The electric bulbs are filled with chemically inactive as Nitrogen or Argon.

As when the current is passed through the bulb, the buld filament made of tungsten glow due to its high resistivity if exposed to air will cause the decomposition of tungsten metal in air which can leds

Tungsten element to melt thus causing circuit to break.

Thus for the long life of the bulb the electric bulb is filled with chemically inactive as nitrogen and argon.