This study was designed to investigate how the spectral power distribution (SPD) of LED headlamps (including correlated color temperature, CCT) affects both objective driving performance and subjective responses of drivers. The results of this study are not intended to be the only considerations used in choosing SPD, but rather to be used along with results on how SPD affects other considerations, including visibility and glare.
Twenty-five subjects each drove 5 different headlamps on each of 5 experimental vehicles. Subjects included both males and females, in older (64 to 85) and younger (20 to 32) groups. The 5 headlamps included current tungsten-halogen (TH) and high-intensity discharge (HID) lamps, along with three experimental LED lamps, with CCTs of approximately 4500, 5500, and 6500 K. Driving was done at night on public roads, over a 21.5-km route that was selected to include a variety of road types. Vehicle instrumentation was used to derive the measures of objective driving performance. After driving, subjects completed a set of subjective ratings.
The objective driving measures varied strongly with road type, but showed little if any effects of headlamp type. The subjective measures showed strong differences between the TH and HID lamps, but only small differences among the LED lamps related to CCT. There was a small tendency for higher CCT to result in more positive subjective ratings. Overall, the results indicate that effects of CCT on objective and subjective variables are not strong relative to the range of differences associated with roadway type.
