable celebrities stopped to take in its glow, but is now in an area museum.[40]

So, this 107-y.o. bulb operates at very low power/voltage.

[RodKirby]

Why did I read this thread

[leehljp]

Why did I read this thread

Are you bored, Rod?

[rnelson0]

I'm not impressed. There's no magic there.
An incandescant's life is proportional to the something like the 5th power of the ratio of the voltage.

Actually it's what L.D. Jeffries said, it's the turning on and off of lights that causes the filament to break. Assuming no power outages, no siesmic events (on the light bulb's scale), a light bulb should last nearly forever. It's a vacuum in there, so there's little method for the filament to decay. Your 1800 hour bulb (75 days) can easily last a whole year or more just by not turning it off, ever. Once the summer comes around, everyone turns their AC on, and the power goes out, just don't expect that light to come back on.

http://members.misty.com/don/bulb1.html#wbt

It also helps that older light bulbs had typically thicker filaments.