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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?

Picture this: there's a power outage and you've got to locate a flashlight or the fuse box. It takes a couple of minutes for your vision to return. We call this ''dark adaptation'' and it helps our eyes see in low light settings.

A person with a healthy set of eyes probably takes night vision - and the role of the biochemical, physical and neural mechanisms - for granted. Let's have a closer look at how your eye actually operates in these conditions. 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 comprises cone cells and rod cells, named for their respective shapes. The rod cells are able to function even in low light conditions. They are absent from the fovea. As you may know, the details and colors we see are sensed by cone cells, and rod cells let us see black and white, and are light sensitive and detect movement.

Let's put this all together. Imagine you're trying to see something in the dark, like a distant star in the night sky, it's much more efficient to try to look at it with your peripheral vision. By looking to the side, you use the rods, which work better in the dark.

The pupils also dilate in low light. It takes less than a minute for the pupil to fully dilate but it takes about 30-45 minutes for your vision to fully adapt and, as you've experienced, during this time, your ability to see in the dark will increase greatly.

Here's an example of dark adaptation: when you walk into a darkened cinema from a well-lit lobby and have a hard time finding a seat. After a while, your eyes get used to the situation and before you know it, you can see. This same thing occurs when you're looking at stars at night. Initially, you won't see many. If you keep looking, your eyes will dark adapt and the stars will gradually appear. Even though your eyes require several moments to begin to see in the dark, you will immediately be able to re-adapt to 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 many people don't like to drive at night. If you look directly at the ''brights'' of opposing traffic, you may find yourself momentarily unable to see, until that car passes and your eyes once again adjust to the night light. To prevent this, don't look directly at headlights, and instead, try to allow peripheral vision to guide you.

If you find it increasingly difficult to see at night or in the dark, book a consultation with our doctors who will explore the reasons this might be happening, and rule out other and perhaps more serious causes for worsening vision, like cataracts and macular degeneration.

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