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Explanation
Measurement Principle
Light energy passes through the objective lens. The lights from the measurement area pass
through the hole in the center of the aperture mirror to the optical fiber, while the remaining
light is guided to the finder optics by the aperture mirror. As a result, the part equivalent to
the measurement area looks like a black circle when observed through the finder.
The light entering the optic fiber is reflected repeatedly so that it is mixed and becomes
virtually uniform. It then passes through the collimator lens to the plane diffraction grating.
After being dispersed by the grating, the light is focused by the condenser lens according
to wavelength. An array sensor is located at this focus point.
The amount of detected energy for each wavelength is then converted to a digital value by
an A/D converter, based on which the spectral radiant luminance and chromaticity are
calculated by the processing section of the CS-2000.
Sensor Section
The sensor section has a photo diode array consisting of 512 elements. The array is
always kept at constant temperature using a Peltier cooler, irrespective of the ambient
temperature. This can reduce dark current and improve S/N ratio, thus enabling
measurement of low luminance.
Dark Measurement
Each measurement consists of “light measurement” and “dark measurement”.
“Light measurement” is performed with light from the object irradiating the sensor, while
“dark measurement” is performed with no light from the object irradiating the sensor, so
that detector dark current is measured.
When measurement starts, first “light measurement” is performed. When “light measurement”
is complete, the shutter will close automatically, then “dark measurement” starts immediately.
“Dark measurement” is performed with the same integration time used for “light measurement”.
The final measured data is obtained by subtracting the measured data obtained in “dark
measurement” from the one obtained in “light measurement”. This method eliminates
influences of dark current of the array sensor, resulting in improved measurement accuracy.
Aperture mirror Collimator lens
Optical fiber
Shutter
Plane diffraction grating
Condenser lens
Array sensor
Objective lens