Looked up old notes.
Some types of filaments are prone to vibrate due to the changing magnetic field created by the AC current flowing through them. Coiled coil being often the most affected. Striaght wire filaments are not significantly affected.
On "pure" un-dimmed mains this magnetic field and hence the vibration is a smooth sine wave with no sharp edges. On dimmed mains the sine wave is chopped and there are sharp changes to the magnetic field and "jerks" in the vibration. This can shorten the life of the filament by mechanical wear.
However it doesn't explain the rapid failure.
Some types of filaments are prone to vibrate due to the changing magnetic field created by the AC current flowing through them. Coiled coil being often the most affected. Striaght wire filaments are not significantly affected.
On "pure" un-dimmed mains this magnetic field and hence the vibration is a smooth sine wave with no sharp edges. On dimmed mains the sine wave is chopped and there are sharp changes to the magnetic field and "jerks" in the vibration. This can shorten the life of the filament by mechanical wear.
However it doesn't explain the rapid failure.
