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Video on planned obsolescence.
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james_s:

--- Quote from: SilverSolder on April 04, 2021, 05:04:39 pm ---OK but there is an unspoken assumption here -  that lowering the filament temperature is the only way to improve bulb life.  It is one way, and it is an easy way - but is it really the only way?  For example, you could make the filament thicker, so it could withstand "boiling off its surface" for longer?

--- End quote ---

You can. But what else happens when you make the filament thicker? It requires more current to reach the same temperature, so either your lamp wattage increases, or you need the supply voltage to be lower. This precisely why low voltage incandescent lamps are more efficient than high voltage lamps of the same wattage. A 240V 60W incandescent produces close to the same light output as a 120V 40W lamp. Everything is a compromise, you can gain in one area but it will cost you in another.
Miyuki:
I once saw some "special long life" incandescent with a rating of 5000h it had super thin and long fillament with a complicated support structure (230V one)
james_s:
There exist incandescent lamps rated for 50k hours, I doubt they're made anymore but they were for indicator use where long life is more important than efficiency. For most applications though, lamps are optimized for efficiency. There is another factor that affects this, an inert gas fill. The increased pressure of a gas fill reduces the evaporation rate of tungsten which allows increased life at a given filament temperature. The cost is an increase in thermal losses from convection, which becomes more pronounced with thinner filaments and this is why most line voltage lamps below about 40 watts are vacuum filled while almost all larger lamps are gas filled.
james_s:

--- Quote from: David Hess on April 04, 2021, 05:04:01 pm ---Operating life ratings for LED bulbs are disingenuous at best.  The operating life of the LEDs is 10s of thousands of hours to half brightness but failure is complete when the ballast fails, which in my experience often happens before an incandescent bulb would fail.

So how much energy is saved by using a bulb which costs more in energy to manufacturer (as measured by cost which is a good proxy), when it does not last as long?  None.  NONE!

--- End quote ---

That does not reflect my experience at all. I have numerous LED bulbs that have been in service for at least 10 years so far. Some of them I replaced due to technological obsolescence, the original ones still worked fine but the newer ones bring almost double the efficiency and better quality light. I've had a couple of early failures but even the cheapest ones have lasted longer than incandescent lamps. Even just eliminating the "flash & pop" failure mode which usually seemed to happen when I turn on a light in the middle of the night made it worthwhile to change.
SilverSolder:
So the best bet for a long life incandescent - if we lived in a cartel-free world - might be:

1) Longer, thicker filament to maintain same output while tolerating evaporation for longer (con: more complex support structure)
2) Gas fill, to suppress tungsten evaporation

and

3) Always run them on dimmers, so they only get cranked up to the max when actually needed


(point 3 is probably why I have many bulbs in this house that are >20 years old and still working!)
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