## 1 Introduction  
The color appearance of teeth needs to be matched and reproduced by restorative dental materials to achieve acceptable aesthetic conditions. The ISO/TR 2864:2016 Dentistry--Guidance on Colour Measurement [1] describes visual and instrumental methods for assessment of subjects related to color shade and interconvertibility of monochromatic and polychromatic dental tissues and/or dental materials. Bearing this in mind, the characteristic of the light source (or illuminant) used to illuminate a given sample for a color measurement must be specified. The official illuminants used in colorimetry have been published by the _Commission Internationale de l'Eclairage_ (CIE) (see Abbreviations list in supplementary materials) [2]. This published set of illuminants includes spectral data approaching daylights and various incandescent, fluorescent, discharge, and LED lamps. Among all the descriptors of an illuminant, in particular, the spectral power distribution (SPD) and correlated color temperature (CCT) [2] are of utter importance for the experimental setup when evaluating color appearance of teeth and dental materials. A light source which represents noon daylight (CCT of 6500K) with a color rendering index (CRI) of 90 or greater is recommended when visual color assessments are made in dentistry [1]. In this context, it is important to point out that the color difference exhibited by a specimen across different viewing conditions is known as color inconstancy [3]. The CIE has been responsible for introducing the main color systems, illumination/detection geometries and color difference (\(\Delta\)E), and color appearance concepts used in color science [4]. When considering CIELAB color space, the CIELAB color difference \(\Delta E_{ab}^{*}\) has been the standard parameter employed by many users to measure total color difference. However, the CIE [2] recommend the use of the CIEDE2000 color difference formula (\(\Delta E_{00}\)) [5] because it provides a better fit than the CIELAB formula for visual color differences managed in many different industrial applications, including dentistry [6; 7; 8; 9]. In dentistry, visual judgments are the most frequently used method for evaluating color. Thus, adequate knowledge of the limits of the perception of colors in dentistry is crucial for understanding color differences in clinical dentistry [10]. Just perceptible refers to the lowest color difference that can be detected by an average human observer with normal color vision. A color difference noticeable by 50% of the observers corresponds to a 50:50% perceptibility threshold (PT). Similarly, the difference in color that is considered as acceptable for 50% of observers corresponds to a 50:50% acceptability threshold (AT) [11]. The visual color thresholds are of extreme importance in interpreting color differences in clinical dentistry and dental research [12; 13]. Several studies have established the value of color discrimination thresholds in dentistry [13] and, in particular, [PERSON] et al. [14] determined the values of CIEDE2000 color difference thresholds in dental ceramics (PT\({}_{00}\) = 1.25 and AT\({}_{00}\) = 2.23). General lighting is currently undergoing a revolutionary shift towards solid state devices, in particular light emitting diode (LED)-based technologies, as a replacement for classic fluorescent lamps. LEDs save energy and provide the same or better quality of illumination and visual comfort than classic fluorescent lamps. Researchers [15] investigated the perceived quality of LED sources in psychophysical experiments, considering color difference assessment and color appearance estimation. The results show that LEDs outperformed conventional fluorescent lamp-based simulators for the CIE illuminant D50. Furthermore, colorimetric measures revealed that LED simulators can achieve the desired quality according to the relevant ISO and CIE standards [16].