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Night Vision

Everyone has found themselves in the dark, 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. Gradually, the things in the room begin take shape. This process, ”dark adaptation,” allows our eyes to adjust to the dark.

Many people don’t know that night vision relies on the cooperation of physical, neural and biochemical mechanisms. So how does this work? The human eye contains photoreceptors that can be classified as rod cells and cone cells, which are found at the back of the eye; or, to be precise, on the retina. Together they make up the sensory layer that gives your eye the ability to see colors and light. The rod and cone cells are spread throughout the retina, with the exception of the small area known as the fovea. The fovea is made up of only cone cells, and its main function involves creating a focused image. What’s the functional difference between these two cell types? Basically, cones contribute to color vision, 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, like the edge of the last stair in a dark basement, it’s much more efficient to look at 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.

Another way your eye responds to the dark is by your pupils dilating. The pupil reaches its biggest capacity in less than a minute but it takes about 30-45 minutes for the eyes to achieve full light sensitivity. During this time, your ability to see increases by a factor of 10,000 or more.

Here’s an example of dark adaptation: when you enter a dark cinema from a bright area and have a hard time finding a seat. But soon enough, you get used to the dark 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. Keep looking; while you dark adapt, the stars will become visible. Even though you need a few noticeable moments to adapt to the darker conditions, you’ll quickly 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 one reason behind why a lot people prefer not to drive when it’s dark. When you look right at the lights of a car heading toward you, you are briefly unable to see, until that car passes and you readjust to the night light. To prevent this, try not to look right at headlights, and instead, use your peripheral vision to observe oncoming traffic at night.

If you’re finding it challenging to see when it’s dark, call us to schedule a consultation with our doctors who will be able to look into why this is happening, and eliminate other and perhaps more serious causes for poor night vision, like cataracts and macular degeneration.

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