The increased use of optical brightening agents (OBAs) in substrates for printing is well documented, as are the complications surrounding spectrophotometric color measurement when OBAs are present. In an effort to better address measurement of OBAs, the International Standards Organization (ISO) has published ISO 13566:2009, where the illuminations utilized in spectrophotometric instrumentation is more clearly defined than in previous standards. It is recognized that moving ahead the illuminant utilized in spectrophotometers should be able to better correlate to standardized viewing conditions, including the amount of ultra-violet (UV) present in the illuminant, as the effect of the OBAs is dependent on the amount of UV.
Of particular note, ISO 13655:2009 recognizes measurement condition M0 as a 'legacy' condition, representative of the wide range of spectrophotometers utilized in the field. Condition M0 instruments illuminants correspond to illuminant "A," while measurement condition "M1" specifies that that the instrument illumination corresponds to D50, which is better correlated to standardized viewing conditions and has a more clearly defined UV component. One goal of M1 is to achieve better agreement between various manufacturers and models of instrumentation.
While M1 instruments are being utilized more and more frequently in the field, there is a large population of legacy M0 instruments also in use. For those interested in understanding the variation that can be expected in the comparison of various instruments, the question of how much variation can be eliminated through the exclusive adoption of M1 instruments is especially germane.