Imagine waking up in the middle of the night. It is dark, and there are other people still asleep in your house, so you do not want to turn the lights on and alarm them. But you are hungry, and you want a snack. You know that there are still some delicious brownies in the kitchen. You feel your way along the wall into the kitchen and enjoy the chocolate brownies in the middle of the night. With your late night craving satisfied, you are ready to return to sleep. But, before you return to bed, you may notice that after you have been up for a little while, you can see in the dark. What before was obscured, you can now discern. This is the process of dark adaptation. It takes nearly thirty minutes for the process to be complete, but the shift from photopic to scotopic vision allows people to see much better in the dark.
What is going on during dark adaptation? First, a definition: dark adaptation is the process in the visual system in which it increases its sensitivity to low light levels. During the first eight minutes of trying to see in the dark, it is still the cones that are doing most of your seeing. Then, your sensitivity to low levels of light increases, as your scotopic-system rods come online and start taking over.
In this illustration, you can explore the way that different receptors are important for dark adaptation.
To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.
On the Illustration tab, you can adjust the parameters to explore the changes in our sensitivity during dark adaptation.
Below is a list of the ways that you can alter the illustration. The settings include the following:
Normal Dark Adaptation : checking this box shows the general time course for dark adaptation
when the stimulus is large enough to stimulate the entire retina.
Cones Only: shows the theoretical function for dark adaptation of the cones only.
Rods Only: shows the theoretical function for dark adaptation for the rods only.
Fovea: checking this box shows the results for a dark adaptation experiment when the stimulus is small enough to only stimulate the fovea which only has cones. It will clear all other lines being displayed.
Periphery: checking this box shows the results for a dark adaptation experiment when the stimulus is small and stimulates far out in the periphery where there are very few cones. It will clear all other lines being displayed.
Pressing this button restores the settings to their default values.