Just to brighten up a winter's Monday morning (for those of us in the Northern hemisphere), another thread on these forums has just reminded me of this light bulb which has been lit for 117 years...there's even a live webcam so that you can check it's still alight
But to be honest, it is not really a light bulb. It is only glowing slightly. It must be run under its rated Voltage, this will prolong the life of any tungsten filament lamp. It is more like a low Wattage heater. You probably could not read a newspaper in the dark if you were just a foot away from it.
And, of course, also one of the critical things is that it hasn't been turned on and off very often - there will be others in the IET who know much more about this than I do, but I seem to remember that thermal shock is usually the trigger for failures of incandescent lights. I'm guess when they have turned it off and on in recent years they've done it very gently!
That is very interesting. I have an L.E.D. lamp that has been in use continually 24/7 for over a year. Let's see how it compares. I seem to recall regarding tungsten filament lamps that an over Voltage of ten percent can halve the lamp life, if memory serves me correctly.
Not bad for a hand-blown, carbon-filament light bulb running on 120VAC. It was manufactured by the Shelby Electric Company in Shelby, OH. You can still buy working examples on eBay!
I've mentioned this before somewhere, Thomas Edison's summer residence has a carbon lamp that has been continually running for about 60 odd years.
AFAIK.. LED indicator lamps have a MTBF of around 100k. Hrs. But then turning up the 'volume' reduces life expectancy to, as advertised, as 30k.hrs then 25k hrs and now anywhere between 10 and 3k hrs.
Some years ago I was sent to a property in the heart of rural Cumbria, to disconnect the incoming mains for a private electrician who'd been called in to check the wiring. The place had been wired decades ago by the customer's father, and apart from a couple of new spurs here and there had never been touched since. The customer pointed proudly at a bulb hanging from what resembled a bit of frayed string hanging from the kitchen ceiling, and told me his father had purchased that bulb during the war and it was "still going strong". The bulb was indeed still working - just - but "going strong" was stretching things somewhat - it contained a big loop of filament, glowing a dull orange like a toaster element. Definitely a museum piece!
Photographic tungsten lamps used the inverse principle. Increase the voltage (or effect - lamp's filament resistance) by 10%, increases the lumen output and hence light temperature but reduces the lamp's life to about 10% (100 hours reduces to 10 hours). Heat (something to do with the poor thermal cycle of tungsten in the envelope) and thermal shock being contributing factors.
