[philipkglass]

Running the filaments hotter makes the bulb more efficient but also shortens the lifespan due to faster filament evaporation. You could get very long life by under-powering the bulb but then the low efficiency of incandescent lighting would go lower. That's the other remarkable thing about this paper. They use a ceramic instead of tungsten as the hot emitter, and calculate that it should have a very long lifetime.