enhances machine vision
Light source selection: one key to a successful short-wave infrared
Martin H. Ettenberg, James Gardiner, and Mark Kolvites
Most machine vision and image processing
system developers have deployed cameras sensitive in the visible band for quality control, process control, or in applications requiring the differentiation of objects. Traditional visible-band
methods include broadband white light, which
allows the camera to see all the visible colors. Or
to more effectively observe certain colors, developers may choose light of specific wavelength(s)
such as red, blue or green.
For such visible-band applications, developers of illumination systems for use in the
machine vision and image processing market
have done an excellent job producing a wide
variety of commercial-of-the-shelf lighting
options in various form factors and colors.
However, as developers turn to non-visible
band imaging methods, illumination can
become a more challenging proposition.
Imaging beyond the visible
One such non-visible spectral band is the
short-wave infrared (SWIR) band (defined
here as 750-2600nm). Many materials that
appear similar in the visible spectrum, look
very different in SWIR. Figure 1 shows 4 different liquids (water, acetone, TCE, and isopropyl alcohol). All appear clear in the visible,
but very different when imaged with broadband light in the SWIR.
In the visible band, today’s silicon cameras
enable imaging from approximately 400nm to
1050nm, just beyond the visible and into the
near infrared (NIR) band with readily available light sources at wavelengths of 850 and
950nm. However, seeing beyond this range
with reflected light requires another detector
material such as Indium Gallium Arsenide
(InGaAs), Mercury Cadmium Telluride or
Indium Antimonide camera.
Since reflective properties of different atomic
structures vary in the SWIR band, an uncooled
InGaAs camera provides a simple way to image
from 400nm to 1700nm enabling easy differen-
tiation of many materials that often look similar
in the visible band.
Figure 2 shows multiple epoxies that look
either clear, dark, light or are similar in color
to the substrate in the visible band. The various
epoxies and caulks use different materials with
fillers whose colors almost match in the visible.
Figure 1. Four liquids (water, acetone, TCE,
and isopropyl alcohol) that appear clear and
transparent in the visible (top) are very differ-
ent when imaged in the SWIR band (bottom).
Martin H. Ettenberg, Ph.D., from
Princeton Infrared Technologies (
Monmouth Junction, NJ, USA; www.princetonirtech.com); James Gardiner,
Mark Kolvites from Metaphase Technologies, Inc. (Bristol, PA, USA; www.