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UER Forum > Archived UE Tutorials, Lessons, and Useful Info > Night Adapted Vision (Viewed 1458 times) AnAppleSnail  Location: Charlotte, NC Gender: Male ALL the flashlights!  |  |  |  Night Adapted Vision < on 1/20/2013 5:29 PM >   I am a portable lighting enthusiast (Flashlight junkie) with interest in vision and its effects on humans. Low-light vision is useful. How does it work? NIGHT ADAPTED VISION Human vision is a powerful tool. It is a complex system that starts with the lens focusing light onto rods and cones. These light-sensing nerves send signals to parts of the brain that process the nerve stimuli into shapes. A few layers of brain turn shapes into recognized objects and we have vision. The dynamic range of human vision ranges from brighter than full sunlight to one billionth that brightness, and the eye's ability to see in the dark (Barring long exposure) is unmatched by any but the most specialized cameras. This vision lets us identify danger, navigate buildings, see distant things, and evaluate structures. Without vision, risks become harder to manage. There are three basic ranges of brightness our visual system operates in: Extremely dark (Scotopic), Very dark (Mesopic), and bright (Photopic). We all adjust 'up' more quickly than down, and individual ability to regain dark-adapted (Mesopic and scotopic) vision varies from person to person. Certain habits and techniques can improve this. Let's discuss low-light vision. First, science: Light itself is measured in watts. Visible light is measured in lux or candela, which accounts for how well we see various frequencies. One lux is one lumen per square meter. Lux add and compare easily. If I shine 400 lux on a surface, it will appear quite bright - about like an office would. In the dark (0.5 lux full moon), this looks blinding. During the day, shining 400 lux on a surface in a dark hole may not show up at all. In general, you need about 4x more light to look twice as bright. Rods and cones are chemical-reacting nerves that respond to different kinds of light based on the reactions of a few chemicals. Much like the cameras we built to copy our eyes, we have sensors that respond to light/dark, and sensors that respond to red, blue/violet, and green. Cones of all colors take about ten minutes to reach full adaptation. However, in truly dim areas (Less than a full moon's light, 0.5 lux), cones do not get enough light to respond to color. If you can see color, you are in the Mesopic visual range. The rods use a different chemical, Rhodopsin, that responds to low levels of light and turquoise. It does not respond well to red light. In bright light it is bleached, but mostly returns after five to ten minutes, and is fully back after about half an hour. Human visual sensitivity is like a mountain. Your central vision (Fovea) is meant for sharp detail in good light, and it is full of cones. The rest of your vision has far less detail, and your brain cleverly fills in details you can't see. Your best night vision will always be your peripheral vision. You are probably in photopic (Bright) vision, since you are reading this on a backlit screen. Color vision and visual acuity is good. This makes it easy to tell the condition of a wooden floor (Hint: Look at the wood ceiling above it), or see rusty pipes jutting out. Using a bright flashlight at night usually bumps you up into photopic vision immediately. But this is an inconvenience. At night, the light itself can draw attention. And immediately after you turn off the light, you see almost nothing. Maybe spots and specks. When the light gets dimmer, your contracted pupils begin to relax, taking about ten seconds. This acts exactly like the aperture on your camera. More light enters to strike your retina, and a greater blurring depth-of-field effect begins. The first stage of dark adaptation increases the light entering the eye by about 25 times (Which only magnifies apparent brightness by a few times). Your rods and cones do most of the physiological work in adapting to the dark. They immediately begin to become more sensitive to the reduced light entering your eye. Each works by light-sensitive chemicals being changed by light. Once light drops, there is more of the sensitive chemical ready to detect light, and sensitivity can increase. This transition often causes spots of false light - Your brain is misreading the chemical transition back to the low-light state of the sensitive chemicals. So: Seconds after you enter the dark, your pupils relax to let about 25 times more light in. Your rods and cones begin to adjust to lower-light operation. After about thirty seconds the spots tend to fade, and after about five minutes you can see under starlight or distant cityglow. It takes about half an hour to reach the full potential of your ability to see in the dark. And that ability is astonishing if you know how to use it. First, be careful. Night-adapted vision is much better than nothing, but far worse than photopic vision. You should move slowly and check carefully for damaged floors, sharp things, and use some common sense. It used to be I didn't expect to need this paragraph. But then again, I and both guys with me did successfully each hit our head on a light bracket in a dark tunnel, so... How does one use night vision? You adapt to the dark, protect your night vision, and use techniques to best take advantage of it. Adapting to the dark is easy: Wait in the dark for five to thirty minutes. Protecting your night vision involves some planning. If you see bright light for any length of time, you will reset your waiting clock completely. You can get around this by closing one eye. Try it in a very dim area. Close one eye for five minutes while walking there, then open it in the dark area. That eye will clearly see the grayish outlines of obstacles, and the other eye won't see a thing. This lets you use a (dim) light to check a map, read a text, or peek with a flashlight, without losing all your adapted vision. You can't look directly at what you want to see in real dark. Look to the side and move your head carefully. This gives you depth and a better outline to see what you are looking at. That helps see a silhouette and distance. Avoid bright lights and exposure to them. Close one eye if you can manage to, or calmly wait in the dark for night adapted vision to return. The down side to night adapted vision is that it's slow. You move slowly, adapt slowly, and still cannot see very well. But the benefits are great. For one thing, walking quietly in the dark makes you very hard to find. For another, it means you're ready even if your light fails. And finally, it lets you win bets and do newe things. Night adapted vision legends: 1. Red light is for night vision. Partly true, for extremely adapted vision. Deep red light does not especially reset your rods' sensitivity to light. However, most red lights today are red-orange LEDs rather than deep red LEDs or red-filtered filaments. They are also FAR too bright, well into the photopic range of output. This resets your cones AND your rods, and is quite visible to distant bystanders. Good flashlights for night vision are dim. An incandescent flashlight with a deep-red filter was the old standby, and this is why the military still insists on red (And where this legend comes from). A red light can work well, but must be quite dim and deep red. When you use such a light briefly, you will see with your cones, and not reset your rods. This reduces the vision adaptation time from half an hour to about ten minutes. During this adjustment time, you are still able to distinguish shapes fairly well. Red light is only better than very dim white light if you have been in deep dark for ten minutes. 2. Cyan/Turquiose/green is for night vision. False. Rods are most sensitive to turquoise, but they turquoise lights are too bright. This resets your rods and does not help your cones much. The military likes green because the other side's low-light gear (infrared) does not detect green very well. You do not want a green light for dark adapted vision UNLESS you can set it to the absolute minimum necessary for a task. This will be dimmer than your VCR's screen. Turquoise light of useful brightness for most things will probably reset your rods, and you may as well use white light. For fully-dark-adapted use, there is no substitute to a very-dim, deep-red light for added lighting. Nothing else will let you keep the full dark adaptation for truly dark areas. These include the middle of the woods on a moonless night, deep caves and tunnels, completely-boarded-up buildings, and really very few other places. Again, red only provides an advantage over very dim white light if you have been in true dark where you cannot perceive color, only shape, for ten minutes. I rarely find myself in full dark-adapted vision. If you are anywhere brighter than starlight (Anywhere near a city's skyglow, anywhere with windows facing streetlights, anywhere someone nearby has used a flashlight or lightpainted in the past ten minutes) you will be in mesopic vision. If you can see colors, you are not down in the scotopic range where a red light is the best tool. In these situations, a very dim white light is the best tool I have found. It allows fast and useful identification of hazards without excess scattering of light or reduction in light sensitivity. Very dim white light lets me identify rotten wooden floors, obstructions and signposts, and generally best enables seeing. The lights you want have very low outputs. 0.2 lumens. 0.04 lumens. These are the light levels you want. Shone ahead at a reasonable distance, this is in the 0.025-0.005 lux range that is the bottom end of mesopic vision. This is enough light to carefully walk around while identifying what you are walking on. Careful light discipline does the rest of making you hard to spot. How do you get dim lights? You can buy them. There is a very nice $25 L3 Illumination L10 out that has a 'firefly' mode. The Nichia 219 version is quite nice for colors, too. You can modify lights you already have. Adding an electrical potentiometer to some lights allows powerful dimming. You can also filter your lights. Light discipline: Using your lights in ways that won't get you caught. Do not shine the light towards windows or the horizon. Carefully use dim output and check before you use it. There are very few lights dim enough to be invisible when used improperly. Filters can do two things: Reduce and shape output, or reduce and color output. If you tie a black sock over a flashlight, you have a great light-reducing filter that makes it great for low-light use. You can also put duct tape over the front and add tiny pinholes to adjust the light. Some companies sell colored windows. These remove photons that are not the right color, and usually reduce output while adding a tint. Red is a common choice. You can DIY this effect with layers of packing tape colored with sharpie. It is common to put a snub on the end of a flashlight to reduce spill. This blocks light coming out at an angle, leaving the center spot for your use. This can help with reducing visibility, but also reduces your ability to see. There is a strong tunnel vision effect with concentrated light. It makes you move much more slowly, makes your eyes much more tired, and makes it more likely for you to run into things. So: Night vision comes in two flavors: Extremely adjusted and moderately adjusted. I find moderately adjusted night vision to be most useful most of the time. Moderately adjusted night vision takes about one minute to adapt and calls for dim white light to be most useful for safety and quick progress. Extremely adapted night vision takes ten to thirty minutes to adapt to and calls for unbelievably low output white light, or very dim, deep red light. Each technique has its place in exploring. I believe that I have shed some light on using them to see in the dark. Enjoy! And thanks for reading UE Tutorials, Lessons, and Useful Info. [last edit 1/20/2013 5:31 PM by AnAppleSnail - edited 1 times] Achievement Unlocked AnAppleSnail  Location: Charlotte, NC Gender: Male ALL the flashlights!  |  |  |  Re: Night Adapted Vision <Reply # 1 on 1/21/2013 5:25 PM >   tl;dr: Full dark adaptation takes about half an hour with very little light. If you can see color, you are in the low-light range and are not reaching full potential of dark-adapted vision. Dim, deep red light is the best low-level light when you have been in extreme dark for over ten minutes because it does not disrupt adapted vision. Red light does not activate your rods, preserving extreme the adapted vision. Most 'red tactical' flashlights are red-orange instead of red, and too bright for this use. Most situations are not this dark, in the mesopic range where a dim white light is the best option for navigation and low visibility. It takes almost as much visible red light as white light to see enough detail for safety, and white light allows better identification of hazards. You can buy flashlights with extremely dim modes (Less than 1 lumen) or add filters to existing flashlights with your hand, dark-colored cloth, or pinholed or slitted duct tape. Regardless of the low-level light you are using, flashlight discipline is far more important for avoiding detection than special flashlight gear. Achievement Unlocked AnAppleSnail  Location: Charlotte, NC Gender: Male ALL the flashlights!  |  |  |  Re: Night Adapted Vision <Reply # 2 on 1/21/2013 6:31 PM >   For the slow readers: Your eyes adapt to the dark very well but very slowly. In ten seconds you can see in 4x dimmer-looking light. In one minute you can see in about 40x better, and after half an hour you can see by starlight. Any light that is not VERY DIM or DEEP RED will instantly reset your adaptation and blind you. Keep bright lights off or covered, and stick to very dim (<1.0 Lumen) light or very dim deep-red light. Anytime you use a light brighter than this, you'll blind yourself and your friends for ten to thirty minutes while giving away your position. Use duct tape or a black sock or your hand on your flashlight. Or buy cool gear. Examples: L3 gear L10 4-mode. The dim mode (0.09 lumen) is very good for mesopic (Quite dim) vision. If you run it with the light mostly covered, it works for scotopic vision. Bad examples: Mag Lite 2D. This flashlight will blind anybody near you, just like the advertisements say, but you don't want to blind your friends. Do you? This is one to use a filter on. To preserve the front window, stick a paper circle on the front for flood, or backwards-duct-tape for more reach. Now stretch duct tape across the front and poke pinholes in it. The backlit paper gives you a floody beam through these holes with low output. Do not use big holes. If it looks really dim at home, it's perfect. [last edit 1/21/2013 6:31 PM by AnAppleSnail - edited 1 times] Achievement Unlocked keti  Moderator Location: Providence, RI Gender: Female #EA98DE  |  |  Re: Night Adapted Vision <Reply # 3 on 1/22/2013 6:00 PM >   Very thorough post, thanks for sharing! Lots of useful info here. [23:38:31] <metawaffle> I'm surprised the NE forum doesn't fall off UER from the weight of thread locks uer.ca is like / being in the mob / basically, a / ninja mob. - Aleksandar Lamouette/rck  Location: Lévis Gender: Male Recykle toi !  |  Re: Night Adapted Vision <Reply # 4 on 2/15/2013 4:54 PM >   Thanks a lot ! great to learn interresting things ! and really helpful to choose a flashlight ! Do you know, if there is something one the human who can adapt him everytimes to dark place ? (like children always growing in dark, or something like that (it's difficult to explain, my english is quite bad ) or if everytimes his eyes will be re-adapted to the light ? Sure our body need light, but maybe our eyes could work differently ! Bye ce n'est pas parce qu'ils sont beaucoup a avoir tord qu'ils ont raison ! AnAppleSnail  Location: Charlotte, NC Gender: Male ALL the flashlights!  |  |  |  Re: Night Adapted Vision <Reply # 5 on 2/15/2013 9:45 PM >   I don't know of anyone who has tried growing up in the dark. Generations living in complete dark lose functioning eyes, like the albino cave fish. I don't know about long-term effects on an individual, though. Achievement Unlocked AnAppleSnail  Location: Charlotte, NC Gender: Male ALL the flashlights!  |  |  |  Re: Night Adapted Vision <Reply # 6 on 2/15/2013 9:46 PM >   Hm. Everything is delayed at ATL. [last edit 2/15/2013 9:52 PM by AnAppleSnail - edited 1 times] Achievement Unlocked twinpowered  Location: BC, Canada Gender: Male Every photo tells a story.  |  |  Re: Night Adapted Vision <Reply # 7 on 6/3/2013 9:17 PM >   Posted by AnAppleSnail like the albino cave fish. Featured in BBC's Planet Earth! Very thorough post, thanks! Interesting read, but I think I'm sticking to using flashlights. AnAppleSnail  Location: Charlotte, NC Gender: Male ALL the flashlights!  |  |  |  Re: Night Adapted Vision <Reply # 8 on 6/5/2013 11:49 PM >   Posted by twinpowered Very thorough post, thanks! Interesting read, but I think I'm sticking to using flashlights. Thank you. I am too, but there are times that I use dimmer lights or no lights as appropriate. I don't pretend to be a Splinter Cell Ghost Recon ninja, but it's interesting to try truly dark adapted vision on night hikes. Amazing what you can see by starlight half a kilometer down a pit. Further research shows that avoiding bright light.sources helps to speed and enhance dark adaptation. So a person who needs to see well in the dark should wear decent sunglasses during the day. I think that's acclimation, not adaptation. [last edit 6/5/2013 11:51 PM by AnAppleSnail - edited 1 times] Achievement Unlocked XCorneliusX  Location: Central FL Gender: Male  |  Re: Night Adapted Vision <Reply # 9 on 7/23/2013 1:23 AM >   On an explore in April I took a strong beam with me, and those I was with, as well as a very very low lumen mini. We were at a Nike site and it was completely dark save for some mild ambient light from above. My eyes were indeed night adjusted and using that mini I was able to see some detail where I was walking or pre scout a couple of my not so good pics. I was able to see quite well actually in the dark. It is very different than my preferred super bright neutrals I have from Malkoff Devices http://www.malkoff...03a8743fcc060c4c76 What I like in the neutrals vs cool or warm light is the neutral brings out color and every single grain of dust and detail. Pretty cool stuff. Anyway, in reading the excellent post by AnAppleSnail, I remembered I have a micro torch of white and another of red. Both are Coast products and would have also been very well suited for that explore. Downside, though not too down, is they use a special BR435 3V lithium battery I have found on Amazon and eBay. In locating one, the white micro, I found its batteries were done. So, in thinking about this post I just ordered 2 more of the red and 4 batteries from Amazon. The micro red led is here. http://www.amazon....roduct/B0002SR63O/ lovelife  Location: D-Town Gender: Male Hide yo kids, Hide yo wife  |  Re: Night Adapted Vision <Reply # 10 on 11/8/2013 9:43 AM >   I usually eat a large bag of raw carrots an hour before I go out exploring, which eliminates any need for flashlights. And i only explore with the strobe setting. The standard setting is for squares. People tend to get a little upset with me, but it's the only way to truly live. -Relik supersidalicious  Location: Boulder, Colorado Gender: Male  |  Re: Night Adapted Vision <Reply # 11 on 11/9/2013 10:53 PM >   Thanks for posting this! Like you suggested, I always try to enforce flashlight discipline when I'm outside during the night hours for multiple reasons, but I'll have to try your DIY methods for flashlight dimming sometime! lovelife  Location: D-Town Gender: Male Hide yo kids, Hide yo wife  |  Re: Night Adapted Vision <Reply # 12 on 11/13/2013 7:31 AM >   It WILL work! I promise! And i only explore with the strobe setting. The standard setting is for squares. People tend to get a little upset with me, but it's the only way to truly live. -Relik UER Forum > Archived UE Tutorials, Lessons, and Useful Info > Night Adapted Vision (Viewed 1458 times) All content and images copyright © 2002-2024 UER.CA and respective creators. Graphical Design by Crossfire. To contact webmaster, or click to email with problems or other questions about this site: UER CONTACT View Terms of Service | View Privacy Policy | Server colocation provided by Beanfield This page was generated for you in 140 milliseconds. 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