An accurate but simple reflectometer is described for measuring the spectral reflectances at normal incidence of flat, specularly reflecting surfaces. The instrument has a wavelength range of 0.2–2.5 µm and, with transparent samples, provides for simultaneous measurement of spectral transmittances.
J. E. SHAW and W. R. BLEVIN, "Instrument for the Absolute Measurement of Direct Spectral Reflectances at Normal Incidence," J. Opt. Soc. Am. 54, 334-336 (1964)