## 3 Experimental Design and Implementation  
Figure 2 shows the LED lamp used in the automotive headlamps (CCT 6000 K pure white LUXEON; LED-HL [\(\approx\)H4], PHILIPS, Shanghai, China) was used for testing in this study. Both sides of the lamp have four of the same LED chipsets (a chipset with three LED chips), and each side has two: one for the driving beam (hereafter called high beam) and the other for the passing beam (hereafter called low beam). There is a reflector under the low beam chipset to control the light distribution from the low beam chipset. The electrical specifications of this LED lamp have an input current of 1.2 A and power consumption of approximately 15.5 W when the supply voltage is 13.2 V (for both high beam and low beam). Each side for fixing the LED chipsets on the substrate has an aluminum rivet, and a thermocouple (1/0.2 mm \(\times\) 2C, T-type, accuracy: \(\pm\)0.75%) was installed here to measure the temperature of the substrate (\(T_{1}\)). Because of the excellent thermal conductivity of aluminum rivet, the temperature at this point represented the surface temperature of the substrates on both sides. In addition, a thermocouple was installed on the aluminum body (\(T_{2}\)) and the aluminum fin radiator (\(T_{3}\)) to measure the temperature at these locations. Furthermore, two thermocouples (\(T_{4}\) and \(T_{5}\)) were set up in the test space of the LED lamp to measure the ambient temperature (\(T_{a}\)) of the experiment. All thermocouples used were of the same form. Figure 3 is a schematic diagram of the experimental measurement system. The LED lamp was fixed on the test holder and placed in a fixed position in the air circulation temperature control oven (internal dimensions: W60 \(\times\) D50 \(\times\) H50; DH-600N, YOTEC, Hsinchu, Taiwan) to measure the illuminance, spectrum, and power consumption under various \(T_{a}\) (30, 40, 50, and 60 \({}^{\circ}\)C). The center of the low beam and high beam chipsets of the LED lamp was aligned with the air vent on the upper side of the oven through which the illuminance spectrum was measured, and the measurement distance was about 305 mm. The illuminance is proportional to the luminous flux, so the authors measured the illuminance to monitor whether the luminous flux changed. To avoid the stray light from the environment entering the measuring instrument, the vent was plugged into a black tube to absorb most of it. The tube has a length of 270 mm and a diameter of 25 mm. The illuminance of the LED lamp was measured by an illuminance meter (LX-103, Lutron, Taipei, Taiwan; accuracy: \(\pm\)5.0% + 2 digits) six times for each experimental parameter, and the average value was taken as the experimental data. The spectrum of LED lamps from 350 nm to 800 nm was measured using an optic fiber spectrometer (wavelength range: 200-850 nm; BRC112E-V QuestTMX, B&W, Plainsboro, NJ, USA) with an integrating sphere (\(\psi\) = 5 cm). To inspect the effect of \(T_{a}\) on the angular distribution of the luminous flux and spectrum, the illuminance and spectrum of the LED lamp were measured in three directions of the LED lamp (0, 90, 180 degrees) by rotating the fixture shaft. Referring to the inset in Figure 3, the direction '0 degrees' means rotating the LED lamp to let the LED chips on the right side face the upper air vent (in the y-direction), the direction '180 degrees' means rotating the LED lamp to let the LED chips on the left side face the upper air vent,  
Figure 2: Photograph of automotive LED lamp and schematic diagram of measurement position. and the direction '90 degrees' means rotating the LED lamp to let the normal of the LED chips parallel to the _x_-axis as shown in the current illustration of the inset.