## 3 Results
### Reflectance Values at a Wavelength of 700-1100 nm  
Table 9 presents selected descriptive statistics of the reflectance at a wavelength of 700-1100 nm. In the assessment of differences in reflectance values at subsequent time points (before oil application, after 20 min, and after 60 min), there was no statistically significant difference (\(p\) = 0.0591) between particular time points for the reflectance at a wavelength of 700-1100 nm after the application of Oil A. The results of multiple tests (Table 10) confirm the absence of differences at all time points of the reflectance assessment at a wavelength of 700-1100 nm after the application of Oil A. In the assessment of differences in reflectance values at subsequent time points (before oil application, after 20 min, and after 60 min), a statistically significant difference (\(p\) = 0.0003) was found between particular time points for the reflectance at a wavelength of 700-1100 nm after the application of Oil B. It was found that at a wavelength of 700-1100 nm after the application of Oil B (Table 10), the value of the reflectance after 120 min of exposure was statistically significantly higher compared with the value before, after 20 min, and after 60 min of exposure, and the value of reflectance after 60 min of exposure was statistically significantly higher compared with the value after 20 min of exposure. In the assessment of differences in reflectance values at subsequent time points (before oil application, after 20 min, and after 60 min), a statistically significant difference (\(p\) = 0.0040) was found between particular time points for the reflectance at a wavelength of 700-1100 nm after the application of Oil C. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Wavelength:** & & & & & & & & \\
**700–1100 nm** & **Variable** & **Mean** & **Median** & **Min.** & **Max.** & **Q 25\%** & **Q 75\%** & **Standard** & **Shapiro–Wilk** \\ \hline Oil A before & A\_0 & 0.527 & 0.552 & 0.345 & 0.614 & 0.522 & 0.561 & 0.078 & \(p\) = 0.0002 \\ \hline Oil A after 20 min. & A\_20\_min & 0.530 & 0.548 & 0.318 & 0.625 & 0.522 & 0.572 & 0.075 & \(p\) = 0.0005 \\ \hline Oil A after 60 min. & A\_60\_min & 0.560 & 0.559 & 0.341 & 0.694 & 0.548 & 0.583 & 0.065 & \(p\) = 0.0004 \\ \hline Oil A after 120 min. & A\_120\_min & 0.570 & 0.572 & 0.373 & 0.687 & 0.550 & 0.612 & 0.063 & \(p\) = 0.0261 \\ \hline Oil B before & B\_0 & 0.528 & 0.549 & 0.357 & 0.608 & 0.528 & 0.570 & 0.074 & \(p\) = 0.0002 \\ \hline Oil B after 20 min. & B\_20\_min & 0.530 & 0.547 & 0.343 & 0.604 & 0.523 & 0.560 & 0.065 & \(p\) = 0.0002 \\ \hline Oil B after 60 min. & B\_60\_min & 0.559 & 0.559 & 0.341 & 0.667 & 0.546 & 0.589 & 0.063 & \(p\) = 0.0008 \\ \hline Oil B after 120 min. & B\_120\_min & 0.570 & 0.572 & 0.322 & 0.657 & 0.555 & 0.610 & 0.070 & \(p\) = 0.0004 \\ \hline Oil C before & C\_0 & 0.525 & 0.543 & 0.334 & 0.589 & 0.523 & 0.575 & 0.076 & \(p\) < 0.0001 \\ \hline Oil C after 20 min. & C\_20\_min & 0.525 & 0.540 & 0.356 & 0.601 & 0.524 & 0.560 & 0.069 & \(p\) = 0.0003 \\ \hline Oil C after 60 min. & C\_60\_min & 0.560 & 0.561 & 0.335 & 0.661 & 0.546 & 0.580 & 0.065 & \(p\) = 0.0004 \\ \hline Oil C after 120 min. & C\_120\_min & 0.567 & 0.572 & 0.329 & 0.661 & 0.547 & 0.609 & 0.069 & \(p\) = 0.0009 \\ \hline Oil D before & D\_0 & 0.527 & 0.546 & 0.358 & 0.592 & 0.523 & 0.572 & 0.072 & \(p\) = 0.0001 \\ \hline Oil D after 20 min. & D\_20\_min & 0.524 & 0.547 & 0.328 & 0.600 & 0.520 & 0.570 & 0.079 & \(p\) = 0.0001 \\ \hline Oil D after 60 min. & D\_60\_min & 0.558 & 0.557 & 0.350 & 0.659 & 0.538 & 0.585 & 0.062 & \(p\) = 0.0023 \\ \hline Oil D after 120 min. & D\_120\_min & 0.569 & 0.571 & 0.346 & 0.665 & 0.543 & 0.611 & 0.066 & \(p\) = 0.0038 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Selected descriptive statistics of the reflectance value at a wavelength of 700–1100 nm, along with a statistical assessment of the normality of distribution.