Why is it that light bulbs never seem to fail during operation? Instead, they almost always expire after being turned on one too many times.
It's probably happened to all of us; we hit the switch on the wall and a light turns on only to immediately burn out due to a broken filament.
This annoyance is made very rare by energy efficient long lasting light bulbs, but for now let's stick to the failure of incandescents.
The end of life events of incandescents are easily explainable.
The incandescent's source of light, the tungsten filament, gets viciously hot while adequate voltage for illumination is flowing through out.
The intense heat constantly and consistently degrades the filament, causing oxidation and rusting.
Eventually the filament sustains too much damage and the next time the light switch is flipped, the lamp may briefly start but soon burns out.
It simply can't handle the voltage overload sent each time the electricity is switched on.
Incandescent light bulbs are basically on the road to failure from the first time they are switched on.
Eventually the startup voltage overload becomes too much for the weakened filament and it breaks.
That's one way an incandescent light bulb can fail; another is due to an uneven filament.
Certain points along the tungsten coil evaporate and thin out the filament during operation.
This can also cause coils of the filament to get pushed together.
Heat builds up significantly faster in the thin areas of a filament, or where coils are pressed together.
This extra heat becomes too much and the filament breaks or even melts.
It's the initial stress on the tungsten filament that leads to an incandescent light bulb's eventual failure.
They seem to work best when operating 100% of the time, with no mind to the stresses and strains of overloaded voltage at startup.