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Biological Night Vision, or Scotopic Vision (your vision under low-light conditions,) is a topic that has a wide array of information out there. What I’d like to do in this article is not only attempt to clear up some misconceptions of what aids in better biological night vision, but offer some methods of preserving your night vision.
Parts of an Eye
Without turning this into an anatomy lesson, your eye has rods and cones, which are examples of photoreceptors (neurons) found in the retina that convert light into electrical signals. These electrical signals travel to the brain through the optic nerve and are used by your visual system to form a representation of the world. In other words, this is your sight.
Cones are active in higher light-levels (photopic vision), are non-functional in low-light and create our color vision. They also provide our highly developed spacial acuity. Rods are responsible for your vision in low-light conditions (scotopic vision.) While higher in number than Cones 120 million vs. 6 million,) they’re more sensitive, but not to color.
Within your rods lies Rhodopsin, the chemical that actually allows night vision. When exposed to light, Rhodopsin bleaches and takes around 30 minutes to regenerate. Despite taking so long to regenerate, most night vision returns within about 5-10 minutes once the bleaching (or being exposed to bright light) occurs.
If you’re wondering what gives animals their increased night vision, look no further than the Tapetum Lucidum, which we humans unfortunately do not have. It’s a tissue layer found at the back of animal’s eyes which reflects light back through the retina, increasing the available light available to capture. This is why animals have “eye shine” when you light them up at night with a flashlight. The Tapetum Lucidum is found in many nocturnal animals and even some deep-sea animals. It’s claimed that animals night vision is equivalent to a 1st or 2nd Generation Night Vision Intensifier Tube.
What Helps Retain Night Vision?
The first thing I’d like to mention is different spectrums of light to prevent that immediate bleaching of Rhodopsin and the loss of your night vision.
The Rhodopsin contained within the rods in your eyes are less sensitive to the color red within longer wavelengths of light. You may have seen the Military using red light to read maps and preserve their night vision. Although, there has been a shift recently to using green light or a blue-green light instead of red.
Green allows for more visual acuity and better differentiation between colors, but this is of course at low-light levels. Both red and green light at high output will kill your night vision, no matter what color, so keep that in mind. Whatever color you feel helps you more, try to use the least amount possible. If you’d like more information on the green vs. red debate, here’s a great article written by Astronomer Doug Kniffen.
I’ll also add that uses of low-light in the red, green or blue-green spectrums aren’t limited to the Military. If you’re doing anything outdoors at night, high-output white light will kill your night vision faster than anything and you’ll benefit from a different spectrum, provided it’s low-light. There’s a lot to learn about lighting when it comes to using it at night, or in combination with Night Vision Image Intensifiers, but I’ll save that for a future discussion.
A Quick Shut Down
Something that you can use as a field expedient method to quickly adjust your eyes to a dark environment, when moving from a light one, is to close your eyes and count to ten. This may sound trivial, but it does work. It won’t dramatically bring you to the level that increased time will, but it’s better than quickly getting hit with a dark environment.
I can’t take credit for this method at all and it’s actually something that stuck with me from my childhood. I read every book about Detectives I could get my hands on growing up and an illustrated Detective’s Handbook from the 80’s (that I still happen to have) is where I learned about the method I’ve described.
I’d have written it off if it didn’t work, but it does. Give it a try sometime.
Now we come to the most historically debated method of retaining your night vision, eye patches. I say “most debated” because of the lore surrounding Pirates using Eye Patches to aid them in adjusting to darkness when moving below the deck of a ship. There was typically no light below deck other than ambient light and these sailors would need to quickly adjust during battle, etc.
The TV Show Mythbusters actually tested this and deemed it “Plausible,” here’s the description of their testing:
“This myth works under the assumption that the eye covered with the eyepatch is already accustomed to low light conditions, while the other eye must take time to accustom. The Mythbusters were sent into a dark room with light-accustomed eyes and were told to complete certain objectives. Their movements were hampered by the darkness and it took them five minutes to finish. When they went into a rearranged but equally dark room with an eye that was covered for thirty minutes, the Mythbusters were able to complete the test in a fraction of the time. As a control test, the Mythbusters then went back into the same exact room with light-accustomed eyes and ran into the same difficulty as the first test. The myth was deemed plausible because there is no recorded historical precedent for this myth.”
I wasn’t able to track down much information around pirates and their reasons for eye patches other than the obvious one of an injury and that One-Eyed Willie had one in the movie Goonies. Something interesting I did find was that the FAA recommends that pilots close one eye to preserve night vision. “Since any degree of dark adaptation is lost within a few seconds of viewing a bright light, a pilot should close one eye when using a light to preserve some degree of night vision.”
Hopefully you’re now better armed with some knowledge of what your eyes do in the dark and a few ways to preserve your night vision.
Are there other methods you’ve head about? Share them below in the comments.
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I also heard somewhere that when using your night vision, to look out of your peripheral vision. It supposedly has stronger focus in the dark. Don't have enough experience with night vision to confirm if this is true or not. Just something I heard.
Adaptation to darkness works better when you use red shaded glasses while in a bright environment. This is based on the Purkinje effect (http://en.wikipedia.org/wiki/Purkinje_effect). This happened to be a question on my first state examination to become a doctor.
Regarding the eye patch--I once read folks who sailed in those days used the sextant for navigational purposes. The sun caused blindness in many cases, hence the patch. Not being conversant with the sextant or it's use, I do not know.
as tacky as it is, rose colored shades, or wear your sunglasses at night. it softens the change and when you go from high light to low light it leaves an area of contrast from your peripheral vision (where you can't see anything) to the center of your eye where you can see much better. that contrast can help you discern differences in what you can and cannot really see helping you sort things out. not as effective as an eye patch but it's much less ridiculous looking. also, a hat or keeping your eyes in the shade cuts the wait time for adjustment significantly.
It is said that pirates wore gold ear rings because in that ear position (middle of the ear lobe) it is the EYE ear acupuncture point, which improves eye performance.
Look for ear acupuncture charts in the internet and you will see it is right!
As a child I had to wear an eye patch for a week or so. I discovered that in total darkness when I lifted the eye patch I could see clearly. That is too dark to see my hand in front of my face and with the eye that was covered by the eye patch I could read the headlines on a newspaper and see obstacles clearly.
I have used the one eye closed method. Akin to the eye patch without having to say arrrr. I would say it is very effective in my own experience.
I few additional tips I learned. Close your dominant eye the one you use for sight picture and alignment.
Low level red light helps you stay operational while your eyes adjust.
This method does not work for flash bangs as the searing white hot light goes right through the eyelid. But it does work well for trip flares and sudden light shock like headlights or spotlights.
As a retired submarine officer, I can tell you the eye patch solution works but, with a minor loss of depth perception because you are looking through only one eye (need two eyes for good depth perception). In many submarine movies you see officers at night wearing red lens glasses or goggles. While, promoting night vision, red lenses have a short coming. Anything in red cannot be seen, since the red wave lengths blank out anything in red. This means that you cannot see out of specification readings which are written and circled in red, your red soundings and other critical features on charts cannot be seen, and you cannot differentiate wires, leads, valves, or signs in red, unless you remove the red goggles or glasses-- which when removed ruins your night vision. Since submarine OODs have to night vision adapted between nautical sunset and nautical sunrise I wore an eye patch. This allowed me to see everything in normal light-- including items in red--while maintaining night vision in the other eye. If the sub had to come Periscope Depth (PD) you could maintain your night vision in the patch covered eye until the control room was rigged for black and you were ready to put that single eye to the raised periscope eye piece. You see when " dancing with mother Kollmorgen" you only need to use one night adapted eye.
For non-boat sailors: mother Kollmorgen is another name for the periscope which was manufactured by Kollmorgen. Dancing with Kollmorgen is based on how sometimes you looked with your arms around the periscope manipulating it--it sort of looked like how you would your mother or grandmother if you were dancing with them in public.
@dustinacox You're completely right, we've evolved for having clear definition during the day so at your focal point the concentration of cone cells is very high leaving no room for the rod cells used in night vision. But to practically apply this, you'll want to look near the object you wish to see, not out of your peripheral. Try to focus on something the same distance away and just near it. Then without moving your eyes shift your mental focus to explore whats nearby. If you practice regularly it becomes like second nature when you need to see at night.