‘Night Vision’ of the human eye is an interesting phenomenon.
The dynamic range of our eyes is remarkable. The eye can adapt to an extremely wide range of light (brightness) conditions from very bright to extreme low light conditions.
Human Night Vision Facts & Tips
The eye automatically adjusts to changes in brightness. Remarkably the human eye can function effectively within an extreme range in brightness from very bright to very dim. I have read that this dynamic range is “well over 1,000,000:1” !
There are two primary mechanisms (receptors) in the eye’s retina. They collect and send light impulses to the brain. Rods and Cones.
Without going into lots of technical detail, the basics are this:
Rods are receptive to brightness (intensity of light).
Cones are sensitive for color perception and visual acuity (focus).
While both Rods and Cones in the eye function throughout a very wide range of illumination, below the intensity of moonlight the Cones cease to function.
The dimmest light in which the Cones will somewhat effectively function is similar to 50% moonlight. The Rods can ‘see’ all the way down to an overcast night with no moonlight. Though with greatly reduced focus and color perception due to the Cone’s inability to function well in extreme low light.
Night Vision Adaptation Of The Eye
Rods and Cones differ greatly in their rate of dark adaptation. (That’s the speed at which they adapt to changing illumination conditions).
Rods (the receptors for greatest night vision) require 45 minutes or longer of absolute darkness to attain maximum sensitivity after exposure to bright light.
The Cones do not achieve the same level of night vision sensitivity as the Rods. The Rods slowly adapt to dim illumination, but eventually achieve a much greater sensitivity than the cones.
Dark adaptation (Night Vision) is about 80% complete within 30 minutes. But it may take hours, or even days, to acquire total dark adaptation.
Human Night Vision ‘Blind Spot’
The center of the eye’s visual feed is loaded with Cones. The center is completely absent of Rods. Therefore if the ambient light is below the Cone threshold (approx. 50% moonlight), a blind spot will present itself in the central field of vision.
The Rods reach a maximum concentration at a peripheral around 17 degrees of your central vision.
How To See In The Dark | Natural Human Night Vision
While attempting to ‘see’ in low ambient light dimmer than moonlight (relying solely on your eye’s Rods to ‘see’)
Look approximately 15-20 degrees to one side, above, or below the target in order to place the target on the part of the retina that has the highest density of Rods.
You can also fixate to one side of a target to avoid the central blind spot, as well as to scan, utilizing the most sensitive part of the retina to improve target detection at night.
Poor Color Sensitivity When It’s Dark
Rods and Cones have different sensitivities to visible wavelengths of light (colors).
Color vision is lost under very low light conditions. (The Cones “don’t work”).
Rods are mostly sensitive to blue – green while less sensitive to the red portion of the visible spectrum. In other words while using human night vision, if looking off-angle at a target (15-20 degrees), Green will appear brighter than the Red.
Best Color Light For Night Vision Retention
It’s best to use a dim Red light at night to retain your natural human night vision. Some flashlights and headlamps integrate with adaptable red filters or separate red LED.
THE most popular (and cost effective) Headlamp (with red light included),
Foxelli Headlamp Flashlight
(potential amzn commission at no extra cost to you)
Related: Headlamp vs Flashlight
Visual Acuity (Focus) At Night
Your eye’s ‘focus’ or visual acuity under low light conditions is not good. Focus is reduced at night under low illumination. 20/20 vision cannot be sustained below a level of deep twilight. Vision may be reduced to 20/200 or less.
Visual acuity at night is derived from small differences in brightness between objects and their background (contrast).
Flash Blindness
Dark adaptation of the Rods develop slowly over a period of 20 to 30 minutes to approximately 80% ‘night vision’.
However human night vision can be lost in a few seconds of exposure to bright light.
Dark adaptation is independent in each eye. Even though bright light may shine into one eye, the other eye will retain its dark adaptation if it is protected from the light.
You can prevent flash blindness and preserve dark adaptation in one eye by simply closing or covering it. For example, if you must momentarily turn on a flashlight, you might close one eye first to retain your night vision.
Real Night Vision Devices
Speaking of night vision, I can’t help but plug Bob over at ‘Ready Made Resources’ who has the best prices on night vision devices anywhere. Although a significant investment, a Night Vision Device is a tremendous force multiplier (and has many additional uses).
Here is his lineup of NVD’s:
The Best Prices on Night Vision Devices Anywhere
Continue reading: Night Vision Devices Critical for Nighttime Security
Interesting read. It brought back memories. Two kinds of flashlights in common use when I was in the Army. The angle kind and the old straight ones. My preference was for the straight one as I could hold it in my mouth and point it while working on wounded. Back to enemy to try and shield the light. Constant prayer going, “Please God don’t let anyone shoot the light!” We used red lights on the boat when we were cruising and they were great. Anyone considering having to go out into the night should try and stay in a room with red lights for half an hour before doing so. Of course this is not always an option. On my night stand I keep one of the newer multi function flashlights. It has high, medium, low, strobe and SOS capability. I have it set to come on as a strobe as it will blind an intruder for several seconds. I’m very impressed with this flashlight and I’m sure they are available on Amazon. I use lithium batteries in mine’ On the NVDs I had a cheap Russian made level 1 from K-mart 20 years ago. It was total garbage. It… Read more »
Meant to add, we used the red lens in the flashlights in Vietnam.
What a relief! Thanks, Ken. Thought I was losing my sight when I tried to focus directly on a star at night only to have it disappear when I looked directly at it.
Lived in West Africa for a while on the coast about the middle of the big bulge. We were amazed that we could read by starlight and see colors in the moonlight. Never figured it out but must have been some combination of darkness, clear air, and proximity to the water. One of the coolest aspects of that assignment.
– Night vision is something the Army spent a lot of time on, making sure we knew how to use it and teach others how to use. It is absolutely true that visual acuity goes down at night; it’s also true that there is a blind spot where you normally focus. I have literally been able to overlook an M60a1 tank that was parked right in front of me by having it in that blind spot. You have to keep your eyes moving, your head on a swivel and not looking at the center but the edges of your vision. People are still amazed at what I can see at night, when they can’t see it because they don’t know how to look. I do remember a story of one of the GI’s in an FOB in Vietnam who served as a sniper watching the wire at night. According to legend, he would not come out of his hooch at all during daylight to preserve his night vision, and reportedly wore dark sunglasses at night when flashlights might be in use. It might be a bit extreme, but it kept his unit’s morale up and sappers out of the wire.… Read more »
Me again, one way to keep your eyes healthy is to eat properly and use bilberry supplements. Look up bilberry it is an European blueberry basically. In WWII the pilots noticed they could see better on night runs if they ate bilberries. The retina benefits from good vitamins. I have been using bilberry for several years now and it helps. I use Solaray One Daily, best price at Vitacost that I know of.
Another possibility (possibility only, as different people react more or less) is yarrow. It CAN help with night sight. It can also make your eyes extremely sensitive to sunlight, so use with caution.
Same family as carrots, celery, queen annes lace, parsnip,,, ?
Latin name Achillea millefolium, plant family asteraceae. The others are Apiaceae or Umbelliferae, so not the same family.
Just for fun look up why some old war fighters wore an eye patch .
secondreon; There was a “Mythbusters” episode about pirate eye patches . In the episode, they tested switching eye patch sides when going below deck on a ship raiding adventure. If my memory serves me correctly (sometimes it does), they completed the obstacle course much better using the one eye not exposed to light, rather than stumbling around using two eyes fresh out of the daylight
If you are going to try night vision optics I would recommend going with digital over tubes. Much less expensive and getter better everyday. I have a digital NV scope that with the illumination is a good as gen III that cost 4x the price. Works great on varmints at night under 200 yards. You can clearly see the difference between hogs , deer and cattle.
+1 on that one,
Theres added benefits too such as recording the shot if its on a rifle, and the one i have is day/night so can zero and it holds across the board, the one i have also has range finder, have checked it against my Vortex and dope card and is pretty right on, is dependent on how good your input was though,,,,
I know the same company makes spotting scopes as well as monoculars with the same digital platform
I have an excellent flashlight, that looks like one of those tactical flashlights, and it’s made by Bushnell. It incorporates a brilliant white light, push the button and you have the red light, or push the button again and you have a “blood” light, which is sort of purple, and makes a blood trail stand out sort of florescent at night. I always carry it when hunting, or doing other activities in the woods and back country. Very nice light and not too big. You can carry it easily. I also seem to see quite good at night without a light to. It must be all those carrots I eat from my garden. 🙂
P.S. Very good article to read. Thanks for the info Ken.
Navigating the woods (dark alleys or buildings searching for burglars, when a cop) is something I did often. Everything Ken spoke of helps. Practice helps more, as it helps you learn how to move, especially your feet, searching for contact with obstacles before tripping or otherwise compromising your balance. My next tip is a two edged sword. Eye protection, if navigating through the woods in the dark. If stealth is the reason for limiting lights, amplified hearing helps. I use “Walker Game Ears” both when shooting on my range, and at night when engaging marauding varmints. This does two things, it reminds you how much noise you yourself are making, and alerts you to movement being made by your quarry. My third tip, while it may sound as contrary to wearing eye protection, has some advantages. I have found that, as I age, I’ve become more farsighted, I wear tri-focal corrective lenses. I’ve found that I can actually see better in very low light conditions w/o my glasses. I’m not reading a book, I’m trying to locate that “bump in the night” while still being capable of engaging if I must. I practice instinct shooting continually. I never use sights… Read more »
I didn’t know the science behind it, but I figured out how to do exactly what you described when I was kid and we would play man hunt in the dark on our 3 acres.
🙂 Very cool!
My grandfather spent the last 20 years of his life with macular degeneration. It didn’t stop him from reading. He just learned to read from the sides of his vision.
The night vision blind spot explains a lot. Here I thought I was just starting to go blind, that’s another reason I tend to walk around in the dark. I figure I had better get used to it. Well that’s a relief.
Practicing SHTF skills today….running on generator due to major power failure in area from winter storm. 14 inches and still snowing. Absolutely BEAUTIFUL. DH says he has never met anyone so energized by snow and an emergency as me! LOL. Going out to feed livestock. New calf born yesterday and another on the way. TTYL.
Good article Ken and I agree with Dennis in his observations. I would like to add:
Some of the ammo manufacturers are creating standard pressure “low flash” loads for handguns. After my last shooting as an LEO. ( which took place at night in a Metro Area.) I became interested in these low flash loads myself
As a result, I have reloaded most of my ammo using small amounts of fast burning powder that creates less residue as an added benefit. Examples of such powders include Titegroup or Bullseye which will launch the projectile at adequate speed, clean burning and low flash when fired in a darkened area. The “cleaner burning” the powder, generally equals a load with less flash. Dennis, I know you did not like the way Titegroup scorched your brass. The faster burning powders tend to scorch brass but it burns almost 100% within the chamber and barrel. ( resulting in less muzzle flash.)
Many thanks go to those range owners that allowed me on their facilities to test different loads after hours when we had free range to turn out the lights.
CaliRefugee/Dennis
Question,
Flash supressors? I know one of my ARs have one, will it suppress the flash?
I know the rest with competition brakes will blind me, just know this from reading, but am curious about muzzle devices that are considered flash suppressors
Tommyboy, Don’t have much knowledge on flash suppressors that’s not on the internet. They re-direct the gasses as the exit the barrel, directing them to the sides, out of the sight picture. They don’t “hide” the flash or make it disappear, but make it more of a round ball as opposed to a long stream. It reduces the flame some by dissipating the gasses more quickly. Since I only use rimfire rifles or .410 shotgun after dark for critter control, muzzle flash is not a problem for me. I use standard pressure loads in my “bump in the night” handguns so I can carry a flashlight in one hand. I have weapon mounted lights on my critter stoppers. A high intensity light mounted inline with the sight picture will mitigate the effects of the minimal muzzle flash of those two particular weapons, each of which I choose according to the critter I’m going after at the time. I don’t shoot high powered rifles after dark, but that’s just me. Too many things to consider, safety wise, due to limited distance of visibility of background outside, and way to much penetration inside the house. Again, that’s my self imposed restrictions, not… Read more »
I think of the Great Whit shark thing. Californian made it illegal to fish for Great Whites however fisherman are completely legal as prey for the sharks. Yet we can’t act in self defense when they are around.
We here in the peoples republic of the not so great state of California now have to remove the flash hiders from our weapons. Also no more adjustable or folding stocks, No pistol grips or thumbhole stocks, nor fore end pistolgrips and no more removable magazines. Sucks to be me but if I moved I’d lose half of my preps and paid for house. In 3 days I’ll be 69 and I’m getting to old to start over.
Point being I’m tired of the PTB regulating my ability to protect my self against criminals who due to their lack of respect for ROL can out gun me.
Me;
I would first state I don’t believe in doing things illegal, or advocate doing so.
BUT, when is the last time a “Brown Shirt” crashed into your home and searched for a “thumbhole stock” or any of the other items you listed?
And I’m wondering how those speed-limit signs are doing for keeping people from breaking the speed limit….stupid laws?
There is a quote I believe it goes something like this “It is better to be judge by 12, than carried by 6”.
So the questions are you going to drive 56 MPH to safeguard you and your family? You stated you’re soon to be 69, and too old to “start over”.
Respectively Sir, if neither is an option, than you’ve run yourself out of options.
To me:
For a few years after I left LEO work, I did get some private security gigs. As a civilian, I was not allowed to be armed like I was when I was a cop.
I also had the experience of actual gunfights and so in high risk transport jobs, I carried multiple working weapons on me for the “New York Reload”. Many older cops have willed or left me their old backup pistols over the years so I still have a good collection of small hide-out weapons. I had a part time job at a local gunship learning how to clean and replace springs and parts in these old guns. I kept the pick the litter for myself.
They are no good at taking deer butt they come in mighty handy when the attack comes fast and close enough to smell the body odor and bad breath. My wife is still bothered by the sheer number of working weapons stashed around the house to this day.
Ask yourself, do you ever put down home invasion or skunk in the hen house in your dsayplanner?
Oops! typo alert: I never worked at a gunship. I meant to say Gun Shop.
and, contrary to popular thought, I did not step out of George Clinton’s Mothership. ( reference to “Parliament” – the funk group..)
NRP. Cali, Thanks for your thoughts. As I am pretty much a ROL type guy I try not to break too many of them. Although I’m now being mandated to do this stuff I’m not being required to get rid of the parts. Reinstalling should only take a couple of minutes. I do have other things that go boom for the things that go bump in the night.
me;
I have researched and heard that in Crapaforina if you pull the two pins on those AR’s breaking them into the two main parts they are no longer considered a “working firearm” regardless of the makeup of parts on those “two parts”.
This includes the fact that the AR still does NOT have that stupid Mag Locking device required….. or Bump Stock or Thumb Hole or Front Vertical Grip or etc. etc. etc.
That would probably be true but I wouldn’t want to be one that put it to the test. If DW decided that she no longer wanted to be DW a call to the local brown shirt office could be problematic. At the least it could be no big deal. On the other end of the spectrum it could turn into a very expensive problem.