## 1 Introduction
Such thermal path media travel from the heat sink through the test box to the atmosphere via the air and plywood. However, the thermal conductivities of air and plywood are 0.024 W/m\(\cdot\)K and 0.13 W/m\(\cdot\)K at 25 \({}^{\circ}\)C. This causes high temperatures inside the test box, and increased junction temperatures. This study used this high temperature mechanism to verify the heat sink performance. The thermal resistance findings are illustrated in Figure 2. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Case**} & **Heat sink** & **Height (mm)** & \multicolumn{3}{c}{**Before**} & \multicolumn{2}{c}{**After**} \\ \cline{3-8}  & **Heat sink** & **Height (mm)** & \(T_{\text{sp}}\) (\({}^{\circ}\)C)** & \multicolumn{2}{c}{**Temperature Difference (\({}^{\circ}\)C)**} & \multicolumn{2}{c}{**Temperature Difference (\({}^{\circ}\)C)**} \\ \hline \multirow{3}{*}{1} & ALFHS & 17 & 87.0 & Higher & 0.4 & 100.1 & Higher & 8.4 \\  & CUFHS & 17 & 86.6 & & & 91.7 & \\ \cline{1-1}  & ALFHS & 20 & 85.0 & & & 94.5 & Higher & 2.8 \\ \cline{1-1}  & CUFHS & 17 & 86.6 & Higher & 1.6 & 91.7 & \\ \cline{1-1}  & ALFHS & 23 & 83.4 & & & 91.7 & \\ \cline{1-1}  & CUFHS & 17 & 86.6 & Higher & 3.2 & 91.7 & Same & 0.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison for heat sinks height determination. Effective cooling is particularly necessary in recessed fixtures, where ceiling insulation can obstruct the heat escape paths. The challenge, which can be addressed in different ways by numerous design strategies, is to maximize the capacity for heat to escape from the fixture for a given LED operating temperature. In this study, the thermal behavior of partially-recessed style lighting was modeled and measured in a configuration for a CLRDR. The thermal performance of the recessed fixtures was evaluated experimentally in a wooden box (i.e., the test box). The test box was used to emulate an insulated ceiling for testing purposes as in [14]. Light emission does not account for all power consumption. In high-power LEDs, approximately 25% of input power is converted to light. The rest is dissipated in the form of heat, causing the light extraction efficiency, emission intensity, and lifetime to decrease [15]. Poor thermal management may cause LEDs to fail in a few months, resulting in high LED junction temperatures [16]. Since high power LEDs are widely used in lighting fixtures, designing suitable heat sinks for maintaining a low LED junction temperature is particularly necessary. Temperature modeling according to the Arrhenius equation (Equation (1)) is widely used for reliability validation. This study examined CLRDLs by using an ALFHS and CUFHS installed in a small test box. While an LED is in operation, the temperature rises rapidly because of the heat generation from the P-N junction. The inner temperature of the test box was rapidly increased from the LED during the initial 2 h. The buoyancy flow results from density variations caused by temperature changes in different areas of the test box. This phenomenon can be observed both the numerical temperature distribution simulation and experimental results. In the test conditions, the LED junction temperature increase was markedly higher than it was in normal use conditions. The accelerated life test [17] was applied here to predict the CLRDL lifetime with accelerated ambient temperature was 55 \({}^{\circ}\)C.  
Figure 1: Illustration of the ALFHS or CUFHS mounted to the CLRDL after INST. Figure 2: Illustration of thermal resistance network for the CLRDL after INST. The Arrhenius equation predicts device lifetimes by modeling the relation between the increased temperature (temperature in testing) and the acceleration of the aging of a device as compared with its normal operational temperature (temperature in normal use). \[\mathrm{A.F.}=\exp\left[\frac{Ea}{k}\left(\frac{1}{T_{\mathrm{use}}}-\frac{1}{T _{\mathrm{test}}}\right)\right] \tag{1}\]