In general, incandescent light comes from the heating of a metal (tungsten) filament in the absence of oxygen to prevent the metal from burning up. When the metal atoms are excited, electrons go to higher orbitals, and when they return to their native orbitals they give off light and heat. What goes on in a light bulb is the same thing that goes on when iron is heated to orange and then white. Tungsten is used because it produces some of the brightest light with an affordable filament.