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Turn Out the Lights: How Does Night Vision Work?



Some nights, you lie in your bed, all ready to dream the night away with the lights off, but you can't fall asleep. You open your eyes and you can barely make out a thing. It takes a few minutes for your eyes to adjust to the dark. This remarkable process is ''dark adaptation'' and it lets our eyes adjust to low light settings.

In order for night vision and dark adaptation to be successful, many physiological, neurological and biochemical mechanisms have to take place behind the scenes. So how does it really work? Let's examine the eye and its anatomy. The retina is a layer of cells at the back of the eye. The portion of the retina behind the pupil that is responsible for sharp focused vision is called the fovea. The retina comprises cone cells and rod cells, named for their respective shapes. The rods are able to function even in low light conditions but those cells are not found in the fovea. You may have learned that the details and colors we see are detected by the cones, and the rods are sensitive to light and detect movement.

Considering these facts, if you want to see something in the dark, like a faint star in the night sky, instead of focusing right on it, try to use your peripheral vision. When you do that, you use the part of the eye that has rods, which, as mentioned above, are more responsive to light, even if there isn't much of it.

Another mechanism your eye implements to adjust to low light is pupil dilation. Your pupil reaches its maximum size in less than a minute; however, your eyes will get better at seeing in the dark over a half hour period.

You'll experience dark adaptation when you walk into a darkened cinema from a well-lit area and have trouble finding somewhere to sit. But after a couple of minutes, your eyes get used to the dark and see better. You'll experience a very similar phenomenon when you're looking at stars at night. At first you won't see many. If you keep gazing, your eyes will dark adapt and millions of stars will become easier to see. It'll always require a few moments until your eyes fully adjust to regular indoor light, but if you walk back out into the brightness, those changes will vanish in a flash.

This explains one reason behind why many people have trouble driving at night. When you look 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, don't look directly at headlights, and learn to use peripheral vision in those situations.

There are several things that can cause difficulty seeing in the dark. These include diet-related vitamin deficiencies, macular degeneration, cataracts, glaucoma, and others. Should you begin to detect that you have difficulty seeing in the dark, call to make an appointment with one of our eye doctors who will be able to identify and rectify it.