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Turn Out the Lights: How Does Night Vision Work?

Everyone has found themselves in a dark room, at one point or another, whether it be during childhood, due to a power outage, or just waking up in the middle of the night. It takes a few minutes for your eyes to adjust to the dark. This process, ''dark adaptation,'' causes us to adjust to the dark.

In order for night vision and dark adaptation to happen, several physiological, neurological and biochemical mechanisms have to take place behind the scenes. Let's have a closer look at how your eye actually operates in these conditions. Your eye uses two kinds of cells: cones and rods, which are found at the back of the eye; or, to be precise, on the retina. Together they form the sensory layer that helps the eye detect colors and light. Cones and rods are found throughout your entire retina, except for in the small area opposite the pupil known as the fovea, where there are only cone cells. The fovea provides detailed vision, for example when reading. You may have learned that the details and colors we see are sensed by the cones, and the rods allow us to see black and white, and are light sensitive and detect movement.

Considering these facts, if trying to find something in the dark, it's much more efficient to focus on the area 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.

Furthermore, the pupils dilate in response to darkness. It takes approximately one minute for your pupil to fully enlarge; however, it takes approximately half an hour for you to achieve full light sensitivity.

You'll experience dark adaptation when you walk into a darkened movie theatre from a bright lobby and have trouble finding a seat. But soon enough, you adapt to the dark 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. Keep looking; as you dark adapt, the stars will gradually appear. Despite the fact that your eyes require several moments to adapt to the dark, you will immediately be able to re-adapt to exposure to bright light, and this resets any dark adaptation that had developed where it was darker.

This is actually one reason behind why so many people prefer not to drive when it's dark. If you look directly at the lights of an approaching vehicle, you are briefly unable to see, until that car passes and you readjust to the night light. A good way to avoid this is to avoid looking directly at the car's lights, and instead, try to allow your peripheral vision to guide you.

If you're having trouble seeing when it's dark, book an appointment with our doctors who will check that your prescription is up to date, and rule out other reasons for worsened vision, such as cataracts and macular degeneration.

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