FREQUENTLY ASKED
QUESTIONS
What is an incandescent light source?
Incandescent light sources are electric bulbs with filaments.
When electric energy is transformed into heat energy the temperature
of the solid bodies are raised. The heated body gives off different
levels of light according to the degree to which it has been
heated. Halogen bulbs fall under this category.
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What materials are used in halogen lamps?
There are two kinds of bulbs used in halogen lamps: transparent
and translucent quartz bulbs. Materials inside the halogen lamp
include tungsten filament, molybdenum foil, and filling gases
consisting of a combination of Nitrogen (N2), Argon (AR), Krypton
(Kr) and a small amount of halogen gas made up of iodine (I),
bromine (Br), chlorine (Cl), and fluorine (F). The base of the
lamp is usually made of steatite or heat-resistant metal.
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Why is the halogen bulb made of quartz?
Quartz is used in halogen bulbs because it can withstand high
temperatures. Quartz also ensures against heat shock.
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Why is tungsten used as the filament?
Tungsten is used because of its high flexibility and low rate
of evaporation at high temperatures. Tungsten also has a very
high melting point of 3400°C. This lends to its slow evaporation.
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Why is molybdenum foil used inside the
halogen lamp?
Molybdenum foils is used as a conductor through the seal part
of lamp. It insures the hermetic sealing of the lamp. Molybdenum
has almost the same thermal expansion properties as quartz.
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How does a halogen lamp work?
It works through the halogen cycle. As tungsten evaporates from
the filament, it combines with halogen gas and becomes tungsten
halide. This tungsten halide state is maintained at temperatures
between 250°C and 1400°C. The temperature of the bulb is kept
above 250°C in order to maintain this state and prevent the
tungsten from sticking to the bulb wall and darkening it. When
the tungsten halide nears the filament, the heat of the filament
separates the tungsten from the halogen gas, redepositing the
tungsten on the filament. The freed halogen gas then repeats
the same process again thus the halogen cycle.
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How do halogen lamps give constant light
output?
The halogen cycle effectively prevents blackening of the bulb
wall so that there is no reduction of light output or color
temperature.
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How does a halogen bulb give a longer
lamp-life?
Halogen bulbs are more efficient than ordinary incandescent
bulbs. They can give a longer lamp life expectancy because of
the halogen cycle.
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What is color temperature?
Color temperature is the temperature at which a black body emits
radiant energy competent to evoke a color of the same hue and
saturation as that evoked by radiant energy from a given source.
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Why does a light bulb burn out?
Due to the high temperature the tungsten filament is operated
at, some of the tungsten evaporates during use. This evaporation
leaves the filament thinner on some areas. The weakened area
of the filament becomes hotter, which leads to even faster evaporation
causing the filament to burn back and the lamp to burn out.
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Why do some bulbs burn out the instant
they are turned on?
The thinned filament in a cold state can not withstand the inrush
surge of energy and thus the bulb burns out.
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Why does a bubble sometimes form on the
quartz wall of the halogen bulb?
This is due to the quartz halogen lamp being overheated. This
causes the filament inside the bulb to sag and become too close
to the quartz envelope thus creating a bubble.
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What are the common causes of lamp failure?
The most common causes are over heating and over voltage.
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How can you prevent over heating?
Never operate the halogen lamp above the rated operating temperature.
The seal temperature should always be maintained below 350°C
and the bulb temperature should be kept between 250°C and 550°C.
Make sure the cooling system is functioning properly. Do not
allow one lamp to directly expose another. If a reflector is
being used make certain the IR is not reflected back onto the
filament or its support. Finally, make certain particles do
not fall on the lamp.
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How can you prevent over voltage?
The lamp should never operate beyond 8% of the total rated voltage.
Check that the power supply or line voltage is not delivering
spikes or surges to the lamp. It may be necessary to place in-line
suppressors in your system. Inspect your sockets periodically.
Bad connections will cause arcing which may surge the lamp.
Avoid the use of dimmers that may drive your lamp over the rated
voltage. Finally, avoid any unnecessary vibrations.
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What to do if you have a problem with
an USHIO lamp?
In the event that you experience a problem using an USHIO lamp,
please return it to your local USHIO distributor. Please include
a description of the problem and the lamp’s hours of operation.
From that point, it will be determined if the problem resulted
from a user error or a production error. In any event, constructive
advice will be given to you on how to avoid the situation in
the future.
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