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Why does an electric light bulb nearly always burn out just as you turn on the light, almost never while the light is shining?

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An electric light bulb is not an ideal resistor.  This means that as the filament in the light bulb heats up, its resistance changes.  When it is cool, the resistance is the...

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The effect is much worse if your bulb is being dimmed by a cheap dimmer switch, because even though the filament is getting less power, it's getting it in a very choppy form that often causes the filament to oscillate and buzz. Better dimmers have a choke and some capacitors to help smooth out the choppy signal coming from the triac.