A device which measures light wavelengths from a specimen.
Spectrometers divide light from a specimen into spectral bands. This can be accomplished with a diffraction grating, prism, filters or by using narrow band illumination. Each spectral band is then measured with a single sensor (scanning) or a row of sensors (instant). The width of each band determines the spectrometer's ability to discern spectral details. Bandwidths of 20, 10, 5, 4, 2 and 1 nm are common measuring intervals.
Some instruments measure with large bandwidths then interpolate to smaller reporting intervals, for instance the X-Rite SP-68 measures at 20 nm bandwidths (using filters) then reports at 10 nm intervals. This is called undersampling. More accurate instruments oversample the spectrum by measuring at small bandwidth intervals but report at larger bandwidths. An example of this is the Eye-One, which measures at 3.5 nm bandwidths but reports at 10 nm intervals.
Here are a few examples:
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