Everyone's found themselves in a dark room, at one time or another. It takes a few minutes for your vision to return. This is called ''dark adaptation'' and it's what helps our eyes get used to low light settings.
Many people don't know that night vision relies on several physical, neural and biochemical mechanisms. Let's talk about how all this operates. Your eye features two kinds of cells: cones and rods, which are found on the retina at the back of the eye. Together they make up the sensory layer. This is the part that helps the eye pick up light and color. These cells are spread throughout your retina, except for in the small area opposite the pupil known as the fovea, where there are only cone cells. The fovea is primarily responsible for detailed sight, for example when reading. As you may know, the cones contribute to color vision, while rod cells help us visualize black and white, and are light sensitive.
Considering these facts, if you want to see something in the dark, like the edge of the last stair in a dark basement, it's more efficient to see it through your peripheral vision. When you do that, you use the part of the eye that has rods, which, as mentioned above, are more responsive to light, even if there isn't much of it.
Also, the pupils dilate when it's dark. The pupil grows to it its maximum size in about a minute; however, your eyes will continue to adapt over a half hour period and, as everyone has experienced, during this time, your ability to see in the low light setting will increase remarkably.
Dark adaptation occurs when you go from a very light-filled area to a dim one for example, walking inside after being out in the sun. Even though you need several moments to get used to the darker conditions, you will immediately be able to re-adapt upon re-exposure to bright light, but then the dark adaptation process will have to begin from scratch if you go back into the dark.
This is actually one reason behind why so many people don't like to drive when it's dark. If you look at the ''brights'' of an approaching vehicle, you are briefly blinded, until that car is gone and you readjust to the night light. To prevent this, try not to look right at the car's lights, and learn to try to allow your peripheral vision to guide you.
If you're beginning to find it increasingly difficult to see when it's dark, schedule an appointment with your eye doctor who will explore the reasons this might be occurring, and eliminate other reasons for worsened vision, such as cataracts and macular degeneration.