Jadak Photo Research SpectraScan PR-7 Series, User Manual

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Chapter 3
– Theory of Operation
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Chapter - 3 T
HEORY OF
O
PERATION
The PR-7XX are true Spectroradiometers. They collect the optical radiation (light) through the objective lens or
other optical accessory. The signal then passes through the aperture (hole) in the aperture mirror to the
diffraction grating (see Figure 18). The grating breaks up the light into its component wavelengths much like a
prism turns white light into a rainbow. A broad band source of light such as the sun emits radiation at all
wavelengths throughout the visible spectrum. When the diffraction grating is exposed to this type of light, it will
refract the light at several angles thus creating a dispersed spectrum much like a rainbow. Similarly, if the
grating is exposed to a source such as a laser which emits a nearly monochromatic wavelength of light, only the
wavelength(s) of the laser will be refracted.
FIGURE 17
– SPECTRUM MEASURED BY THE AND PR-7XX
For the PR-730, PR-740, and PR-788, the measurement wavelength range is 380 nanometers (nm) (violet) to
780 nm (deep red)
– the visible band of the electromagnetic spectrum (see
Figure 17). For the PR-735 and PR-745, the measure band is 380 nm to 1080 nm, which includes both the
visible spectrum and part of the near infra-red spectrum.
The diffracted spectrum is then dispersed onto the detector. The detector is comprised of 512 individual
elements. Thus, each of the detector elements in both instruments samples a unique color.
During a measurement, the diffracted optical radiation (light) is sampled for a period of time determined by the
Adaptive Sensitivity™ algorithm. Adaptive Sensitivity automatically determines the correct integration (exposure)
time on the detector based on the available signal. Following the light measurement, a measurement of the dark
current of the detector is made for the same length of time that was used for the light measurement. The dark
measurement is then subtracted from the light measurement yielding the contribution of light for each detector
element.
380 nm 500 nm 600 nm 780 nm.