The glass bulb of incandescent lamp keeps air away from the filament to prevent it from burning up.
Most bulbs contain a mixture of gases, commonly argon and nitrogen, instead of air.
The gases help lengthen the life of the filament. Lamp manufacturers make filaments from tungsten, a strong metal that can withstand high temperatures without melting. The light from a tungsten filament is a mixture of all the colours of light found in sunlight.