Abstract: Method and apparatus for measuring the spectral transmission characteristics of gems, particularly diamonds. Polychromatic light from a light source is transmitted through a diamond to be analyzed, after which the transmitted light beam is separated into a plurality of separate wavelength bands and the intensity of light in the successive bands is measured by a first linear array of photodiodes. Simultaneously, a reference beam of light from the light source is separated into a plurality of corresponding wavelength bands, and the intensity of light in the successive bands are measured by a second linear array of photodiodes. The two measurements produced by each pair of corresponding photodiodes are then compared with each other, to provide a plurality of measurements indicative of the transmission characteristics of the diamond for the plurality of wavelength bands.