The interference filter is very common in instruments,
especially those produced during the early rise of
industrial color matching in the 1970’s and 80’s.
The interference filter is mounted as a filter wheel which is
usually rotated by a small electric motor directly in line
with the sample and/or reference beam. This simple
design uses a single photodiode detector which measures
the dispersed light as the filter rotates resulting in bands
of variable width. Most are designed to provide an
average rather than a fixed bandwidth of about 10nm.
Many instruments still in use today are based upon this
interference filter such as the Hunter D53, D54, and the
ACS Spectro-Sensor, and the ACS Chroma-Sensor 5.
Interference filters may also be positioned statically in
sequence to provide the necessary spectral distribution.
The resulting bands are measured with diode array
detectors situated accordingly and are usually 12-15 nm
in bandwidth. Instruments of this type are the X-rite
portable spectrophotometers such as 968, and SP series.