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How Eyes See at Night

If you know how our eyes work, you know they need light to see. So how do we see so well in almost complete darkness? Our eyes let us see an incredibly wide range of lighting conditions due to different parts of the eye working together. Read on to learn how our eyes see at night and how to improve your night vision.

How do we see in the dark?

Our vision range in varying light conditions comes from three parts of the eye:

The Pupil: The eye in many ways is like a camera. The camera’s aperture is the part that expands and contracts to let in more or less light. The pupil works in a similar fashion. It will get very small in bright light to physically block the amount of light reaching the retina and will open wide in the darkness.

Rod and Cone Cells: Our eyes use two different types of cells to see light: rods and cones. The cone cells perceive fine detail and color but need bright light in order to do so. Rod cells can only see black and white and have poor resolution, but remain sensitive even in very low light. A white barely seen by the rods must be increased in brightness 1,000 times before the cones can pick it up.

Photopigments: Both rods and cones contain light-sensitive chemicals called photopigments. When exposed to light, photopigments go through a chemical reaction that converts light energy to the electrical activity our brains know how to interpret. Rhodopsin is the photopigment used by the rods and is the key to night vision. Intense light causes these pigments to decompose reducing sensitivity to dim light. Darkness causes the molecules to regenerate in a process called “ dark adaptation” in which the eye adjusts to see in the low lighting conditions.

Preparing your eyes to see in the dark

It’s much faster for our eyes to adapt to bright light than to adjust for the darkness. Cones attain maximum sensitivity in five to seven minutes while rods require thirty to forty-five minutes or more of absolute darkness to attain 80% dark adaptation. Total dark adaptation can take many hours. If you’d like to speed up the process, here’s a few tips:

  • Wear sunglasses. A few hours of exposure to bright sunlight can reduce your ability to adjust to the darkness by 10 minutes and 10 days of exposure can cause a 50% loss of night vision. Be sure to wear glasses with a grey tint to block out the entire visible spectrum and the darker the lenses the better. Wearing red-tinted glasses for 20-30 minutes before going into low light will help as well since rod cells don’t pick up the color red. This is a trick aviators use before night flying.

  • Lower the brightness on your computer screen. By keeping the brightness on your computer or TV low, your eyes won’t have to adjust as much.

  • Avoid looking directly at bright lights. Looking directly at a bright light can greatly increase the amount of time your eyes need to adjust to the darkness. If you must look towards a light, try closing one eye to maintain some dark adaptation. When driving at night, try not to look directly at high beams coming towards you and look to the lines in the road to stay on course.

  • Let your eyes adjust naturally. Before going into a dark area and risking bumping into something, close your eyes and cover them for a while to let them adapt. Also, applying slight pressure with your palms can help speed up the adjustment process.

Being able to see well at night is important for both your convenience and your safety. To help preserve your night vision, be sure to get enough vitamin A, avoid smoking, and wear sunglasses when outside.

This post originally appeared on Cooper Vision.

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