Soft-starting a filament lamp will extend it's life hugely, eg switching on with a dimmer.
The peak voltage of a 240Vac supply is around 350v volts, if you switching with a normal mechanical switch you have no control of the voltage supplied to the load at the instant you switch 'on' - it could be 350v, equally it could be 0v. Shoving 350v across a bit of wire is going to give it one hell of a kick (albeit for a v short time), at least if you switch on at the 0v instant (zero crossing switching) the lamp filament has chance to warm up for .01 sec.
I had a customer who had problems with filament lamps failing due to the high frequency at which the were switched on and off. I improved matters enormously by not switching the lamps off fully. We applied a low voltage to the bulb, not enough to illuminate it but enough to keep the filament hot. When the lamp was switched on fully it wasn't so much of a shock = longer life.