What effect does operating an incandescent bulb at lower voltage have on its lifespan?

Operating an incandescent bulb at lower voltage does indeed prolong its lifespan. This phenomenon occurs because incandescent bulbs produce light through the heating of a filament. When the voltage is reduced, the current passing through the filament also decreases, leading to less heat being generated.

At lower temperatures, the filament experiences less thermal stress which reduces the rate of evaporation of the tungsten in the filament. Since the evaporation of tungsten is what primarily leads to the filament's thinning and eventual failure, operating at a lower voltage means that the filament will last longer before it breaks.

Moreover, operating at a lower voltage typically results in a dimmer light output; however, the significant benefit is the increased durability of the bulb, allowing it to be used for a longer period before needing replacement. This is an important consideration for efficiency and maintenance in both residential and commercial applications.