Visibility at Night & in Dark Environments

Exponent personnel evaluate and quantify human capabilities and limitations in perception and response, taking into account variables such as sources of ambient illumination, fatigue, age, expectancy of a hazard, level of distraction/inattention, visibility of a hazard, and the ability of the visual system to process and identify a potential hazard to avoid an accident. We have published on issues relating to human perception and performance under a variety of lighting conditions, ranging from the ability of drivers to perceive potential hazards to the influence of moon phase on visibility.

Our visual system is optimized for daytime activities, because it is most sensitive to high contrast objects, defined by differences in motion, color, size, etc. against the visual scene. At nighttime and in situations of low levels of illumination, our ability to perform optimally may be severely impaired. This is due to obvious reasons, such as decreased conspicuity of road hazards or pedestrians, but also due to physical and cognitive limitations of human perception and performance. This reduction in our performance may have severe consequences in almost any scenario that requires us to interact with our environment. Even seemingly simple tasks can become challenging to perform, e.g., driving along an illuminated street in a residential neighborhood, walking on a flat and unobstructed surface, attempting to hold or manipulate objects, etc.

In many situations, the level of light in the area of an accident is evaluated using a light meter. However, this quantitative measurement does not describe what an observer qualitatively experienced. To this end, Exponent personnel developed a highly customizable method of photography calibrated to capture and reproduce accurate representations of scenes in conditions of low illumination. Thus, this technique provides Exponent personnel with the unique opportunity to accurately demonstrate what an observer of a scene could have perceived at practically any given moment in time and from any perspective, e.g., the viewpoint of a driver approaching a darkly clad pedestrian crossing a street, or vice versa. This technique has been empirically validated, published, and admitted in multiple state and Federal courts. This service can be provided on short notice to document accident scenes immediately or in a site-inspection/re-creation environment. This same photographic technique can also be applied to non-vehicular matters, including slip/trip-and-fall accidents, evaluations of signage visibility, or any other situation requiring imagery of dimly lit environments.



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