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Night-time Visibility Studies


Often, two of the questions put forward in night-time motor vehicle collisions are, what could the driver have seen in the time leading up to the collision, and when could he or she have seen it?

These can be difficult things to assess, particularly if the lighting at the time of the incident was less than optimal. Resolution of these questions often entails a night-time visibility study.

It may seem reasonable to simply go to the site at the same time of the day that the incident occurred and, using either a regular or digital camera, take a picture. The photograph you get will show how things appeared, right? Unfortunately, this approach doesn’t work.

While the photograph will probably turn out, particularly in light of the photographic technology now available to us, such a photograph is almost never useful in demonstrating the visibility conditions that would have been present at the time of the incident. Consequently, such a simplistic approach is not appropriate when you need to determine what a driver who was involved in a collision could have seen.

To understand how a night-time visibility study works, one needs to understand that there is a difference between how eyes work and how cameras function. Photography involves passing light through a lens to expose photosensitive chemicals, producing a negative, and then using the negative to produce a paper image. However, the way a camera records an image is different from how the eye sees.

Within the eye, visibility is a function of two processes: sensation and perception. Sensation refers to the issue of whether the light from the object was sufficient to reach a physiological level needed for detection. Perception has more to do with the viewer’s attention, memory and other cognition functions. For example, an object might be detectable, but still not seen because the viewer’s attention was not engaged.

One of the goals of a visibility study focuses on sensation. The aim is to determine the lighting conditions present at the time of a motor vehicle collision in order to assess whether certain hazards should have been visible.

Sintra Engineering has developed a qualitative technique that accurately reproduces, in photographic form, the lighting, contrasts, and visibility levels that were present on the night of the incident in question. This technique calibrates the resulting photographic images by considering how and what our eyes actually see.

While other more quantitative methods of performing a visibility study exist, they more typically involve the assessment of the illuminance. The results from this type of visibility assessment can be difficult to understand and compare to the incident involved.

The photographs produced through our proven qualitative technique permit our clients to observe the visibility conditions present at the time of the incident without having to attend the scene or interpret complex illuminance parameters.


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