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Home » What's New » Turn Out the Lights: How Does Night Vision Work?

Turn Out the Lights: How Does Night Vision Work?

Everyone has found themselves in the dark, at some point in their lives. You notice that it is difficult to see anything for several moments before your vision returns. This process is known as ''dark adaptation''.

Many people don't know that night vision relies on the cooperation of physical, neural and biochemical mechanisms. Let's have a look at how all this operates. The human eye takes in various forms of light using two kinds of cells: cones and rods, on the retina at the back of the eye. Together they form the sensory layer. This is the part that helps the eye pick up light and color. Cones and rods are distributed evenly throughout the retina, with the exception of the small area opposite the pupil known as the fovea, where there are only cone cells. That part is primarily responsible for detailed vision, such as when reading. You may have heard that the details and colors we see are sensed by the cones, and rod cells allow us to see black and white, and are light sensitive and detect movement.

Now that you know some background, let's relate it to dark adaptation. If you want to see something in the dark, like the dresser in your darkened room, you'll be better off if you view it through the side of your eye. Since there no rods in the fovea, you'll see better if you avoid using it when it's dim.

Another way your eye responds to the dark is by your pupils dilating. Your pupil grows to it its maximum size within 60 seconds; however, it takes about 30 minutes for the eye to fully adapt.

Here's an example of dark adaptation: when you exit a bright area and enter a dim one, for example, when you go inside after being out in the sun. It'll always require a few moments until you begin to adapt to normal indoor light. If you go back into the brightness, those changes will be lost in a moment.

This is actually one reason behind why a lot people prefer not to drive at night. When you look directly at the headlights of an oncoming car, you may find yourself briefly blinded, until that car passes and you readjust to the night light. A helpful way to avoid this is to avoid looking right at headlights, and instead, use your peripheral vision to observe oncoming traffic at night.

If you're beginning to find it increasingly difficult to see at night or in the dark, call us to schedule a consultation with your eye care professional who will explore the reasons this might be happening, and eliminate other and perhaps more serious reasons for poor night vision, like cataracts and macular degeneration.