Spectral Effects of LED Forward Lighting: Visibility and Glare

Light emitting diode (LED) forward lighting systems are rapidly being developed and will soon be on the road. One aspect of LED systems that will differ significantly from traditional halogen and high intensity discharge (HID) systems is their spectral power distribution (SPD). Of interest is how the new SPDs offered by LEDs will affect the visibility and comfort of drivers.

Recent studies have shown that headlamp sources that have more energy in the short wavelength region of the visible spectrum might result in increased discomfort to opposing drivers. Calculations were performed on LED sources to determine their relative potential to cause discomfort. Additionally, a field study was performed to determine the importance of discomfort and disability effects when LED sources are used in forward lighting systems as might be seen in practice. The results of these calculations and the field study are presented.

Studies have also shown that headlamp sources that have more energy in the short wavelength region of the visible spectrum provide benefits to the vehicle operator in off-axis target detection. Calculations were performed on a series of LED SPDs to determine their potential to stimulate rod photoreceptors. It was found that most of the LED sources analyzed can theoretically result in increased off-axis visual performance as compared to halogen and HID sources. The results of these calculations are presented and compared to field studies of headlamp spectra to determine the magnitude of these effects as potentially seen in practice.