## 3 Results and Discussion
### Characterizing the Color Appearance of Carpets under Different Illuminants
#### 3.1.1 Illuminant 01: Noon Daylight (D65/10)  
Figure 3 shows the resultant Lightness-darkness (L*), redness-greenness (a*), and yellowness-blueness (b*) values for four different carpets dyed with two different dyes (red and green) in three different shades (light, medium, and dark). As shown in Figure 3, the lightness values (L*) of the dyed carpet decreased from light to darker shades with increasing dye concentration. In the CIE L scale, lower L* values indicate a shift towards darkness, which refers to more light absorption in all the visible wavelength ranges. In this case, the L* values can be addressed via the Kubelka-Monk equation's \(K/S\) factor [35; 36; 37]. \[\frac{K}{S}=\frac{(1-R)^{2}}{2R} \tag{1}\]  
In Equation (1) \(K\), \(S\), and \(R\) refer to incident light absorption, scattering, and reflectance percentage, for a certain wavelength. According to the Kubelka-Monk theory, \(K/S\propto C\), where C is the concentration of colorant molecules. This equation refers to the proportional relationship between the C and \(K\)[38; 39; 40]. Therefore, a higher concentration of colorant molecules in the dyed substrate led to more light absorption and less reflection of all the visible wavelength ranges, resulting in a darker appearance and a lower L value. Hence, the L* value is inversely associated with the concentration of colorant molecules and the subsequent absorption of incident light. For these inverse relationships, the L* values of the dyed carpets decreased from light to dark shades with increasing dye concentration (Figure 3a,b). Comparing Figure 3a,b, only the green-light shaded carpets showed significant differences (\(p\) = 0.00383 \(<\) 0.05) for various carpet features, while the rest were found to be insignificant (\(p\) > 0.05). As shown in Figure 3b, the L* values of green-light shaded carpets are the highest among all the shades of red and green colored carpets. This means that  
Figure 3: CIE L*, a*, and b* values for D65/10 illumination of different carpets dyed in different shades of red and green color (**a**) L* values for red-colored carpets (**b**) L* values for green-colored carpets (**c**) a* values for red-colored carpets (**d**) a* values for green-colored carpets (**e**) b* values for red-colored carpets (**f**) b* values for green-colored carpets. the green-light shaded carpets have more reflection of the incident rays in all the visible wavelength ranges, resulting in higher lightness values. Such higher L* values could be related to the specific absorption trend of the dye molecules used for the green hue [41; 42]. Due to higher reflection of all the visible wavelength ranges, the difference between the L* values for the different carpet attributes becomes significantly different. On the contrary, the lower the L* values become, the less the effects of carpet attributes can be discerned on the lightness scale (CIE L), which explains the statistical insignificance found for red-colored carpets in all the three shades and green-colored carpets for medium and dark shade. In the green-light shaded carpets (Figure 3b), carpet 3 has significantly higher L* values compared to other types. Carpet 3 has wider loops due to a comparatively higher gauge and lower stitch rate. This indicates more horizontal yarn availability compared to the other loop-piled carpets selected for the methodology. Such horizontal yarn availability in the loop formation works as a smooth reflective surface, giving more light reflection in all the wavelength regions for higher lightness (L*) values [23; 25]. In the case of carpet 2, the L* values are the lowest. Carpet 2 has twisted yarn loops. The twisted structure on the horizontal portion of the loop causes more scattering and reduces the light reflection, resulting in lower lightness (L*) values. Figure 4 depicts the sketches of the corresponding carpets. Here, carpet 1 has small loops (Figure 4a), Carpets 2 and 3 have the same loop length, however, carpet 2 has more twists in the loops (Figure 4b,c).