The filament is made of tungsten wire
	Electricity flows through the filament
	The electrical resistance of the wire makes it heat up
	Tungsten resists heat very well (melting point : 3370 °C, iron: 1535°C)
	When hot, the metal of the wire emits light = Incandescence.

                   You’ve seen this before :

	When a hot plate of an electric stove  starts to glow
	The hotter the metal, the "whiter" the light that comes out. During normal operation the lamp’s filament is "white hot".