Compact Stabilized Light Sources Chapter 3: Product Overview
Page 4 CTN002682-D02
3.2. Tungsten Light Source
A tungsten light source is a form of an incandescent lamp. During operation, a
current flows through the Tungsten filament, which will heat up to around a couple
of thousand Kevin. Tungsten emits visible and infrared light at this temperature,
creating a light source that can be approximated by a black body radiator.
SLS201L is a light source known as Quartz Tungsten Halogen (QTH) light sources.
In such a light source, the Tungsten filament is sealed in a quartz envelope with
inert gas and halogen mixture filled in the bulb. Tungsten atoms evaporated from
the filament during operation will hit the gas atoms and then bounce back to the
filament, thus lowering the overall rate of filament evaporation. The halogen in the
gas mixture will also react with tungsten deposited on the inner surface of the bulb
and form tungsten halide, which evaporates more easily back to the gas mixture.
When tungsten halide gets near the filament, it dissociates at the high temperature
of the filament, creating a gradient in the concentration of tungsten. Such flow is
called the “tungsten-halogen cycle”. It effectively “pumps” the tungsten back to the
filament, prolonging the life of the light source and reducing darkening of the bulb.
SLS202L is a Tungsten filament light source for IR applications. It operates at a
lower color temperature thus generating more IR output. The filament is sealed
behind a Sapphire window which transmits IR .better than quartz. A gold reflector
is also place behind the filament which reflects the longer wavelength thus provide
higher output in the NIR to MIR range.
Figure 2 shows the structure of the tungsten bulb used in SLS201L and SLS202L
stabilized light sources. For SLS201L, the filament is sealed in a Quartz Envelope.
For SLS202L, the filament is sealed in a cavity with a sapphire protective window
on top of it. There is a gold reflector inside the cavity which reflect out all the IR
light generate from the filament.
Figure 2 Structure of the Tungsten Halogen bulb used in SLS201L/SLS202L
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