In the late 50's the evolution of the lamp concept of a bulb with tungsten filament is introduced. Lamps popularly called Quartz - Iodine were born.
In a quartz bulb is placed a tungsten filament in the presence of iodine gas. This gas has proved to be suitable to create a chemical reaction that turns the tungsten, evaporated by the incandescence, produced by the current flow, into solid particles that will be deposited on the filament avoiding to blacken the bulb and allowing a more natural life and a more constant light output.
The regeneration phenomenon said "halogen cycle" needs, however, that every part of the lamp will maintain a constant temperature of 250 ° C. The quartz cruet does its part by allowing to maintain the gas high pressure introduced and preventing by its hardness, that would produce anomalous swellings at that point causing a temperature lowering that would stop the cycle. The compactness of the lamp resulting from this technology allowed to obtain luminous efficiency much higher than normal incandescent technology, constant colour temperature for a longer period of exercise and life, in proportion to the flows certainly longer. The small size of the bulbs have allowed to the projectors to reach lightness and compactness, since then impossible. The advent of the bulbs with halogen bulbs used in other evacuated glass has further improved data efficiency and durability, making today one of the most economic and accessible systems even if energy costs do not fully adapted to the times.