Halogen
Lamps
Halogen Lamps
Laser Light Measurement Systems
LCD / DLP TV Lamps
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Halogen Lamps
Halogen Lamps are similar in construction to conventional gas
filled
tungsten filament lamps except for a small trace of halogen (normally
bromine) in the fill gas. The halogen gas reacts with the tungsten that
has evaporated, migrated outward, and been deposited on the lamp wall.
As the quartz envelope wall reaches a temperature of approximately
250C, the halogen reacts with the tungsten to form tungsten
halide, which is freed from the wall of the lamp and migrates back to
the filament. The halide compound reacts at the filament where
temperatures approximating 2,500C cause the tungsten and
halogen to dissociate. The tungsten deposits onto the colder portions
of the filament, and the halogen is freed to continue the cycle.
The filament of a Halogen Lamp has two purposes. One is to
generate
light, and the second is to generate the heat necessary to obtain a
wall temperature exceeding 250C. These lamps have been
designed to maintain this required wall temperature when operated at
design voltage. A reduction of voltage exceeding 10% from the design
voltage will probably result in the wall temperature falling below the
required 250C. Tests reveal that in most cases this reduced
operating condition is not detrimental to the operation of the lamp. By
the time the wall temperature drops to a point where the halogen cycle
ceases to function, the filament temperature has diminished to a point
where the tungsten evaporation is negligible. If wall blackening is
noticed, the operating voltage range at which this occurs should be
avoided. Burning the lamp at design voltage for a short period of time
can usually clean up lamp blackening due to temporary operation in such
a voltage range. However, on rare occasions halogen lamps de- rated by
more than 10% could experience an adverse reaction of the corrosive
halogen attacking the tungsten filament causing premature lamp failure.
Operating Halogen Lamps at voltages exceeding design voltage is not
recommended as the lamps are normally designed to their maximum limits.
Lamp seal temperatures must not exceed 350C or oxidation of
the molybdenum ribbon will occur resulting in premature lamp failure.
Halogen Lamps are ideal light sources for spectrophotometers as they provide broad band spectral radiation ranging from the ultraviolet, through the visible and into the infrared out to five microns. Some radiation output can be obtained at 320 and 340 nanometers.
