hi!

i just came across this Guinness world record holder light bulb (through a post on facebook): http://en.wikipedia.org/wiki/Centennial_Light

how is it possible that the bulb lasts so long and is it possible to replicate the outcome so as to produce light bulbs that can hold for decades and even more?

thnx!

 

It's supplied just enough voltage to incandesce, not running at anywhere near it's rated maximum. If you want to do that at home, put two bulbs of the same wattage in series or get a 220V bulb and power it from 120V. Use "rough service" bulbs; they have thicker filaments.

 

what do you mean by "rough service"?

is there a formula for the life span of a light bulb as a function of the voltage applied to it and material used as its filament?

 

There are light bulbs marketed as "rough service" for use in high vibration devices like garage door openers. They generally have a stronger more vibration resistant filament.

 

Didn't you notice that an obsolete incandescent lightbulb almost always burns out when it is turned on? When it is cold then its resistance is low then its current and power are very high. Then POOF!

But the Centennial light bulb is always turned on so it has been turned on only one time a long time ago when it was stronger.

 

I used to design products that use incandescent bulbs, herein IB, as well as drivers for them. It's been well known for a very long time that under-driving the IB results in very long lifetime, a non-linear function. Lifetime increases greatly by under-driving the IB only a moderate amount.

The problem is that of efficiency & color temperature/spectrum. At low drive level, the percentage of power converted into useful visible light is lower than that at recommended drive level. Also, the spectrum is shifted towards the red end with an under-driven IB. With an IB driven at rated voltage, deep blue is hard to see since an IB is weak in the blue/violet region. An under-driven IB makes this problem worse.

If these issues are not a problem, & the main priority is very long life, then under-drive is the way to go.

Claude

 

Didn't you notice that an obsolete incandescent lightbulb almost always burns out when it is turned on? When it is cold then its resistance is low then its current and power are very high. Then POOF!

But the Centennial light bulb is always turned on so it has been turned on only one time a long time ago when it was stronger.

so are you saying that as long as i dont turn the light off, a light bulb will keep working indefinitely?

 

No, he was not implying that if not turned off the bulb will keep working indefinitely.

However, cycling the power to an IB on and off causes it a great deal of thermal stress, shortening its' life considerably.

A typical 60W 120V lamp might have a rating of ~600 to ~1,100 hours of operation. So, if you keep the light turned on, it's average life will be somewhere in the middle of its' rating; a very few might last considerably longer or shorter than the average span - but not indefinitely.

 

I think an incandescent light bulb evaporates its tungsten filament which gets deposited onto the glass making it look black. The filament becomes thinner and weaker until it breaks.

A halogen light bulb has halogen gas inside which causes evaporated tungsten from the filament to be re-deposited back onto the filament. Then the bulb can burn hotter producing more light that is whiter.

 

I used to have a better chart but could only find this one;

You can see enormous change in life even with a 20% reduction in voltage. If you reduce the voltage further so the filament has a dull reddish glow it will last almost forever.

And it explains why my 240v bulbs last only weeks when my mains voltage is 255v. And of course turn on surge current, I measured a 100W 240v globe and it was 58 ohms cold. If that is turned on when my 255v AC mains is at a peak, then the peak filament power is 360*360/58 or 2234 watts!