In 1959, General Electric patented a practical lamp using iodine.
The use of iodine was proposed in a 1933 patent, which also described the cyclic redeposition of tungsten back onto the filament. Standard and halogen incandescent bulbs are much less efficient than LED and compact fluorescent lamps, and therefore have been or are being phased out in many places.Ī carbon filament lamp using chlorine to prevent darkening of the envelope was patented in 1882, and chlorine-filled "NoVak" lamps were marketed in 1892. The small glass envelope may be enclosed in a much larger outer glass bulb, which has a lower temperature, protects the inner bulb from contamination, and makes the bulb mechanically more similar to a conventional lamp. The small size of halogen lamps permits their use in compact optical systems for projectors and illumination. This allows the filament to operate at a higher temperature than a standard incandescent lamp of similar power and operating life this also produces light with higher luminous efficacy and color temperature. The combination of the halogen gas and the tungsten filament produces a halogen-cycle chemical reaction, which redeposits evaporated tungsten on the filament, increasing its life and maintaining the clarity of the envelope. A halogen lamp (also called tungsten halogen, quartz-halogen, and quartz iodine lamp) is an incandescent lamp consisting of a tungsten filament sealed in a compact transparent envelope that is filled with a mixture of an inert gas and a small amount of a halogen, such as iodine or bromine.
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