Solution

An inert gas does not chemically react with the material of the heated filament and does not destroy it. A low-density gas has low thermal conductivity, which increases the efficiency of the electric lightbulb as a lighting device by reducing the thermal power dissipated into the environment.

In addition, due to its nearly spherical shape, the structural strength of the glass bulb against internal bursting is significantly lower than its compressive strength against external pressure. Therefore, it is advisable to fill the lamp with gas at such an initial pressure that, when heated to operating temperatures, its pressure does not exceed atmospheric pressure.