Spectral Effects of High-Intensity Discharge Automotive Forward Lighting on Visual Performance

Recent studies have shown that high-intensity discharge (HID) headlamps provide visual benefits to the vehicle operator that may lead to increased nighttime driving safety. An experimental field investigation is described that further investigates the visual performance aspects of HID forward lighting systems to isolate and examine the role of lamp spectral distribution under realistic nighttime driving conditions.

This study examines lamp spectral distribution by direct comparison of HID source spectra to one that simulates a conventional halogen source. Two additional lamp spectra are also included in this study, a “cool” distribution with a high percentage of short wavelength visible light and a “warm” distribution with a high percentage of long wavelength visible light. Subjects perform a visual tracking task, cognitively similar to driving, while seated in the driver's seat of a test vehicle. Simultaneously, small targets located at various angles in the periphery are activated and target detection reaction time is recorded. Reaction times greater than 1 second are considered misses. Target illuminances are kept constant between the HID and halogen simulating systems, allowing the effects of spectrum to be identified and isolated.

From the results, comparisons are made among the four lighting conditions. The differences in visual performance as a function of light spectrum are discussed. The potential implications of the results on driving safety and on the development or refinement of HID forward lighting systems are also discussed.