Forward Vehicular Lighting and Inclement Weather Conditions

This paper summarizes research conducted to investigate the problem of forward visibility while driving during inclement weather. A review of the literature indicates that using narrow-distribution lamps, mounted away from the driver's line of sight, would result in the lowest amount of back-scattered light. The literature also indicates that the spectral content of light can influence glare and fatigue experienced while driving under these conditions. A series of investigations summarized in this paper confirm the review of the literature and appear to indicate that beam distribution and mounting position offer more leverage to vehicle designers than spectrum, for minimizing discomfort and glare while driving during adverse weather. Introduction and Background The essential problem with forward lighting while driving in inclement weather is that of reflected light from snow, rain and fog particles toward the vehicle driver. This reflected light decreases visibility by reducing contrast and by contributing to glare that can lead to fatigue and thus to a higher likelihood of accidents [1]. Visibility in falling snow might be worse than in fog, because the snow flakes present dynamic, rapidly flickering stimuli that may appear brighter than the more even distribution of reflected light in fog conditions [2,3]. Such phenomena could exacerbate discomfort or distraction while driving during inclement weather. Under conditions likely to be experienced by drivers during inclement weather, a review of the relevant literature [4,5] reveals four factors that appear to be most important in affecting visibility and distraction: light source mounting location [6-9], aiming angle [7,10], beam spread [9,11] and spectral power distribution (color) [7,12,13].