Turbidimeters and nephelometers measure the scattering of light through a liquid sample, which is a physical analysis function using optical radiation. They generally classify under heading 9027.50 rather than 9027.30, because they do not disperse radiation into a spectrum. The specific 10-digit line depends on whether the instrument is electrical and whether its primary function is characterized as physical or chemical analysis.

Multi-mode plate readers that perform absorbance, fluorescence, and luminescence measurements using optical radiation typically classify under heading 9027.50 as electrical instruments for physical or chemical analysis using optical radiations. Supporting documentation should include the manufacturer's technical specification sheet confirming the optical detection modes, the intended analytical application, and the absence of a spectral-dispersion element (which would point toward 9027.30 instead).