The FluoCheck tools are made possible by the capabilities of X-Rite's i1Pro 2 and i1Pro 3 spectrophotometers which supports the M0, M1, and M2 Measurement Conditions as defined in ISO 13655-2009. The FluoCheck tools were devised by BabelColor to rapidly evaluate if a color sample is susceptible to fluorescence and if two samples that match without fluorescence still match when fluorescence is taken under consideration. Here is a short description of each measurement condition: • M0: The spectral power distribution of the light incident on the measured patch should conform to CIE Illuminant A, with a color temperature of 2856 K ± 100 K. Such a light source can be found in many colorimetric instruments, such as the i1Pro and i1Pro 2. It also closely corresponds to the spectrum of many halogen desk lamps. While a 2856 K blackbody does emit UV, the UV content for M0 is often not controlled and may vary between instrument models. M0 has traditionally been used for density measurements. • M1: The spectral power distribution of the light incident on the measured patch should match CIE illuminant D50. This condition is specifically defined to study fluorescence by optical brighteners in the paper and /or in the printing inks. According to ISO 13655, conformance to M1 can be achieved by two methods. The first method is by providing a source which exactly matches illuminant D50 in both the UV and visible regions of the spectrum, with the UV requirement more precisely defined by ISO 3664. The second method is providing a separate UV source which replicates the effect of UV light on the optical brighteners of the paper; this is the method used in the i1Pro 2 (and apparently also by the i1Pro 3). • M2: The measurement shall contain no contribution from optical brightening agents in the paper. While the spectral distribution is not explicitly defined, it shall be continuous in the wavelength range from 420 nm to at least 700 nm. The standard does not specify if the source should be filtered or if the measurement can be deduced from measurements with and without UV content. The i1Pro 2 uses the second method; it does not have a physical UV filter, and M2 data is obtained by processing the M0 and UV light measurements. If a paper is not fluorescent, then M0, M1 and M2 should be equal. The FluoCheck tools enable you to: characterize the Fluorescence Index (FI) of a single printed sample by computing the color difference between a measurement done under the M2 (UV-cut) measurement condition, and either M0 (Illuminant A) or M1 (D50); evaluate if the combined appearance of two printed samples varies between a reference Measurement Condition (M2, UV- cut) and a UV-inducing illuminant (either M0 or M1) using a Fluorescence Metamerism Index (FMI); judge how samples look under the M0, M1, and M2 measurement conditions and, for M2 (UV-cut), judge how they look under Illuminant A and D50 (virtual light box). In the screenshot below we show measurements made directly on two papers. The first paper, measured on the Reference side on the left, is from a glossy magazine. The second paper, measured on the Sample side on the right, is a paper used for paint chips. While the fluorescence is quite high in both cases, the fluorescent agents were used for quite different purposes.

For the magazine paper, the M2 (UV-cut) measurement at D50 shows that the base paper is quite neutral to start with (L*a*b*: 93,82 / 0,52 / 0,81) and the M1 (D50) measurement is visibly bluish, making the paper look whiter than white. For the paint chip paper, the M2 (UV- cut) measurement at D50 is yellowish while the M1 measurement is very neutral (93,64 / -0,06 / -0,01), so that the paint chip color may be evaluated with more accuracy. The color-differences between the patch colors obtained with the UV-cut (M2) measurement condition and the colors obtained with the M1 measurement conditions are the Fluorescent Indices (the measurements between M2 and M0 provide additional FIs). In this example the FI is computed using the CIEDE2000 color-difference formula; the FI computed between M1 and M2, relative to the the D50 illuminant, is 4,46 for the magazine paper and 4,19 for the paint chip paper. These color differences are very similar even if in one case the fluorescence is used to enhance perceived whiteness, and in the other case fluorescence is used to achieve a neutral color (the patch in the middle of the left side is very close to the patch at the bottom of the right side). Both papers also exhibit fluorescence relative to M0 (Illuminant A), but in a lesser degree, as expected because of the lower UV content of this Illuminant when compared to D50. Here again the FI values are quite similar, with 2,72 for the magazine paper and 2,49 for the paint chip paper. Now, if we consider both samples together, we see that they change in a similar manner between M1 and M2 and between M0 and M2, even if there not similar in any given measurement condition. This commonness in change is reflected in the FMI values which are very low, either for M0 relative to M2, labeled FMI(M0), or for M1 relative to M2, labeled FMI(M1). Please consult the FluoCheck section of the CT&A Help manual for additional examples.