How did the mercury pump help make practical incandescent lamps possible?

The mercury pump was essential to the development of the practical incandescent lamp because it provided the means to create an adequate vacuum within the glass bulb.1

Early attempts at incandescent lighting often failed because the filament would oxidize and burn away rapidly when exposed to air. By using a mercury pump—invented in 1865—to evacuate the air from the bulb, inventors like Sir Joseph Wilson Swan and Thomas Alva Edison were able to protect the carbon filament from oxidation. This vacuum allowed the filament to glow steadily for extended periods, transforming the incandescent lamp from a short-lived experimental device into a viable, practical lighting system.21