Danny C. Rich

Improved model for improving the inter-instrument agreement of spectrocolorimeters

Abstract A proposal by Robertson slightly modified by Berns and Petersen, to use spectral differences to predict systematic errors in spectrophotometers has found limited success in practical application. Porter suggested a way to improve the level of agreement between standardizing laboratories based on the Berns and Petersen method but suggested using derivatives calculated from piecewise polynomial splines. He did not know it at the time, but such a model was already in use. That model now has over five years of successful field testing and this paper discloses how the model was developed, the efficiency with which it can reduce systematic errors and the kinds of errors that cannot presently be corrected by computational comparison of reflectance or transmittance factor readings. For instruments of the same basic design, this model will produce a reduction of the systematic errors in colorimetric coordinates on the order of factors of 2–3. The magnitude of the initial color differences appears to be irrelevant. The corrective power of the model is limited by the numerical noise generated by the process of simulating analytical derivatives. We show that instruments with average color differences of 1.0 CIELAB unit can be reduced to a level of 0.5–0.3 units. Our testing has included a large variety of material samples including textiles, plastics, inks, paints and ceramics. Over 400 samples have been measured in proving this method. In addition, the model has been in place in industrial environments where multiple instruments of different manufacturer have been made to operate successfully from the same set of laboratory standards at reproducibility levels that rival those of national standards laboratories.

A review of solid-state lighting and its impact on the marketing and production of decorative coatings

Solid-state lighting in the form of light emitting diode lamps is quickly taking over the world as replacements for existing lower efficiency lamps. The lighting standards, which phased in from 2012 to 2014, do not ban incandescent or any specific lamp type, but they do require that lamps need to use about 25% less energy. The bipartisan Energy Independence and Security Act of 2007 (EISA 2007) established these efficiency standards. Many commercial lamps meet these new standards, including halogen incandescent filament, CFLs, and LEDs. The new bulbs provide a wide range of choices in color and brightness, and many of them last much longer than traditional lamps. However, the spectral distribution of flux from some of these new lamps do not match or even correspond to the spectral power distribution of traditional office and home lighting. In this review, the impact of the new lamp lights on the design, marketing, and production of modern decorative coatings is assessed. The decorative coatings industry has followed recommended guidelines for many decades, producing color-matches that are acceptable under a series of standard illuminants (D65, CWF, A) which are representative of the lamp lights in most common facilities. The new solid-state lamps do not render object colors in ways similar to the currently adopted standardized illuminants. The primary obstacle to the coatings manufacturer is the lack of standards on how to test color-matches for quality conformance under the new lamp lights. As the energy efficient lighting industry is currently still in a technologically developing phase, it appears that it will be some time before any agreements on the characteristics of modern lamp light will be reached. Therefore, guidance is provided on creating and/or using illuminant data representative of these lamps until official reference illuminants are published.

Intercomparison of high-resolution color measurements with similar and dissimilar geometric conditions

CORM Technical Subcommittee OP-1 under Optical Properties of Materials, has undertaken a round-robin inter-comparison of several industrial laboratories. The basis of the inter-comparison is similar to that reported by Verrill and by Rich in that the Ceramic Colour Standards were shipped from one laboratory to the next. There were six participants in this inter-comparison, all possessing at least one instrument capable of reading the spectral diffuse reflectance factor from 360nm to 780nm at 5nm intervals with a 5nm bandpass, as recommended in Publication CIE 15.2. The laboratory temperature was recorded and kept to within 2° C of the nominal target. Some laboratories had second instruments with slightly different realizations of the CIE recommended geometry for diffuse reflectance factor. The results compare the readings from similar instruments (same manufacturer and geometry) and dissimilar instruments (same spectrometer but different geometry or different spectrometer and different geometry). This represents the first time that an inter-comparison of both similar and dissimilar spectrophotometers and reflectance accessories can be reviewed simultaneously.