The 107 year old light bulb!

[MilDoc]

Anyone see this on NBC news tonight?

A light bulb burning continuously for 107 years!

Why can't I buy one of these? Company went out of business.....

[Alex Franke]

Was that the one in a firehouse somewhere? I read about that quite a while ago... I guess it's true that they don't make things like they used to. . . .I have an old Emerson radio from like the 40's that still works like a charm. Well, mostly.

[LCHIEN]

Anyone see this on NBC news tonight?

A light bulb burning continuously for 107 years!

Why can't I buy one of these? Company went out of business.....

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.
So take a 75W bulb rated for 2000 hours at 120V and run it at 30 volts you'll increase its life by 4 x 4 x 4 x 4 x 4 or a factor of 1024, which would be 233 years.

We could do that with any incandescant light bulb but the output is weak ( a lot less than 1/4 of 75W bulb normal output) and the color very reddish so its very inefficient with power and ugly in coloration so we don't do it except to amuse people with how long we can burn a bulb to get your twenty-five cents worth.

We could also run the bulb at higher voltages but then it burns out very rapidly (similar but inverse exponential ratio applies) so the rated voltage is just the best compromise between life and performance and efficiency.

You can buy the double life bulbs, read the package, for same 100W you will get about 20% less lumens (light output). The reason? Its actually like a higher voltage bulb (130V) run at 120V to get longer life. The double-life bulbs should only be used where getting to and replacing them is extremely inconvenient or costly.

The thing I find amazing about incandescant bulbs is, we spend 25 cents for the bulb, then we spend something like $20 in electricity to light the bulb for its life*. That's why the current push for CFLs.

*A 100W bulb with an 1800 Hour expected lifetime and electricity at 12 cents per KWH = $21.60 to run it for 1800 hours.

Correction: Wiki says that lifetime effects goes as the voltage ratio to the 16th power. Not 5th power as I stated earlier. That means operating between 2/3 or 1/2 voltage would give lifetime lengthening effect I was describing earlier, not 1/4 voltage.

[Tom Slick]

Sure Loring, use facts to ruin mystery...

j/k

[MilDoc]

Well, you lost me. That's why I'm a doctor. SO much simpler!

[leehljp]

Well, you lost me. That's why I'm a doctor. SO much simpler!

LOL! And two OTC aspirin are a lot cheaper too!

[crokett]

Thanks for the explanation Loring. So if I just put all my lights on dimmer switches and get used to the dark the bulbs will last longer?

[Tom Slick]

0 volts makes them last realllllllly long!


side note:
some cheap "long life" bulbs are actually rated at 130v, the "long life" comes from the explanation Loring gave. They'll be significantly dimmer then the standard 120v rated bulb you are replacing. you have to pay attention to the packaging. light output and applied voltage are not on a linear scale.

[kirkroy]

0 volts makes them last realllllllly long!

Until you trip over the box in the dark and break all the bulbs...

[L. D. Jeffries]

Read or saw this somewhere: It's the turning on and off that kills the filaments in bulbs. "They" shot some ultra-high speed film of the filaments when the voltage hit it... the filaments vibrated like a hula dancer. THATS what kills it. So I can see that leaving a bulb turned on would increase its life mucho!

[MilDoc]

And increase your electric bill, I guess.

[eccentrictinkerer]

Read or saw this somewhere: It's the turning on and off that kills the filaments in bulbs. "They" shot some ultra-high speed film of the filaments when the voltage hit it... the filaments vibrated like a hula dancer. THATS what kills it. So I can see that leaving a bulb turned on would increase its life mucho!

The inrush current to a cold incandescent filament can be 15 times the operating current (the first few cycles). A 100 watt bulb nomally pulls 0.833 amps at 120 volts. The inrush current can be 12.5 amps (again it's for a very short time). That makes your light bulb a 1500 watt flame-thrower for a few milliseconds.

That's the main reason a light bulb usually fails just as you turn it on.

[LCHIEN]

Well, you lost me. That's why I'm a doctor. SO much simpler!

OK, Doc, here's the analogy: Give a kid a long term diet of speed and heroin, his BP will be 180/120 and his heart rate 130. and he'll live to be 25 Y.O., maybe.

[LCHIEN]

Thanks for the explanation Loring. So if I just put all my lights on dimmer switches and get used to the dark the bulbs will last longer?

0 volts makes them last realllllllly long!

exactly...

[LCHIEN]

The inrush current to a cold incandescent filament can be 15 times the operating current (the first few cycles). A 100 watt bulb nomally pulls 0.833 amps at 120 volts. The inrush current can be 12.5 amps (again it's for a very short time). That makes your light bulb a 1500 watt flame-thrower for a few milliseconds.

That's the main reason a light bulb usually fails just as you turn it on.

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 150 ohms but instead it really measures closer to 10.
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.


P.S. In fact, just reading wikipedia, tradeoff is made between adding supports to reduce the vibration from mechcanical shock and fewer supports. Seems the more supports reduce life due to the temperature-reduction at the points of support. So current bulbs are a compromise between wearout and burnout. Rough service bulbs are then compromise for more mechnical shock and on-off cycles vs. shorter bulb life.