Eyewitnesses and Dark Vision

eyewitness-19061Question: An eyewitness has departed a brightly-lit café at mid-night and walked down a street dimly-lit by weak street lamps. 30 minutes after leaving the café, they witness a hit-and-run. The eyewitness has given a description of the incident and the vehicle involved to investigators. How would their account be expected to differ from a day-time incident? Would their report be more or less detailed if they had seen the hit-and-run only five minutes after leaving the café? Why?

Answer: Cone receptors in our eyes are adapted for colour vision, daytime and detailed vision, whereas rod receptors are adapted for vision in dim light. Dark adaptation is the gradual improvement in the ability to see in dim light, as the rod receptors (needed for the dark) regenerate their retinaldehydes (regenerating molecules) slower than cone receptors. This is how we can move into daylight (or a brightly-lit café) and our vision adjusts virtually straight away, as opposed to suddenly enter a dark area (dimly-lit street at mid-night). With this in mind, the eyewitness would be able to see clearer 30 minutes after leaving the café than if it were only 5 minutes after leaving as it takes between 5 – 30 minutes for full dark adaptation to occur.

Something to consider with eyewitness testimony in the dark is that colour perception after twilight is unreliable to non existent, and the Purkinje effect can change the relative brightness of colours (e.g. reds appear darker and blue-greens appear brighter) which can make testimonies more unreliable. Red light however does not interfere with scotopic (dark adapted) vision.

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About Bridget Dunn

A real estate professional since 2012, Bridget is known for integrity, diplomacy and sincerity in all her dealings. She has first and foremost strived to be someone in whom her clients and colleagues can put their trust and faith. Treating clients like family is both a guiding principal and way of life for Bridget. She is dedicated to listening intently to her clients needs and providing the best possible advice, from how to get the best sales result for their home, to matching individuals and families with the properties that best suit their needs.
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