Electric current passes through a filament of an incandescent bulb, thereby increasing it temperature. When current flows, it contains electrons through the filament to produce light. Typically, incandescent light bulb consists of a glass enclosure that contains tungsten filament. The glass enclosure contains either a vacuum or an inert gas that serves as the filament protection from evaporating. Incandescent light bulbs contain a stem attached at to its base to allow the electrical contacts to run through the envelope without gas or air leaks.