Incandescent lamps are the oldest forms of production of artificial light. This form of production fixture, with the advent of sound recording in the film, was the only one allowed to approach the lighting within the scene without producing the annoying hum of the carbon produced by arcing predominantly used until then. Since the advent of sound on the development of lamps and lighting was continuous and unstoppable.
The luminous efficiency of the filament is linked to the materials used to make the lamp, while the light source colour and durability are closely related to the amount of electricity and depending on the resistance of the filament. Only a maximum of 10% of the current used produces the effect radiant light, the remaining 90% will only produce thermal radiation.
With the voltage growth, the filament increases efficiency and colour temperature, but because of faster tungsten evaporation which it is composed, the overall duration of the lamp is reduced exponentially.
The tungsten evaporation deposited on the wall of glass bulb, in the case of high absorption lamp for large projectors it will produce a blackening with a lower colour temperature. This colour decay, reduced the operational life suitable for the shots. In recent years, to use the technology of incandescent bulb lamps were produced in “hard glass” that ensured smaller bulb size allowing equal dispersion of caloric radiation, the smaller projector size lighting and a longer service life.