Something wakes you up in the middle of the night, or you’re trying to find a light switch or door handle or phone in the dark. We’ve all found ourselves in the dark before. It takes a couple of minutes for your vision to return. This remarkable process is ”dark adaptation”.
Night vision involves a combination of biochemical, physical and neural mechanisms – for granted. So how does this work? The retina is a layer of cells at the back of the eye. The section of the retina behind the pupil that is responsible for the point of focus is called the fovea. The retina is made up of rod-shaped and cone-shaped cells. The rod cells are able to function even in low light conditions. Those cells are absent from the fovea. You may have learned that the details and colors we see are sensed by the cones, and rod cells help us visualize black and white, and are light sensitive and detect movement.
So, if you want to see something in the dark, like a small star in a dark sky, it’s better to look at something off to the side of it. That way, you’re avoiding the use of the fovea, which only has cells that are less sensitive to low light.
The pupils also dilate in low light. It takes less than a minute for the pupil to fully enlarge; however, dark adaptation keeps enhacing your vision for the next half hour and, as everyone has experienced, during this time, your ability to see despite the darkness will increase remarkably.
Here’s an example of dark adaptation: when you first enter a dark cinema from a bright lobby and have a hard time locating a seat. But after a couple of minutes, you adapt to the situation and before you know it, you can see. This same thing occurs when you’re looking at stars at night. At the beginning, you can’t see very many. As you keep staring, your eyes will dark adapt and millions of stars will gradually appear. Despite the fact that you need a few noticeable moments to get used to the darker conditions, you will immediately be able to re-adapt upon returning to bright light, but if you return to the darker setting, your eyes will need time to adjust again.
This is actually why many people have difficulty driving at night. When you look at the headlights of a car heading toward you, you are momentarily blinded, until that car passes and you once again adjust to the night light. To prevent this, try not to look directly at the car’s lights, and instead, use peripheral vision in those situations.
If you’re beginning to find it challenging to see at night or in the dark, book an appointment with your eye doctor who will make sure your prescription is up to date, and eliminate other and perhaps more severe causes for poor night vision, like cataracts and macular degeneration.