## 3 Measurement and Analysis Results  
In the course of the experimental research works, several measurement sessions were conducted in which the heating process of the lamp was recorded with the use of the thermal imaging camera. The images were taken at such intervals that it was possible to draw the lamp heating curve and then to determine the trend using non-linear regression. Figure 3 depicts example images gathered at the very beginning, after six minutes of operation (Figure 3a), and in the stabilized state, after about seven hours of operation (Figure 3b). Based on the gathered images, it was stated that the temperature distributes equally within the two heat sinks. The values are higher on the bottom heat sink, which dissipates the heat produced by LEDs as at the top heat sink. The lowest temperatures were registered in the central part of the lamp, which is made of plexiglass. The temperature around the object decreases rapidly with the distance and targets the ambient temperature. In Figure 4a, the temperature distribution on the lamp surface after eight hours of operation gathered from the computer simulations is presented. The distribution of heat calculated for the lamp surface corresponds to data gathered from measurements. In order to assess the quality of the calculated model, temperature values that were registered and calculated along the edge of the lamp surface and at a point defined as P2, as depicted in Figure 4b, were compared. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Description** & **Value for T** & **Value for L** & **Value for V** \\ \hline Maximum element size & 141 [mm] & 308 [mm] & 308 [mm] \\ Minimum element size & 42.4 [mm] & 13.2 [mm] & 13.2 [mm] \\ Curvature factor & 0.7 & 0.3 & 0.3 \\ Resolution of narrow regions & 0.6 & 0.85 & 0.85 \\ Maximum element growth rate & 1.2 & 1.35 & 1.35 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mesh settings for the tunnel (T), the lamp (L), and its vicinity (V). \begin{table}
\begin{tabular}{c c} \hline \hline
**Description** & **Value** \\ \hline Minimum element quality & 0.02403 \\ Average element quality & 0.6615 \\ Tetrahedral elements & 169,568 \\ Triangular elements & 13,294 \\ Edge elements & 1760 \\ Vertex elements & 121 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Mesh statistics. In Figure 5, the verification result is presented, which depicts temperature values measured (in blue) and calculated using the numerical model (in red) along the edge of the lamp on its surface established after 8 h of operation, thus in the steady state. In general, the waveforms of the curves are consistent and overlap. There are inaccuracies visible in the lower part of the lamp, at the rungs of the bottom heat sink, where temperature fluctuations in the range of 2 \({}^{\circ}\)C were recorded with the thermal imaging camera, whereas in the numerical model, these fluctuations were not observed. The temperature difference in this area is of 2.7% with a maximum value of 74.5 \({}^{\circ}\)C. In the transparent area of the plexiglass, the temperature values do not differ significantly. The temperature difference in the area of the top heat sink equals a maximum of 1.5 \({}^{\circ}\)C, which by a temperature equal to 57.5 \({}^{\circ}\)C implies a 2.6% deviation between the measured and calculated values. The overall error does not exceed 3%; therefore, it was assumed that it can be neglected, and the model has been positively verified. Figure 4: (**a**) Example image from simulation result depicting temperature distribution at the surface of the lamp in the steady state; (**b**) location on the edge of the lamp and at point P2 in the computational domain. Figure 3: Examples of images gathered from thermal imaging camera: (**a**) made after 6 min of operation; (**b**) made after 7 h of operation of the lamp. Figure 6 shows the transient and steady-state results of measurements and calculations.