Why are incandescent lamps with tungsten filaments filled with an inert gas such as argon?

When the light is turned on, the tungsten filament heats up to a white temperature. Argon, an inert gas, shields the filament from ionization by resisting the flow of current through it. An engineer at a lamp factory once responded to a question I asked about light bulbs: ideally, there should be no gas inside the bulb for ionization. Unfortunately, it is simpler to fill a lightbulb with an excess of inert gas than to remove it and seal it.

When operating an inert gas glove box, it is frequently possible to drill a hole in a regular light bulb (which is a difficult task), insert it into the box, and turn on the power source while the light bulb is still shining and the environment is suitable.

In order to keep the tungsten filament from oxidizing at high temperatures and to preserve the lamp's efficiency, incandescent lamps with tungsten filaments are filled with an inert gas, such as argon.