## 1 Introduction  
Since 2010, car manufacturers have designed high-end vehicles with Light-Emitting Diode (LED) headlamps instead of traditional halogen lamps and high-intensity discharge (HID) bulbs. Halogen bulbs have the advantages of simple manufacturing, low cost, and the capability to illuminate far distances. However, they have disadvantages such as low luminous efficacy, short lifetime, and extremely high temperature. The correlated color temperature (CCT) is about 2600 K to 3200 K. The brightness of HID bulbs is three times that of halogen bulbs, the temperature of the lamp is between 300 \({}^{\circ}\)C and 400 \({}^{\circ}\)C, and the CCT is between 4000 K and 10,000 K. Both halogen bulbs and HID bulbs have the problem of high temperature. HID bulbs also have the risk of high-voltage electricity [1, 2]. In contrast, applying LEDs in automobile headlamps can improve the shortcomings mentioned above and has considerable advantages. Many automobile manufacturers design multi-zone lighting to make vehicles adaptable to various road conditions, such as the matrix LED headlamp of the AUDI [3], the multi-beam LED headlamp of BENZ [4], and the adaptive LED headlamp of BMW [5]. The headlamps can accurately distribute the light to improve safety in driving vehicles according to the various road conditions in urban areas, suburbs, and highways. The main purpose of using LED lamps in car headlamps is to reduce power consumption and heat generation, extend the bulb's lifetime, increase the illumination level, and meet the requirements of relevant laws and regulations [6, 7, 8, 9]. The ambient temperature hasa considerable impact on the luminous intensity and lifetime of the LED [10, 11]. Using the LED in the headlamp of a car is necessary to understand further the effect of the ambient temperature on the performance of the LED. The headlamps are installed on the left and right sides of the front of the car. Although there is a windward effect of removing the heat during driving, the internal combustion engine (ICE) generates much heat in the engine room. If the ambient temperature is 35 \({}^{\circ}\)C, the air temperature in the engine room is as high as 60 \({}^{\circ}\)C to 70 \({}^{\circ}\)C, and up to 80 \({}^{\circ}\)C at most [9]. Such high ambient temperature would significantly impact the performance of the LED chip of the LED headlamp [12, 13]. The junction temperature (\(T_{\rm j}\)) of the LED in automobile headlamps is high. Generally, the maximum temperature of \(T_{\rm j}\) is about 150 \({}^{\circ}\)C, and the limit on the temperature is 175 \({}^{\circ}\)C [14]. The higher ambient temperature is adverse to the heat dissipation of the LED lamps, which causes an increase in \(T_{\rm j}\) and affects the luminous intensity and lifetime of the LED chips [15, 16, 17, 18]. In recent years, many researchers have devoted themselves to solving the heat dissipation problem of LED chips through numerical analysis [16, 19, 20, 21] and experimental methods [22, 23, 24] and have achieved remarkable results. Important related references on heat dissipation of vehicle headlights are detailed below. [PERSON] et al. [19] used computational fluid dynamics to develop an air-cooled heat sink for LED headlamps and conducted experiments on a plate-fin type heat sink with a cooling fan for heat dissipation. The experimental results showed that the temperature of the soldering point \(T_{\rm sp}\) and the evaluated \(T_{\rm j}\) were 62.8 \({}^{\circ}\)C and 103.6 \({}^{\circ}\)C, respectively, \(T_{\rm j}\) lower than the maximum acceptable \(T_{\rm j}\). [PERSON] et al. [16] used ANSYS CFX 14 software to study the effects of fin design, fin materials, natural convection, and forced convection on \(T_{\rm j}\) in the cooling application of LED automotive headlamps under various ambient temperatures (25 \({}^{\circ}\)C, 50 \({}^{\circ}\)C, and 80 \({}^{\circ}\)C) and dissipated powers (0.5 W, 0.75 W, 1 W, and 1.25 W).