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Variability of spectral radiance factors of a set of fluorescent specimens was measured with eight different spectrophotometers, three designed for the two-monochromator method (2MM) using monochromatic irradiation, and five for polychromatic irradiation (1MM) using a Xenon source with a special filter technique. In four cases a single UV-filter was used that had to be adjusted to simulate the effect of D65-irradiation in the UV-range only. The inter-instrument agreement of 2MM-spectrophotometers compared to a reference instrument was within the range of the repeatability of that instrument (coverage factor k = 2). Differences of spectral radiance factors were larger for reflected radiance than for luminescent radiance, however, for colorimetric differences in most cases the opposite was true with the exception of heavily structured specimens. A certificate of a reference material containing fluorescent whitening agents was used for UV-filter adjustment in 1MM-instruments. For specimens of the same type colorimetric scatter from the reference instrument extended up to 2,4 CIELAB units, whereas in 2MM-instruments it was up to 1,5 CIELABS units only. For chromatic luminescing materials the UV-adjustment was not effective and the colour difference for 1MM readings extended up to 5,4 CIELAB units, whereas for 2MM-instruments it was up to 3,4 CIELAB units.
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