Cone cells contain rhodopsin, which is one of many light-sensitive chemicals. The cone cells themselves can adapt to partial darkness. All other colors that exist are experienced by humans as a mixture of red, green and blue. Human eyes have red-, green-, and blue-detecting cone cells. Similar to a grid of pixels in a digital camera, a vast spatial array of cone cells along the retina detect the different bits of colored light that make up the image we are seeing. The cones cells along the retina are responsible for color vision. The pupil's contribution to dark adaptation takes only a few seconds to a minute to be completed. This dilation lets as much light as possible into the eye so that sensitivity is enhanced. When confronted with low light conditions, the iris expands the pupil as wide as possible. The iris that surrounds the pupil contains muscles that control the size of the pupil. The pupil is the dark hole near the front of your eye that lets the light into your eye so that the light can form an image on the back (the retina). As described in the textbook Optometry: Science Techniques and Clinical Management, edited by Mark Rosenfield and Nicola Logan, the three main players in dark adaptation are the pupil, the cone cells, and the rod cells. There are several factors that contribute to our eyes adapting to darkness. Public Domain Image, source: Christopher S. The actual curve varies from person to person, from one spot on the eye to the next, and from one day to the next.
Note that this plot is only representative of the general trends. The rod cells can take several hours to become completely dark adapted and reach their peak sensitivity to low light conditions. The cone cells adapt within 10 minutes but then are overtaken in performance by the rod cells. Typical sensitivity of human eyes as they adapt to darkness.
But several hours into darkness exposure, the human eyes continue to adapt and make small gains in sensitivity. For this reason, many people think that after only a few minutes, their eyes have reached their peak sensitivity. The quickest gains in vision sensitivity are made in the first few minutes after exposure to darkness. Human eyes take several hours to fully adapt to darkness and reach their optimal sensitivity to low light conditions. With enough time, our eyes can adapt and see the low levels of light present in partial darkness. Most of our experiences with darkness are actually cases of partial darkness where there is still a small amount of light present.
City lights reflecting off of clouds, car headlamps, the moon, the stars, and even the airglow of the night sky itself all fill the night with faint light. With that said, it is quite rare to be in a situation with total darkness, even at night. Total darkness means the absence of light, and our eyes depend on light to see. Baird.įirst of all, it is impossible to see anything at all in total darkness.
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