## 3 Results and Discussion
### Characterizing the Color Appearance of Carpets under Different Illuminants
#### 3.1.1 Illuminant 01: Noon Daylight (D65/10)
Carpet 4 has two variations (0.3125 and 0.375 in) in loop heights (Table 1) (Figure 4d). For addressing the chroma and hue of the dyed carpet in terms of CIE a and CIE b scales, similar decreasing trends as L* values were observed from light to darker shades (Figure 3c-f). For the red and green-colored carpets, reflected light mainly contains red and green associated wavelengths (620-780 nm) in the visible wavelength region. As previously discussed, a higher concentration of colorant molecules will result in more absorption of incident light for a certain wavelength. Hence, from light to dark shades, more absorption of corresponding red and green wavelengths occurred, which resulted in less reflection of the red and green light spectra along with other color wavelengths, which reduces the chroma values of a* and b*. Considering the variations in the a* values due to carpet features, the dark shades have identifiable variations (\(p<0.05\)) for all of the shades in both colors (Figure 3c,d). This could be related to less light reflection in all of the wavelength regions with increased concentrations of colorant molecules. For the dark shades, all wavelengths' light reflection decreased with colorant concentration. However, as the colorant molecules reflect the  
Figure 4: sketches of carpet loop structure (**a**) carpet 1, (**b**) carpet 2, (**c**) carpet 3, and (**d**) carpet 4.  
specific light wavelength associated with perceived color, the reduction in its reflection is less compared to the other light wavelengths. As the function of the colorant molecules is to reflect the light of the perceived color, this resulted in better hue distinction. Hence, the variation among the carpets in a* values become significant in the dark shade. For carpet 3 (Figure 3c,d), \(\mid\pm\)a\(\mid\) values are higher in the dark shade due to more colorants being present in the smooth reflective surface. Hence, more colorants in the horizontal yarn planes of the loops showed better chroma compared to the others. Carpet 2 has the lowest values for \(\mid\pm\)a\(\mid\), which is due to its high scattering of the reflected red / green light spectra resulting from the comparatively high twisted yarns in the loops (Figure 3c,d). Addressing the b* scale refers to the measurement of the secondary (non-dominant) hues from the reflected wavelength of light and their chroma as the carpets were dyed in red and green colors. For the red-colored carpets, significant (\(p<0.05\)) variations in b* values have been observed in the dark shade (Figure 3e) due to the carpet features. In this case, the reason is the same as before. More concentration of colorant molecules in the carpets enhanced absorption of all light wavelengths. However, less absorption of the red color wavelengths (due to the colorants' function), and consequently, better hue distinction of the reflected light, caused significant variations in b* values associated with different carpet features. Similar to the CIE a, the CIE b scale also documented higher values for carpet 3 and lowest for carpet 2 which was dyed in a red color with a dark shade (Figure 3e). As previously discussed, carpets' loop structure can affect +b values. Interestingly, in the case of green-colored carpets (Figure 3f), light and medium shades showed significant (\(p<0.05\)) variations in the +b values, apparently due to the carpet features, while the dark ones did not. The significant variations among the carpets in the lighter shades could be the combined effect of correspondent dye particles' absorption and reflection patterns of the visible light wavelengths and the carpet features. Following this, the dark shade is also expected to be significant as previously discussed. However, very low chroma of a yellow hue has been reported (\(\mid+\)b\(\mid\)\(<\) 4), indicating little to no reflection of the yellow/blue associated wavelengths. Hence, these substantially lower \(\mid+\)b\(\mid\) values cause the resultant insignificance in the dark shade among the carpet variations.