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.
Light Adaptation occurs when light returns, such as when electric lights are turned on in an otherwise dark room. It is acceptable to think of light adaptation as being like dark adaptation, but in reverse. However, there is one major difference: light adaptation will be completed in about five minutes or even less, as the visual system switches back to relying on cones rather than rods. Dark adaptation is, therefore, much slower.
In this illustration, you can simulate what happens to your vision during dark and light 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 and start a simulation of dark adaptation.
Below is a list of the ways that you can alter the illustration. The settings include the following:
Enter a Dark Room : change the photograph to simulate going from a very bright
area, say outside in the noonday sun, to inside a very dark room where everything appears too dark.
Go Out Into the Bright Sun: change the photograph to simulate going from a dark room to outside in the bright sun.
Adjust Sensitivity: for less extreme changes in sensitivity, use this slider.
Use Your Own Image: allows you to upload your own image to do your dark/light adaptation simulations.
Pressing this button restores the settings to their default values.