A light source, in particular incandescent lamp, with a bulb (1), a filament (2) arranged in the bulb (1), and a heating device (3) for the filament (2), the filament (2) emitting both visible light and heat radiation, is designed and constructed with respect to a high conversion efficiency between an electrical power input and emitted light output such that the filament (2) includes a flat section (4). A light source of this type may be produced by a method, wherein initially a filament (2) of a sintered metal powder is provided. Subsequently, the filament (2) is exposed to an atmosphere of carbon dioxide or of carbon dioxide and inert gas for forming a metal carbide. Finally, the filament (2) is sealed into the bulb (1).