Visibility of Laser Beams and Illuminated Delineator as a Function of Fog Density

Abstract

In dense fog, adequate visibility of the delineator is important for providing the driver with road geometry cues. A new illuminated delineator that uses laser beams is proposed. Very few data have been published with regard to the visibility of laser beams in fog. However, laser beams can be expected to be highly visible in dense fog because of their high intensity, high energy, and directivity that is both monoclinic and strong. A study was conducted to evaluate the visibility of laser beams in fog. The effectiveness of two types of laser heads and an illuminated delineator containing two 10-W glow lamps was investigated in artificial fog. The dependent variables were luminance at a specific point on the laser beam and estimated brightness. The major independent variables were fog density and illuminance in the observation room. The laser beams were observed as sharp lines of light in dense fog. The visibility of the laser beams in fog had an inverse relationship to that of normal light. In addition, subjects reported that the directivity of the laser beams could effectively indicate the direction of the highway. However, the visibility of the laser beams was strongly affected by the illuminance in the observation room, and care must be taken to prevent drivers from looking directly at redundant laser beams. On the basis of these results, it is concluded that laser beams may be useful lighting sources in dense fog if this safety problem can be overcome.