‘Night vision’ of the human eye is an interesting phenomenon – a sensation, a uniqueness that many do not experience in today’s modern (bright) world. There are times though when our human night vision if properly adapted, could become a powerful nighttime asset, and with regards to survival & preparedness, this might be one’s own security (for example).
Our eyes are a remarkable thing in how well they can adapt over an extremely wide range of light (brightness) conditions.
Here are a few facts and tips regarding your human ‘night vision’ while using your own unassisted eyes…
As the sensitivity of the eye automatically adjusts to changes in illumination, the human eye can function effectively to changes in brightness as much as 1,000,000,000 times! More importantly (with regards to ‘night vision’) there are two primary mechanisms (receptors) in your eye which collect and send light impulses to the brain. Rods and Cones.
Without going into lots of peripheral technical detail, the thing to know is that this dual-receptor system (rods and cones) each have their own attributes for ‘seeing’ or collecting light…
Rods are used during night vision.
Cones are primarily useful for day vision, visual acuity (focus), and color perception.
While both rods and cones function throughout a wide range of illumination, below the intensity of moonlight the cones cease to function. The dimmest light in which the cones can somewhat effectively function is similar to 50% moonlight, while the rods can ‘see’ all the way down to an overcast night with no moonlight (with greatly reduced focus and color perception).
Dark Adaptation Of The Eye
Rods and cones differ greatly in their rate of dark adaptation.
Rods (the receptors for greatest night vision) require 30-45 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 is about 80% complete within 30 minutes, but it may take hours, or even days, to acquire total dark adaptation.
Blind Spot Of The Eye During Night Vision
The center of the eye’s visual feed is loaded with cones, and is completely absent of rods. Therefore if the ambient light is below the cone threshold (apprx. 50% moonlight), a blind spot exists in the central field of vision.
The rods in your eyes reach a maximum concentration at a point around 17 degrees of your central vision. Therefore while attempting to ‘see’ in ambient light dimmer than moonlight (relying solely on the rods to ‘see’), to best detect small targets under such conditions you must look approximately 15-20 degrees to one side, above, or below the target to place the target on the part of the retina that possesses 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.
Color Sensitivity Of Rods
Rods and cones posses different sensitivities to visible wavelengths of light (colors).
Under very low light conditions, color vision is lost.
Rods (night vision) are mostly sensitive to blue – green while less sensitive to the red portion of the visible spectrum. In other words, during night vision, if looking off-angle at a target (15-20 degrees), green light will appear brighter than the red. Therefore, if light must be used at night (e.g. map reading) it is best to use dim red light (some flashlights integrate with adaptable red filters).
Visual Acuity (Focus) At Night
Your eye’s ‘focus’ or visual acuity, is reduced at night under low illumination and 20/20 vision cannot be sustained below a level of deep twilight. It may be reduced to 20/200 or less.
Visual acuity at night is derived from small differences in the brightness between objects and their background (contrast).
Flash Blindness
Dark adaptation of the rods develops slowly over a period of 20 to 30 minutes (apprx. 80% ‘night vision’), it 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.
Let’s hear from you –
Your own experiences or tips regarding human eye ‘night vision’ ?
3 (today) 27 (week) 80 (month)
Here’s a trick that I absolutely know from experience works. Put an eye patch over one eye and wear it all day. Do not take it off while there is any ambient light including full moon. Then, in what would be described as pitch black, remove the eye patch and you will be able to see with that eye. This effect is even stronger if you have worn the patch for more than 12 hours or a day or two. Make sure the patch doesn’t let in any light.
Another “trick” I have used is to wire a glow stick to the end of a 2′ long stick. Activate the glow stick and hold the stick by the other end with the glow stick end about a foot off the ground and 6″-12″ in front of you. In the pitch black forest the path will be very well lit and the negative effect on your night vision will be minimal. Hint: wear a brimmed or baseball hat and glasses because you won’t be able to see small branches at eye level very well.
Possibly the reason for a pirate’s eye patch. When fighting on deck they could cover one eye and when the fight progressed to below decks they could uncover the eye.
I’ve never used a patch but have closed one eye on occasion to protect it.
You can even close one eye to an oncoming vehicle while driving on a dark road. Open the eye after the vehicle passes to restore your vision quickly.
Good article for those not up to terminator standard,i was taught to see with my ears in very low light levels,the darkness can be your friend..
Good article Ken.
I have been an amateur Astronomer for many many years, doing the “red” dim light is a way of life at 2-3:00AM out 100 miles from any light source. We, the group, have even gotten to driving in the last 10 miles with red covers over the headlights. Makes an interesting store to the local cops until they figured what we were up to HAHAHAH We don’t even try to “see” before spending an hour in the dark, setting up and just talking about the “targets” for the night.
It is amazing what you can actually see even without the “red” flashlights on, and how fast you can actually get “adjusted” to no or very little light.
Even in the home, people seem to always turn on a light when walking for that “glass of water” or to get rid of that glass of water. There is enough light on at night to see perfectly fine, the blue light from the oven control, the red light from the DVD player, the small light from the Refrigerator and so on or even that little bit of moon light creeping in.
NRP
Hey NRP! Glad to meet another amateur astronomy family! We have red LED nightlights and sometimes string red LED Christmas lights when we need more light at night. Red light does not interfere with your night vision. Also, red lights do not interfere with your sleep/wake cycle (circadian rhythm), so you can get up and get that glass of water (as long as the refrigerator light doesn’t blind you) or go to the bathroom (this is where we use a red nightlight) and we’re able to get back to sleep.
Opening the Frig in the middle of the night is very very bad for me, sure screws with the diet… LOLOL
BUT, when I do hit the left over potato salad @ 2:00AM I close one eye when opening, it at least saves one eyeball to get that HUGE SCOOP of goodies. 🙂
Night fighting. If you can rob the enemy of their night vision, it is a good thing. I used a portable flash unit, held from an extended arm, straight out to the side, while the gun hand pointed down range at the “noise” of targets, moving in the pitch dark of jungle, or interior structure. Make some small noise to attract the attention of the target, then set the flash unit off, having closed your non-shooting eye. What happens is the enemy is blinded, and your open eye “captures” the field of view, like a retained photo, from the flash. The retained image will reveal the enemy positions in the hallway, or in the bush. This retained image will continue to exist after you then close your gun eye. With both eyes now closed, you point shoot according to the retained image, keeping your eyes protected from the flash of your own weapon’s discharging. Those you miss will then reveal themselves by noise, as they blindly attempt to cover. Then your ears target to the noise. Once you stop shooting, you open you eyes, looking away from the targets to move to another position, as your flash unit recharges, and you reload.
I also carry one of the world’s brightest tactical flashlights, which totally blinds an enemy, forcing them to shut their eyes, turn their heads away, and hold up a hand to block. Very useful.
Special lasers are available which do much the same thing. However, a laser spotlight will not just take your night vision, it will permanently blind a target. I call these weapons “Laser Maimers,” which can be used to stop chasing vehicles, blind an enemy emplacement, or combat line, even chase away police airborne units. They are especially nice as they are fast as light, make no sound, and leave no trace.
Had no flash bangs, no lights on pistol, no body armor, no goggles, no ear protection, no helmet, no radio, no backup, and no other team members. I wasn’t trained by anyone for this technique and it isn’t part of agency training. I worked alone in foreign lands with very limited resources. What I described is what I did. It was the best I could come up with to survive. The enemy were not professionals, nor were they military types. However, they still had guns, even if they were not expert shots. The only night combat instruction I ever received was, “just before you pull the trigger, shut your eyes.” Heck, most of the time I couldn’t have anything on me, whatsoever, least it be discovered. After all, the enemy was usually all around me, rubbing shoulders, bumming smokes.
It may not be the current fashion, but my tactics allowed me to live.
Navy big on red light. All the below deck lights on their ships go to red around 2200 hours so the night watch have night vision by the time they get topside. I had originally designed that flash technique as a pursuit evasive technique to temporary blind the pursuer and allow you time (about five to ten seconds) to plan and execute your escape plan.
When I go to bed, I turn out the lights in my kitchen to walk to my bedroom in complete darkness since I use one light at a time in the whole house. If I don’t want to spend a lot of time feeling stuff to know my location, I just grab one of my dog’s tails and follow since their vision in darkness is like dawn to them.
An interesting observation that I’ve noticed, is this…
I have several ‘night light’ plug-ins around the house which have LED bulbs instead of the typical 4-watt tungsten ‘night light’ bulbs. They are about the same brightness but use a small fraction of the power.
That said, it is quite amazing (but logical) that if and when I get up in the middle of the night to find my way to the facilities, the apparent brightness of the rooms containing the night lights appear to be substantially (lots!) brighter than when having retired for the night. This is a classic example of the eye’s night vision.
My wife has told me that my ability to see in the dark is scary and unnatural. My trick is to always keep my eyes moving in a figure 8 pattern. While walking, I continually scan in this pattern, and I can see pretty well. If I have to focus on a single point, I look off center. Ambient light helps out a lot, and it seems like the light from a fire doesn’t really hurt my night vision.
Is it just me; or does the moon seem to be setting further as you read the first few lines?
Ahhhhhhh
No Comment, LOLOL
Looking at it crossed-eyed now to see if I can get it to do so.. 🙂
hairy,the moon isn’t really there. how did the deluded idea ever get started that a big chunk of rock is just floating about in the sky? The next time you look up and think you’re seeing something like that, think about it . I mean, think seriously about it!
Ok Ok, back to the “red pill, “blue” pill thing HAHAHAHAHA
When I was younger I volunteered with a search and rescue unit in the mountains of Colorado. I quickly discovered that my night vision was much better than that of the other people with me. They couldn’t figure out why I could walk the trails without a flashlight. The trade off is that I do not see colors as well as most folks. Perhaps I have fewer cones and extra rods in my eyes? Has anyone else experienced this?
Our grandson has been diagnosed (we think??) with some color blindness. He has been given blue glasses, which he won’t wear (10 yrs old). But he has EXCELLENT night vision. He will point out birds in the trees, which we have difficulty seeing even when he points them out. He spotted a nugget of fools gold on the side of the road while riding in the car at night. While he apparently has problems reading, he had no trouble with difficult words ona TomTom GPS unit. Any help would be appreciated.
prinia
I assume you are saying parents took him for eye tests, and he was so diagnosed? One hopes the optometrist knew what he was doing, and probably does, but, on the other hand, mistakes (lack of knowledge/stupidity) do happen..Seen it happen, sigh.
so
have you sort of “checked out his abilities” yourself?
-asked him to you a ball of wool of such a color, when he has to choose it? , etc..
-ask him to read you some recipe instructions while he helps you cook?
-ask him to read to you from the newspaper (because you misplaced your reading glasses)
-ask him to read a book to a younger child/a pet/you?
etc..
don’t know much about any of this, but,
sometimes kids (or adults) will not use things such as these glasses because
-they do not actually help
-they make things worse
also, I have seen kids not complain about a condition, (in this case pain) because they had it so long, it was “normal” for them. In the case of color blindness, I wouldn’t rule out, if he is a smart kid, he has learned how to cope on his own.
but, long and short, try to find ways to check this out yourself. Either indirectly, or, even just say to him, Grandma and Grandpa are wanting to help you, can you show us what is tough for you? do you know why you can see so well at night? do you have trouble with traffic lights? can you read this story to us? (if not, ask him if why he can read the TomTom, but not the book…Honestly…maybe he thinks the book sucks, and is beneath him, but the TomTom is exciting technology).
he is lucky to have you, someone who is concerned, and questioning…
Our son has a red/green confusion. He didn’t know it until he went to college and did a color blindness test during a class. Best part for him is that he can follow a blood trail through the grass and woods no problem.
I still can’t figure out how he came up with the right answers when h was learning his colors.
Great post:
I’m getting ready myself to put up a blog post on this very topic but as it applies to night hunting, as have been more than moderately successful at night hunting without the use of lights.
I will save your page and will list your post as a link when I put on my post on my blog.
Nick
Although your science is correct, most people with night vision knows it because they can see where everyone else cannot. Like me, most people asking this question does so over the course of many years, not just with family members. Otherwise we probably would just think we had good vision.
Sunlight hurts my eyes. Gives me headaches. I see much better at night many times. no moon, no starlight. I can hike in the dead of night. I just love how scientific minds sometimes cannot fathom things they aren’t used to dealing with. So closed minded when they sometimes should be curious instead.
I can see perfect details with no appearant light at all. (sp) And Bright light really hurts. I came here to ask why its this way, not to have it debunked when I know from experience its true.
I know not from friends or family members (who could attest to it) but from personal experiences that have nothing to do with comparisons in that fashion.
I live in a room with covered windows an a small lamp because light hurts my eyes and in complete darkness I can see every detail and every misplaced piece of clothing.
I just want to know why and if there is a medical term for it. For perfect night vision.