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FLEXO Magazine : May 2012
graphic arts industry. The ISO 13655 standard stipulates that the lamp should conform to a correlated color temperature of 2,856° Kelvin plus or minus 100° Kelvin. Again, this is a common requirement for widespread measurement prac- tices today. Because the strength of ultraviolet light that a lamp can emit is not specified in M0, it is not the recommended way to measure projects printed with inks or substrates that fluoresce significantly. Most specifications such as FOGRA, FIRST, IDEAlliance as well as the current ISO 12647 series are based on M0 data. ILLUMINATION CONDITION M1 Companies should use measurement condition M1 to reduce variations between instruments due to fluorescence, either by optical brighteners in paper or fluorescence of the imaging colorants or proofing colorants. The ISO committee recom- mended the use of spectro- photometers with lamps that closely match the CIE Illumi- nant D50 as the recommended method for measurement con- dition M1 for both substrates and inks that fluoresce. But, again, the committee recognized that the vast major- ity of hand-held spectropho- tometers have lamps that do not closely match D50 and ac- complishing this in a hand-held instrument would be difficult. To try to provide some workable methods until such instruments are readily available, the com- mittee said companies could use a limited definition of M1 that is valid for measuring opti- cally brightened papers only, but not for measuring inks or toners that fluoresce. The second definition said that a company could use a lamp that doesn’t exactly match D50 in the range of wavelengths of 400 nm to 700 nm, as long as the company uses a controlled adjustment of wavelengths below 400 nm. The standard also stipulates that the ratio of the power of wavelengths in the 300 nm to 400 nm range to the 400 nm to 500 nm in the lamp closely match that same ratio in D50. M1 is the only choice when a company needs accurate colo- rimetric data and the project uses printing inks that fluoresce. The ISO committee recognized that many companies do not have hand-held spectrophotometers that can reliably measure fluorescence with D50. According to the committee, the best way around this is for process control and data exchange applications between companies to use the same make and model of spectrophotometers with good historical agreement. ILLUMINATION CONDITION M2 The ISO committee said that measurement condition M2 should be used by companies when measuring projects that are printed on substrates that fluoresce and want to obtain data by excluding the substrate fluorescence. 54 FLEXO may 2012 www.flexography.org