Point of interest.
After reading about light and dark adaptation it should be clear that visual adaptation is a partial, up and down kind of process, with receptors constantly adjusting to variations in light exposure. If stimulation remained constant and the eyes adapted completely the result would be a loss of vision. In reality, the eyes never adapt completely because light is rarely focused on the same receptor continuously. Small involuntary movements of the eye keep the image moving slightly on the retina to prevent this from happening. |
Visual adaptation relates to the sensitivity of rods and cones based on the how much light is available.
Dark Adaptation is the process of increasing sensitivity to lowered levels of illumination. If you move from a well lit room to a darkened room, like a theater, initially it is very difficult to see. After about ten minutes your rods and cones will have adjusted; increasing their sensitivity to light. The cones will not adjust any further, the rods however continue to become more sensitive to the low levels of light reaching maximum sensitivity at approximately 30 minutes allowing you to see quite well in the dark. This can be difficult for example, when driving a car as the illumination within the car and oncoming headlights, conflict with the darkness outside and neither your rods or cones are able to completely adjust. Watch the averted vision video below for how astronomers deal with this adaptation issue. Light Adaptation is a much more rapid process. When moving from a darkened to bright room all receptors fire at once almost blinding you, causing you to squint or shield your eyes. Within about a minute the iris has contracted and your receptors have adjusted allowing clear vision. |
Dark AdaptationThis video was created with astronomy in mind yet can help us understand the process of sensory adaptation as it applies to eyesight.
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Averted VisonAstronomers provide insight into practical application of the knowledge gained in this module. Understanding concentration of Rods & cones combined with sensory adaptation assist star gazers as outlined in this video.
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