Junichi Iwao


Spectrophotometers were originally designed without taking into account the fluorescent effect of papers and inks on spectrophotometric measurements. Monochromatic illumination is used in most of the available spectrophotometers, but the spectrophotometric curve measured by using monochromatic light does not approximate the same effect that is seen by the eye if fluorescence is present. White light illumination must be used to obtain a valid spectrophotometric curve of fluorescent materials. The Neugebauer equations are often used to calculate the tristimulus values of halftone prints. As long as the Neugebauer primaries do not fluoresce, measurements of primaries made by monochromatic illumination are valid. However, if the Neugebauer primaries fluoresce, these primaries have to be measured by white light illumination. If an appropriate measurement is not used to determine the tristimulus values of the Neugebauer primaries for fluorescent materials, errors are introduced in the results as calculated by these equations. The magnitude of these errors is the problem under investigation in this paper. An experimental model was established using the Neugebauer equations. The Neugebauer primaries were measured by both monochromatic and white light. Colors of 125 combinations of percent dot areas were calculated by the Neugebauer equations. The color differences in the calculations based on two modes of illumination were expressed in terms of A E, using the (U',V',W') system. AE of about 1.5 were computed for the ordinary non-fluorescent ink samples, and A E of about 12 was computed for the fluorescent ink samples. These values are based on the average color differences of the 125 colors calculated.

Library of Congress Subject Headings

Spectrophotometry; Paper--Printing properties; Printing ink--Testing

Publication Date


Document Type


Department, Program, or Center

School of Media Sciences (CIAS)


Pearson, Milton


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