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1. Halogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style (formerly: VII, VIIA) of the periodic table, comprising fluorine, (F); chlorine, (Cl); bromine, (Br); iodine, (I); and astatine, (At). The undiscovered element 117, temporarily named ununseptium, may also be a halogen.
The group of halogens is the only periodic table group which contains elements in all three familiar states of matter at standard temperature and pressure.
2. Halogen
A halogen lamp is an incandescent lamp in which a tungsten filament is sealed into a compact transparent envelope filled with an inert gas and a small amount of halogen such as iodine or bromine. The reason that incandescent lamps burn out is evaporation of the filament, tungsten in this case. The tungsten filament inside of a bulb can heat up to thousands of degrees. The combination of the halogen gas and the tungsten filament produces a chemical reaction known as a halogen cycle that increases the lifetime of the bulb and prevents its darkening by redepositing tungsten from the inside of the bulb back onto the filament. The halogen lamp can operate its filament at a higher temperature than a standard gas filled lamp of similar power without loss of operating life. This gives it a higher efficacy (10-30 lm/W). It also gives light of a higher color temperature compared to a non-halogen incandescent lamp. Alternatively, it may be designed to have perhaps twice the life with the same or slightly higher efficacy. Because of their smaller size, halogen lamps can advantageously be used with optical systems that are more efficient. |
