The incandescent light bulb produces light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from oxidation in the air with a glass enclosure that is filled with inert gas or evacuated. In a halogen lamp, filament evaporation is prevented by a chemical process that redeposits metal vapour onto the filament, extending its life. The light bulb is supplied with electrical current by feed-through terminals or wires embedded in the glass.