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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

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Publication Number: FHWA-HRT-04-145
Date: December 2005

Enhanced Night Visibility Series, Volume XIV: Phase III—Study 2: Comparison of Near Infrared, Far Infrared, and Halogen Headlamps on Object Detection in Nighttime Rain

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The primary focus of this research was to evaluate the discomfort and disability glare associated with different sets of oncoming headlamps, including conventional halogen headlamps as well as newer high intensity discharge designs and their associated beam distributions and intensities. The visual performance portion (i.e., disability glare) of the study evaluated the ability of each headlamp to allow oncoming drivers to detect pedestrians on the right or left side of the roadway. This portion of the study looked specifically at how oncoming glare affects detection distances. Drivers also rated the discomfort glare using the deBoer scale while approaching each of the five sets of headlamps.(9) This portion of the study was performed to better understand how drivers subjectively perceive these headlamps. Overall, this study empirically broke down the oncoming glare of four categorically different HID headlamp designs and one halogen beam design. This effect was measured by pedestrian detection distance, discomfort glare rating, and illuminance level at the driver’s eye.

With the introduction of HID headlamps on the roadways, many issues have arisen because of the higher luminous output and unique—and sometimes discomforting—appearance these headlamps have. Drivers state that passing these HID headlamps on the road at night is not only irritating and discomforting but also unsafe. Although it is important to understand the implications of discomfort glare on roadways at night, disability glare is the bigger issue related to safety. When comparing data from this study with data previously collected in the ENV clear study (ENV Volume III), it appears that disability glare led to a 50-percent reduction in pedestrian detection distance. This study produced the following conclusions:

  • Results showed similar findings for both discomfort glare and disability glare for the VESs. The VESs that were rated as more discomforting were the same VESs that allowed shorter detection distances.

  • Although participant age did not cause a difference in discomfort glare ratings, the pedestrian detection distance significantly decreased as participant age increased.

  • The right pedestrian location yielded a detection distance almost twice that of the left pedestrian location. Not surprisingly, the left pedestrian location had almost twice the illuminance at the driver’s eye at the point of detection when compared to the right.

  • Beam intensity, or the maximum output of the headlamp, had more of an effect on disability and discomfort glare than beam pattern. VESs with higher maximum output were rated as more discomforting, and they were associated with shorter pedestrian detection distances than VESs with lower maximum output.

  • Beam width was a better indicator of illuminance levels at the detection point than the maximum intensity of the glare source.

  • Adaptation level from 0.15 lx to 0.45 lx had little effect on the glare rating, detection distances, and the illuminance at the driver’s eye at the detection point.


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