# Advancing Sustainable Textile Metrology: Reflectivity Measurement with Controlled Light Sources
## 3 Results and Discussion
### Correlation Analysis  
An interesting possibility offered by the proposed method is to perform a correlation analysis between the reflectivity of textiles under different types of lighting.  
Figure 8: Correlation between the mean reflectance ratio (RR\({}_{\text{av}}\)) and its coefficient of variation (CV). Red dots indicate individual sample values; the red line shows the linear trend, and the shaded area represents the 95% confidence interval.  
Figure 9: Average reflectance ratios per lighting condition, calculated across all samples. Intended for general comparison of lighting effects, complementary to Figure 5.  
The graph in Figure 10 illustrates the relationship between reflectivity under daylight and fluorescent light for all textile samples. The correlation coefficient is 0.978, indicating a very strong positive relationship. The regression equation is as follows:  
\[FR=-0.0533+1.0351 DR \tag{5}\]  
where FR is the average value of the reflectance ratio of all samples under fluorescent store light, and DR is the average value of the reflectance ratio of all samples under daylight conditions.  
The colored area represents the confidence interval (CI) for the regression line (95%). This result shows that textiles (with the chosen reflective thread) with high reflectivity under daylight almost always reflect well under fluorescent lighting (in stores or industrial spaces). The narrow CI area indicates that the data are strongly correlated.  
Figure 11 shows the correlation between reflectivity under daylight and home lighting. Again, the line represents the regression relationship between reflectivity under daylight and home lighting, and the derived equation is as follows:  
\[HR=0.8385+0.3779 DR \tag{6}\]  
where HR is the average value of the reflectance ratio of all samples under home light.  
The correlation between daylight and home lighting is weaker compared to fluorescent lighting. The area in green is the 95% CI. It is wider, indicating that the differences between the samples are greater--some of them reflect very well under daylight but not as effectively under home lighting. Some samples have significantly lower reflectivity under home conditions, meaning that the type of light has a stronger effect on them.  
The conclusion is that home lighting has a stronger effect on reducing reflectivity compared to fluorescent lighting. Therefore, for indoor applications, additional tests should be conducted. For stable reflectivity in different environments, textiles that do not lose their properties under warm artificial light should be selected.  
Figure 10: Correlation between samples’ reflectivity under daylight and fluorescent lighting. Blue dots represent sample values, the blue line shows the regression trend, and the shaded area denotes the 95% confidence interval.  
It is interesting to make a comparison between the reflectivity of the samples under the two types of store lighting--Figure 12. The purple line represents the regression relationship between reflectivity under regular store lighting (store light) and fluorescent store lighting (store light fluorescent). The derived regression coefficient is as follows:  
\[FR=0.0123+1.0720 SR \tag{7}\]  
where SR is the average value of the reflectance ratio of all samples under regular store light.  
Figure 11: Correlation between samples’ reflectivity under daylight and home lighting. Green dots represent individual samples; the green line shows the trend, and the shaded area marks the 95% confidence interval.  
The narrow purple area of the confidence interval around the line indicates a strong correlation, meaning that the reflectivity under both types of store lighting is very similar. The conclusion is that with the chosen reflective thread, if the reflectivity under one type of store lighting is known, the reflectivity under the other light type can be accurately predicted. Fluorescent lighting slightly improves the samples' reflectance, but not enough to have significant practical implications.