Why do light bulbs burn out when turned on, but not while shining?

[9danny]

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

 

[chroot]

The filament is rapidly becoming hotter, and thus rapidly undergoing thermal expansion. During this expansion, any small imperfection may cause it to break.

Once the bulb is in steady-state, the filament no longer grows hotter, and no longer expands.

- Warren

 

[turbo]

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.