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Why do inorganic LED bulbs have a limited lifespan? For example, a manufacturer may quote that a bulb or monitor powered by an organic light emitting diode(s) has a lifespan of 50,000 hours, while it may quote the lifespan of that powered by the inorganic LED(s) to be 70,000 hours.

For OLEDs, it is understandable why they wear out. That is because in chemistry, I learned that polymers are made up of hugely complex, varying molecules that are not inert and are only weakly held between each other by weak van der Waals forces. If a bond breaks within a molecule for example, the original molecule will almost certainly not reform. That is because there are so many possible different atoms to form new bonds with, so the original bond will almost certainly not be reinstated due to probability. Because they are unstable, they self-react, which causes them to self-destruct over time. That is greatly accelerated by external high-energy sources such as ultraviolet rays. Since OLEDs are made out of polymers, that is why they break down over time.

However, inorganic LEDs are made out of glass or ceramic. In chemistry, I learned that glasses and ceramics have a very simple chemical composition with their structure tightly held together by strong atomic bonds. Glasses and ceramics are distinguished between each other because the former has a disordered structure, known as amorphous, while the latter has an ordered structure, known as crystalline. Because of how highly stable they are, they do not change at all under there is an super high-energy event from an external source that causes the bond to break, such as a macroscopic force cracking the material, high temperatures melting the material, or super corrosive chemicals. Similarly, a few days ago, I did an Internet search confirming my suspicions that solid-state ceramic and glass capacitors last forever under normal operation because they do not age at all within design limits.

So, shouldn't inorganic LEDs last forever (geological timescales) when its design parameters are never exceeded under operation, such as never having a power surge? Electrical conductivity is a property of electronic components (of which diode is a specific type, more specifically LED), just like visible light conductivity is a property of glass. Passing light through glass never wears out glass given that it does not overheat, so shouldn't passing electric current of the correct polarity through an inorganic LED never wear out the LED given that it never overheats?

Are the lifespans of inorganic LED bulbs just limited by the driver (required because the LEDs themselves only work with DC in one direction), which presumably typically contains an electrolytic capacitor? Under the absense of freak events, do they fail just because the electrolytic capacitor fails or the solder in the driver oxidizes? If the driver were only made out of materials that are corrosion-proof under normal atmospheric conposition and only contained ceramic/glass capacitors, would that mean the inorganic LED bulb would last geological timescales?

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This is not a rigorous answer, but even a piece of steel will change if you just let it sit there for long enough. And I'm not talking about rust; I'm talking about the additives dissolved in the steel. Depending on what you need the piece of steel to do, it might very well be good enough to use even after sitting there for geological time scales. However, sometimes even these changes are too much and the steel needs to be stabilized.

Then consider that semiconductors make use of very finely tuned material compositions. The dopants and additives in there are able to slowly diffuse out. It's not completely stable.

Similarly, if your glass or ceramic plate capacitors don't need to rely on such finely tuned material composition to perform satisfactorily, you can probably tolerate a lot more changes due to the aging of the material. But for a semiconductor that relies on a much more specific material composition, you obviously will tolerate a lot less.

I don't think the material requirements for glass or ceramic plate capacitors is fair comparison to semiconductors. Perhaps more fair would be to look at the aging effects of optical coloured glass filters, though I have no knowledge about their aging effects. However, they are composed of glass with additives and are required to have properties that can deviate much less than capacitors.

Oh, and as for glass being stable. Perhaps you should know that coloured glass filters for optics, particularly UV-pass filters can actually oxidize due to humidity in the air. Furthermore, they actually degrade in the presence of sufficiently strong UV light. So although regular glass may be stable on geological time scales you cannot extend that to glass with additives. Not all glass is the same.

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  • $\begingroup$ Wow! I never knew that. I always thought a piece of steel (given that it does not contain any radioactive isotope) lasts forever if it does not have macroscopic physical damage, corrosion, or fatigue. I thought those were the only ways to degrade steel. Ditto with the glass optical filters. $\endgroup$ Sep 18 at 1:42
  • $\begingroup$ @CoastCityLapse00crashtest Well, consider that the platinum-iridium alloy bar that was made to represent the kg. Obviously it was specifically made to be as stable as possible. And it didn't even need to be dimensionally stable. It just needed to stay the same mass. It was found to have changed in mass (gained mass of all things) and apparently they don't know why (at least last I heard). $\endgroup$
    – DKNguyen
    Sep 18 at 1:45
  • $\begingroup$ I thought the mass change of the IPK was able to be described by offgassing because the metallurgical technology back then wasn't good enough to make a single crystal of platinum-iridium like they are able to produce a single boule for electronic components nowadays. Am I missing anything? $\endgroup$ Sep 18 at 5:09
  • $\begingroup$ I don't know anything about that. $\endgroup$
    – DKNguyen
    Sep 18 at 5:10

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