Study on Optimal Optical-Thermal Design of LEDs Applied for Automotive Lighting

In this paper, the state-of-the-art applications of LEDs (light emitting diodes, LEDs) used on automotive lighting have been summarized, including amber, red, and white LEDs. In the related applications, the increased luminous flux with the increasing of drive current and the resultant high junction temperature caused by the drive current increasing are two important factors and have been also investigated separately. According to the different luminescence mechanism of LEDs with different color, the change rules of both luminous flux improvement owing to the increasing of drive current and the drop of luminous flux originated from high junction temperatures were investigated by the liner analysis method based on the thermal simulation results. Tuning current is an effective method to increase the luminous flux during the simulation process, because the influence of junction temperature raising rate is much lower than that of current improvement for all LEDs. Otherwise, the changing gradient of luminous flux vs. power for red LED has a much higher value of about 1.26 than that of white LED, which is only about 0.19. Besides, the temperature difference of solder point and test point was investigated and results showed that the maximum difference of white LED is 4.4 K/W, which means the thermal resistance of case-to-solder cannot be neglected during the real sample test procedure.