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A long time ago I had an idea for a long-lasting incandescent light bulb. You see, the reason the filament breaks is because at such high temperatures the tungsten atoms actually fly off slowly thinning the filament until its so fragile that it breaks. In addition, if one spot is slightly thinner than another, it’ll be hotter and thin more rapidly thereby creating a positive feedback loop that makes one spot get very hot and vaporize while the rest of the filament is still healthy. We can slow this process by making the filament thicker so that more tungsten has to vaporize before the bulb goes out. Now, the length and diameter of the filament are determined by the surface area and the resistance. If we want more surface area (for a higher power, higher voltage lamp) we should increase the diameter and make the filament longer to keep the resistance the same. If we want to increase the resistance (for a higher voltage but same power lamp) we can increase the length and then decrease the diameter to keep the surface area constant. So, if we want a thicker filament of the same power output, we need to decrease the length to keep the surface area (and thus power output) the same but at the cost of lower resistance. This means we need a lower driving voltage.
In order to attain this lower driving voltage, we can use an autotransformer. An autotransformer is just an inductor with a center tap (even if said tap isn’t centered but is instead closer to one end than the other). I think autotransformer actually refers to one where the location of the tap is adjustable similar to a potentiometer, but here I’m referring to one with a fixed position center tap. Anyway, it can be modeled by a transformer with two of the terminals connected to each other as shown in this circuit. It basically acts as a step-down transformer, but with one coil instead of two thereby sacrificing the isolating ability of a transformer in favor of simplicity. Since it’s a transformer, it’ll have some inductance which will harm the power factor. As you can see, a capacitor has been included to counter the inductance of the transformer thereby restoring a perfect power factor. The value of the capacitor depends on the inductance of the transformer, but I don’t know anything about what inductance values are/aren’t practical for fitting in a lightbulb so I just stuck with the default 10H. The capacitor might also be bulky and/or expensive since it’s across mains voltage. It could instead be put on the lamp side of the transformer, but at the cost of one tenth the voltage it’ll need have 100 times the capacitance, so it might just be even bulkier and more expensive.
Also, as you might have concluded already, such a lamp will no doubt cost more and possibly be bigger than normal lamps. It may also suffer other problems, such as the coil overheating the plastic casing. Furthermore, this isn’t even necessary since normal incandescent lightbulbs could last longer if planned obsolescence wasn’t a thing. In addition to that, this entire idea is terrible because who even still uses inefficient incandescent anyway? Seriously, just use LEDs. As for increasing the lifespan, just buy a bulb that doesn’t bake its LEDs with too much current. Oh, wait, such a lightbulb doesn’t exist in America, or if it does it’s illegal.
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