*Article* **A Comparison of Two Different Light Booths for Measuring Color Difference of Metameric Pairs**

**Azmary Akter Mukthy \* , Michal Vik and Martina Viková**

Department of Materials Engineering, Faculty of Textile Engineering, Technical University of Liberec, Studentská 1402/2, 461 17 Liberec, Czech Republic; michal.vik@tul.cz (M.V.); martina.vikova@tul.cz (M.V.) **\*** Correspondence: azmary.akter.mukthy@tul.cz

**Abstract:** A standardized source of light is essential for visual color assessments, which is why lighting booths were developed. For the best results in visual assessment, it is important to consider the right choice of light source, the right viewing conditions, and the variability of the viewer. To date, many light booth technologies have been introduced to meet user demands. Since most of the light sources on the market are characterized by the designer or manufacturer, the resulting variations from booth-to-booth remain. In this study, we compared the performance of two standard light booths to assess the color difference of eleven metameric pairs. In this study, we checked an earlier technologybased light booth that is still used in the textile industry and contains illuminant A (Tungsten lamp) with CCT 2700 K, TL84 (tri-band fluorescent tube) with CCT 4000 K, and simulator D65 (CCT 6500 K) with a different light booth whose original light sources have been replaced by currently available LED retro kits from equivalent CCTs. As an inexperienced customer or industrial user, our question was, how important is this replacement? The results revealed that two different standard lighting technologies with similar CCTs cannot reproduce the same estimates because the light sources produced different SPDs. It is illustrating that caution is necessary when comparing results obtained from two different light booths containing light sources with similar CCTs but different SPDs. This comparative study suggested that the variability of the light sources' SPDs or the observer or the sample should be modeled considering light booth's technology to estimate its contribution to the overall variability. The close relationship between perceived and CAM02-UCS suggests that if both booths are used after the light sources have been calibrated, a formula based on color appearance models must be used to predict color appearance. To obtain better agreement between perceived and calculated color difference, one must need to avoid light booths with nominally white light sources.

**Keywords:** light booth; metameric pairs; visual assessment; gray scale; standard deviation; CAM02- UCS; color difference formula
