## 6 Conclusions  
In this study, we first numerically investigated the improvement in heat dissipation performance using the heat sinks fabricated using SLM for a CLRDL under jet impingement cooling. An optimized surface area for TTFHS was designed as a benchmark. Nine cases were developed to examine the heat transfer coefficient, Nusselt number, and thermal resistance. Experimental tests were conducted to validate the numerical simulation results. Some detailed specified temperature points for their temperature response were also measured. Under jet impingement cooling, the inlet air flow velocity, heat transfer surface area of heat sink, and heat sink geometries are the primary factors for heat transfer performance. Some concluding remarks are reached as follows. 1. Using the SLM approach, the PTFHS exhibited the highest heat transfer performance followed by the MFLHS and TTFHS irrespective of lower or higher Reynolds number turbulent air flow, because the PTFHS possesses increased heat transfer surface area and less air flow obstruction. Although MFLHS has increased heat transfer surface area, its heat transfer performance was less than the PTFHS because of its relatively narrow air flow channels obstructing heat exchange with the environment. 2. The proposed PTFHS and MFLHS increased the Nusselt number by 10.3% and 7.7%, reduced thermal resistance by 40.3% and 13.0%, and achieved weight reduction of 23.6% and 24.6%, respectively, based on comparisons of TTFHS. This enhanced the heat transfer rate and reduced the LED lighting module weight. Therefore, it allowed the CLRDL to increase LED power higher than 10 W for further light output requirement. 3. This study contributes to the applications of small or narrow spaces and a large heat removal requirement by applying jet impingement cooling. The numerical simulation results were consistent with experimental results. This consistency validated the approach of using the CLRDLs with PTFHS, MFLHS, and TTFHS under an environment with a high heat-source temperature and maintaining a low LED's junction temperature for ensuring LEDs longer lifetimes specified by Energy Star. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Type**} & \(\mathbf{T_{\mathrm{sp}}}\) & \(\mathbf{T_{\mathrm{j}}}\) & **Specified LED Limited \(\mathbf{T_{\mathrm{j}}}\)** & **Allowance of \(\mathbf{T_{\mathrm{j}}}\) to be Increased** \\  & (\({}^{\circ}\)C) & (\({}^{\circ}\)C) & (\({}^{\circ}\)C) & (\({}^{\circ}\)C) \\ \hline PTFHS & 39.4 & 69.4 & 135 & 65.6 \\ MFLHS & 41.5 & 71.5 & 135 & 63.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Temperature allowance for CLRDL when using relatively higher power levels LED. **Author Contributions:** Conceptualization, Y.-C.H. and H.-C.H. ; Formal analysis, Y.-C.H. and H.-C.H. ; Investigation, Y.-C.H. and H.-C.H. ; Methodology, Y.-C.H. and H.-C.H. ; Software, Y.-C.H. and H.-C.H. ; Validation, Y.-C.H. and H.-C.H. ; Writing--original draft, Y.-C.H. and H.-C.H. ; Writing--review and editing, Y.-C.H. and H.-C.H. All authors have read and agreed to the published version of the manuscript. **Funding:** Partial financial support from the MOST 108-2221-E-018-013 is appreciated. **Acknowledgments:** The authors would like to acknowledge the manufacturing of SLM (PITHS and MFLHS) made of ASIi0 Mg alloy from the Laser and Additive Manufacturing Technology Center, Industrial Technology Research Institute. **Conflicts of Interest:** The authors declare no conflict of interest. **Nomenclature**