16-02-2013, 11:54 AM
HALOGEN LAMP
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HISTORY OF HALOGEN LAMP
A carbon filament lamp using halogen to prevent darkening of the envelope was patented in 1882 .
The chlorine-filled "Novak" lamps were marketed in 1892
The use of iodine was proposed in 1933
Elmer Fridrich and Emmet Wiley developed the halogen lamp at General Electric in Nela Park, Ohio in 1955
Elmer Fridrich developed the first halogen tungsten lamp prototypes with Emmitt Wiley in 1953/1959 .
The team later developed the double ended halogen lamp in 1959
Patents were issued in 1959 .
The halogen was improved upon by other engineers so that it was cheaper to produce and market in 1960.
Definition of Halogen Lamp
A halogen lamp, also known as a tungsten halogen lamp or quartz iodine lamp, is an incandescent lamp that has a small amount of a halogen such as iodine or bromine added
The combination of the halogen gas and the tungsten filament produces a halogen cycle chemical reaction which redeposit evaporated tungsten back on the filament, increasing its life and maintaining the clarity of the envelope.
Because of this, a halogen lamp can be operated at a higher temperature than a standard gas-filled lamp of similar power and operating life, producing light of a higher luminous efficacy and color temperature
CONSTRUCTION OF HALOGEN LAMP
Contact - Metal part that establishes electric contact between the base of a light bulb and the socket
Base - Metal end of a light bulb inserted into a socket to connect it to the electric circuit
Inert gas - Gas inserted in the bulb to slow down evaporation of the filament; iodine or bromine are added as they combine with the tungsten at high temperatures.
Tungsten filament - Very thin metal wire emitting light rays when an electric current passes though it.
OPERATING PRINCIPLE
If the lamp is turned on , tungsten particles evaporate from filament and attach on the bulb wall . At the same time ,halogen is decomposed and becomes atomic halogen .
Atomic halogen is diffused on the bulb wall with free tungsten particle to become transparent and volatile tungsten halide .
Due to the high temperature ( over 500 degree Fahrenheit) on the wall , tungsten halide is volatilized and circulates back to filament
Effect of voltage on performance of Halogen Lamp
Tungsten halogen lamps behave in a similar manner to other incandescent lamps when run on a different voltage.
Light output is reported as proportional to V3
The luminous efficacy proportional to voltage V1.3
Lifetime is that it is proportional to V-14
Increasing the applied voltage increases the rate of evaporation .
With a reduced voltage the evaporation is lower .
Halogen lamps are dimmed successfully .