Can humans see in the dark? The answer is yes and no. Yes, according to a 2013 study, at least 50 percent of the human population may be able to discern the movement of their own hand in absolute darkness. That revelation might help people feel more comfortable in the dark, but most amateur astronomers aren’t trying to see their hand waving in the dark. They are trying to see a faint, fuzzy object in a dimly lit environment. Also, when one is under the stars, there is no absolute darkness. No, we don’t see as well in the dark as many nocturnal animals, but we do see much better in “relative darkness” than most of us imagine.
Newcomers to dark skies have a hard time trusting that they can find their way from place to place or move a chair or find an eyepiece without a flashlight. Believe it or not, if you practice a few tips, you can see (or perceive) better in dim light than you can with a bright flashlight or in a city nightscape. Except for sometimes putting my eyepieces back into the case and reading a star chart, I NEVER use a flashlight when I am at a star party. Even with my astigmatisms and cataracts, I still NEVER use a flashlight to get around when the stars are out. How is that possible?
Our eyes have rods and cones. Both rods and cones contain photopigments that are light-sensitive chemicals. Light exposure causes these photopigments to undergo a chemical reaction that converts light energy to electrical impulses interpreted by the brain. Rhodopsin is the photopigment used by the rods to enable vision in low light conditions. Bright light causes these pigments to decompose, thus 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. This is described as “night vision.”
Our eyes adapt faster to bright light than they adjust to darkness. Cones attain maximum sensitivity in five to seven minutes, while rods require 30 to 45 minutes or more of absolute darkness to attain 80% dark adaptation. Total dark adaptation can take many hours. While the rods in your eyes are far more light-sensitive than the cones, they can only discriminate between black and white and provide low-quality images by contrasting the available light source behind objects. (See coopervision.com/blog/how-eyes-see-night)
You can now see why it’s nearly as detrimental to be blasted by someone’s flashlight, cell phone, electronic tablet, or computer screen as it is to your own lighting. That fuzzy object that you were viewing might dip below the horizon by the time your night vision recuperates. Based on an understanding of how night vision works, the number one tip to apply is AVOID COMING INTO VISUAL CONTACT WITH BRIGHT LIGHT. This includes super bright, red LED lights. Other tips to maintaining or improving your night vision include:
- Wear sunglasses. Aviators use this trick before flying at night. A few hours of bright sun can add 10 minutes to the time it takes for dark adaptation. Several days of bright sun can further reduce night vision. Gray or red tinted lenses are best. Wear sunglasses regularly and at least 20-30 minutes before venturing in the dark.
- Let your eyes adjust naturally. Close your eyes and cover them for a while before heading out into the dark. Amazingly, using light pressure with your palms on your eyes can help speed up the adjustment process.
- Wear an eye mask. If you are inside a room with some light and walk outside into the dark you are very likely to stumble. If you wear a mask for a few minutes beforehand, you will confidently find your way at night.
- Dim your illuminated equipment as low as possible. This helps activate rhodopsin and allows your eyes to adjust to the dark.
- Look for outdoor silhouettes. Since rods don’t register color, make the best use of black and white contrast while navigating the dark. Peruse the environment around your observing site before nightfall. Trees, mountains, and structures all provide outlines or silhouettes that contrast against a night sky. Mental notes like “turn left at the structure that looks like a goal post and walk between the pair of trees to stay on the path” allow me to avoid using a flashlight.
- Quit smoking. You can now add one more reason to your list to quit smoking. Nicotine can cause your eye to stop producing rhodopsin, the pigment essential for night vision.
- Take Vitamin A supplements. While taking extra Vitamin A will not improve night vision, preventing Vitamin A deficiency may avoid night blindness.
It is said that as blind people rely on other senses, those senses become heightened in the process. As you allow your eyes to serve you as they were intended, and as you use your sense of touch to memorize the feel of each eyepiece in your hand, the size of your favorite observing books, etc., the more and more you will find yourself less reliant on artificial light. The more of us that trust our ability to “see” in dim light, the less light pollution we will have in our environment and the better we will all be at finding those faint fuzzies.