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Turn Out the Lights: How Does Night Vision Work?

Sometimes you get ready for bed and turn off the light, but you can't sleep. You open your eyes and you can't see a thing. It takes a few minutes for your vision to return. This process is known as ''dark adaptation'' and it helps our eyes get used to low light settings.

Night vision involves a number of 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 rod-shaped and cone-shaped cells. The rod cells have the capacity to function more efficiently than cone cells in low light conditions. Those cells are not found in the fovea. You might already be aware that the cones help us perceive color and detail, while rod cells 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, like the edge of the last stair in a dark basement, you'll be better off if you view it with your peripheral vision. If, on the other hand, you focus on the object itself, you'll use the fovea, which is made up of cone cells that are less responsive in low light conditions.

Another method by which your eye responds to the dark is by your pupils dilating. It requires approximately one minute for the pupil to completely dilate but it takes about 30 minutes for the eyes to achieve full light sensitivity. During this time, your eyes become 10,000 times more sensitive to light.

Dark adaptation occurs when you enter a dark cinema from a bright lobby and have trouble finding somewhere to sit. But soon enough, 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. At the beginning, you probably won't be able to actually see that many. Keep looking; as your eyes continue to dark adapt, the stars will become easier to see. Even though you need a few noticeable moments to adapt to the dark, you'll quickly be able to re-adapt to exposure to bright light, and this resets any dark adaptation that had developed where it was darker.

This explains one reason behind why many people have difficulty driving their cars at night. If you look right at the lights of an approaching car, you are momentarily unable to see, until you pass them and your eyes readjust to the night light. To prevent this, try not to look right at the car's lights, and learn to use your peripheral vision to observe oncoming traffic at night.

There are several things that could, hypothetically cause trouble with night vision, including: a nutritional deficiency, macular degeneration, cataracts, glaucoma, and others. Should you begin to suspect difficulty with night vision, book an appointment with one of our eye doctors who will be able to shed some light on why this is happening.


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updated Feb. 16, 2023
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