## 2 Materials and Methods
### Evaluation of Carpet Color Appearance under Different Illuminants  
In order to objectively evaluate the carpet color appearance, Datacolor(r) Check 3 Spectrophotometer, Lawrenceville, NJ, USA was used to measure the color parameters of the dyed carpets. Color parameters were addressed via the CIELAB scale. According to the CIELAB scale, three color dimensions were selected: Lightness/Darkness (L*), Redness-to-Greenness (a*), and Yellowness-to-Blueness (b*), to quantify the color appearance. CIELAB color space is a three-dimensional scale (Figure 2) addressing the unique colors of human perception: red, green, blue, and yellow. L* values range from 0 to 100, referring to black towards diffusive white. a* and b* values do not have any theoretical limit. However, for computational purposes, they are limited to \(-\)128 to 127. Positive a* values refer to red, while negative ones are assigned to green. Positive b* values are assigned to yellow and negative ones are assigned to blue. According to the International Commission on Illumination (Commission Internationale de l'eclairage, CIE), a change in this color system will result in a similar change of perceived color. The CIELAB scale is specially designed to address human color perception by efficiently addressing the slight changes in color hues. CIELAB space can address a wider color range than RGB or other color spaces. Hence, this scale is more effective in addressing human color perception than the RGB scale commonly used in computer graphics [29; 30]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Dyeing Protocols** & **Dye Bath Preparation** & **Improving Dye Take Up** \\ \hline
**Chemicals** & **Water** & **White vinegar** & **Common Salt** & **White vinegar** \\
**14 LI/lbs** & **165 mL/lbs** & **15 gm/lbs * & **100 mL/lbs** \\ \hline Required amount & 9.52 L & 112.16 mL & 10.2 gm & 68 mL \\ \hline \hline \end{tabular}  
* Powdered chemicals were measured in gm scale as per batch weight in lbs.
* 1 gm = 0.0022 lbs.  
\end{table} 
Table 4: Amount of chemicals required for the dye bath for dyeing one batch of carpets. Corresponding batch weight \(\approx\) 308.6 gm. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Shade** & **Light** & **Medium** & **Dark** \\ \hline
**Dye Concentration in the Dye Bath** & 0.08 g/Liter & 0.32 g/Liter & 0.62 g/Liter \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Dye concentration in the dye bath. Figure 1: Undyed and Dyed carpets; images were taken under CWF illuminant (**a**) carpet 1, (**b**) carpet 2, (**c**) carpet 3, and (**d**) carpet 4 (pictures resolution: 4032 \(\times\) 3024 pixels). For measuring the color appearance, samples were preconditioned at 21 \(\pm\) 1 \({}^{\circ}\)C (70 \(\pm\) 2 \({}^{\circ}\)F) and 65 \(\pm\) 2% RH for 24 hrs. After the preconditioning, the spectrophotometer was used to measure the CIE L\({}^{*}\), a\({}^{*}\), and b\({}^{*}\) values for a specific illuminant. Three color measurements were taken in three different places, diagonally aligned across the specimen. The three measurements were averaged for each of the L\({}^{*}\), a\({}^{*}\), and b\({}^{*}\) values. To realize the research agenda, the CIE L\({}^{*}\), a\({}^{*}\), and b\({}^{*}\) values were measured and averaged for three different illuminants. The illuminants are A (incandescent), D65 (noon daylight), and F02 (cool white fluorescent). For every illuminant, 10\({}^{\circ}\) observer systems were considered. Corresponding correlated color temperatures (CCT) and color render index (CRI) are charted in Table 6. Color rendering index refers to the illuminant's ability to depict the actual color of an object compared to a reference illuminant, while Color temperature uses numerical values to determine the color characteristics of a illuminant across a spectrum from warm to cool hues measured in degrees Kelvin (K) [31; 32]. A higher value corresponds to a cooler color, i.e., blue. A lower value corresponds to a warmer color, such as yellow.