Krüss spectroscope refers to gemmological spectroscopes produced by A. Krüss Optronic GmbH of Hamburg. The firm manufactures both handheld prism spectroscopes for trade and field use, and benchtop instruments mounted on integrated illumination stands for laboratory examination.

The handheld Krüss spectroscope is a compact prism instrument calibrated for the visible spectrum, typically usable from approximately 400 to 700 nanometres. It is held to the eye with the sample illuminated by a strong directional light, and the absorption pattern (chromium lines in ruby and emerald, the iron triplet of almandine garnet, the chromium-related fluorescence of red spinel, and so on) is observed against the continuous spectrum of the source. A scaled version with overlay graticule is available for approximate wavelength reading.

The benchtop instrument incorporates a halogen illuminator, a stone holder, and a fixed prism head with eyepiece, allowing prolonged examination without hand fatigue. Both instruments serve the same diagnostic purpose: rapid identification of the dominant chromophores in a stone (chromium, iron, manganese, cobalt, vanadium) and of treatments such as irradiated diamonds with the GR1 line at 741 nanometres.