Red Light

[Heinz Doofenshmirtz]

I actually use a green freedom micro when tagging along with my wife (who is the big astronomy buff in our family; she has a 10" dobsonian reflector).  I like it a lot better than the red because I get much better depth perception using it than with a red light.  With red lights, my eyes tend to focus to infinity when dark adapted and I can't read jack when that happens.  With the green light, the improvement in depth perception I get allows me to still read and stay dark adapted.  Another advantage of the green ones is that you can substitute a single 2032 in them for the two 2016's they come with, and effectively cut the output of the light in half because of the reduction in voltage from the 32 compared to the 16's.  This lets the light go to a lower low and keeps the high from being too high, which it can easily do running 2016's.  It took a little while for the other members of the local astronomy club to get used to it, but the green works so much better for me, that I refuse to go stargazing with her without it.

[mainstream]

red laser should not be best choice, you may lost in the dark when you come across the places where mix the red and the green light together.

[mzil]

I haven't played much with using green as an alternate night vision preservation color, but since Photon specifically makes one I also now have made a green filter disc for my silencer attachment mod as well. Since the filter discs are almost paper thin , I keep the alternate one I'm not using in the Photon's battery compartment. This way with a small screwdriver, like I carry on my Leatherman PS4 attached to my keychain, I can open the battery lid and swap colors in the field, at a moments notice, if I desire.

Here is the green filter disc in action (but at full blast for photographic purposes; for night use a dimmed setting would be used) along with the red filter shown left out of its normal battery storage compartment and a spare filter retaining puck prior to being blackened with a black Sharpie pen in the foreground.

[mainstream]

how about this one, SPAMCORP.com/3-in-1-Blue-LED-Torch-Flashlight-Red-Laser-Pointer-Pen_p95649.html]http://www.SPAMCORP.com/3-in-1-Blue-LED-Torch-Flashlight-Red-Laser-Pointer-Pen_p95649.html[/url]
 it is does really a cheapie and also fit you want.3 in 1 Blue LED Torch Flashlight Red Laser Pointer Pen with just $1.95,i just came across it recently.

[mzil]

^ That's an interesting product which coincidentally I have had recent interest in, however for people like the OP and myself who have an interest in reading star charts and looking at things in dark environments while preserving our night vision, a red laser is of no use. We need a large area of light coverage, like a flood light, instead of a focused point, which also can be dimmed to very low levels. Traditionally red is associated with this however I have read reports from reliable sources which seem to indicate that although red works better than white, it is actually not as good as green or turquoise green and the real reason people have been using red all these years is because red light is the color of choice for dark room applications when developing photographic film because of film's relative insensitivity to it compared to other colors in low light and not because of the claimed reason people state regarding human's vision and how rods and cones work.

See, people incorrectly associated the red color used in dimmed darkrooms with  what a human would want for astronomy chart reading (while preserving night vision for when you then look through the telescope and need the most dark adapted eyes as possible, to see faint details like in nebulae). Whereas red was selected becuse of film, not humans.

[Neil]

Red or pure green get the job done. The reason red is normally chosen for low level night lights is that when map reading contour lines can still be seen.

[mzil]

^Thanks Neil. I've heard various claims about:

"You need this color for seeing outlines (contours)"

"You need that color for reading standard newspaper sized text  against a white paper background."

"You need this other color if you expect to have some degree of depth perception"

"You need this yet fourth color because although it doesn't preserve night vision sensitivity especially well what it does do is let you return to your fully dark adapted state twice as fast as the other colors."

Unfortunately all of these claims come from various vendors and forum members, none of which I'd exactly call "disinterested and unbiased". What I'd really like to see is the original research to back these various claims. Might you know of any?

[I started a thread on this very topic in the candlepower forums and all it did was ignite a flame war between rival camps (which I had nothing to do with) causing it it get shut down by the mods.]   

[Tabasco]

Mzil, here is a article you may be interested in: http://stlplaces.com/night_vision_red_myth/

I have no horse in the night adapted race, but my neighbor belongs to the local astronomy club. It's a interesting, ecletic group of people with very strong opinions on night vision and lighting. They use everything from various flashlights to GITD devices, many homemade.

 On a side note, my father taught us, when possible, to keep one eye closed for a hour or more, before and after dusk, to maintain a pretty decent level of night vision. Simple and effective.

[mzil]

Thanks Tabasco, that was great!

Keeping one eye night adapted is a technique I've used too.

[Heinz Doofenshmirtz]

That article was correct.  I'm a university professor with a PhD in perceptual and cognitive psychology.  The idea behind the green light for night vision use is that is closest to the wavelength that the rods are responsive to, so it results in better night vision than a red light.

I can go into *much* more detail if you like, but I'll leave at that for now unless anyone wants to know more specifically about response characteristics of the rods and cones to different wavelengths and how that influences our perceptions of color and brightness.

[mzil]

^ OK, Thanks.

I just had a crazy idea but please hear me out and keep an open mind before dismissing it. This following scenario might not work well for a star party with more than one person but what about for a single person star gazing alone?

Instead of filtering the flashlight's output why not filter the individual eye's input? Use a pair of, say, swimming goggles with red filtration on one eye for close focusing and map reading purposes and green/blue on the other for maximum dark adaptation. The goggles are worn throughout the entire time except when viewing through the telescope when the green/blue lens is temporarily lifted for full unfiltered light exposure from the eyepiece. With such goggles the external flashlight one buys would be normal white light, increasing the number of candidates tremendously [plus it works as a normal flashlight when not star gazing]. If one made the red and green/blue filters dark enough, perhaps by adding in neutral density gray as well, one wouldn't even necessarily need to buy a flashlight with dimmed output; the goggles do that job. Again this greatly increases the number of flashlight candidates one could utilize.

[Another variation would be one goggle red (or green) and the other entirely blackened. You lose stereoscopy but the eye kept in the dark is always in optimal dark adaptation mode and fully protected from unexpected light while the other can read, do telescope assembly, etc.

Pros:
-Wearing light dimming eye wear reduces the eyes' dark adaptation time (because you've artificially made your environment even darker than "starlight illumination only").
-One light serves both purposes. No need to keep both a red filtered and green filtered  one on hand.
-Unexpected car headlights or visiting people with normal flashlights don't ruin your session.
-Special dedicated flashlights with variable dimming may (or may not) be acceptable if the goggles are made dark enough through the inclusion of neutral density filters on top of the color filtration.

Cons:
-You look funny. 
-From a distance a third party watching you wouldn't realize you were maintaining dark adaptation because from their perspective you would appear to be sitting in the dark but occasionally turning on a normal, garden variety, white flashlight. [well maybe a dim one but not typical "stargazing" dim]

ETA: A flipper version for eyeglass wearers might be good. Sort of similar to these (although they should be darker and the blue should be more green) :



 
 

[Heinz Doofenshmirtz]

mzil,

It's a creative suggestion, but the problem is that it would create what is called binocular rivalry.  It would create a conflict in the integration of the separate inputs from each eye into a single perceptual experience.  Some research studies have shown that when people are presented with two separate images in each eye, say a dog in one and a cat in the other, they sometimes perceive an illusory combination of the two separate images. 

Another issue that arises from binocular rivalry is that one eye tends to be more dominant than the other; this is easy to see when you look at something and check for the amount of parallax shift you get from closing one eye and then the other.  The eye that you see the lesser amount of parallax shift is your dominant eye.  So for people with a strong dominance they would see only the input from the dominant eye, rather than a combination of the two inputs.  As the amount of dominance lessens, the more likely someone is to see the combined illusory image of both inputs. 

In a strong ocular dominance situation, eventually that eye and the corresponding areas of the visual cortex in the brain will fatigue, and the person will experience an involuntary shift in the perceived image because the non-dominant eye is not providing a stronger signal to the brain.  Once this eye and its associated brain areas then fatigue, the perception would shift back to the now rested dominant eye, and so on.

While we know a lot about the wiring and functioning of the visual system, how the brain creates an integrated perceptual experience is still more or less a mystery...  In perceptual psychology we call it the 'binding problem'; how is it that we have a unified perceptual experience when the way the brain works is by separating out the different components of perceptual input... color processed in one place, shape in another, motion in another, object identity in yet another, and so on.  Honestly, it's a question that may ultimately be unanswerable in term of just the neurophysiology of the brain and visual system.

We know that the brain does this division of labor partly from looking at people with specific perceptual deficits caused by brain damage from strokes, or injuries, and so on.  One such example of this kind of deficit is known as prosopagnosia; the inability to recognize a face as a face.  People with damage in what is called the fusiform face gyrus, a ridge of gray matter in the brain's cortex, in the inferior left temporal lobe, suffer from prosopagnosia. 

What's more, the damage is selective to the integrated perception of a face; patients with this condition can still correctly answer questions about a picture of someone's face about what color their eyes are, whether they're smiling or frowning, what the shape of their nose is, etc. but they can't see all those individual components as a face.  And this extends even to line drawings such as smiley faces...  So what this shows us is that the fusiform face gyrus is an integration area, it takes input from other parts of the brain that separately process the individual features such as the eyes, nose, mouth, etc. and puts them together to create our perception of a face.  This even extends to faces of non-humans; there was a case of a dairy farmer in england who knew all of his cows individually who suffered a stroke that resulted in prosopagnosia; not only could he not tell his wife's face from anyone else's, he couldn't tell his cows apart from one another just by looking at their faces!

And, if that wasn't wild enough, for people who have damage in this area in the right temporal lobe but not the left, they can recognize faces, but they can't tell you if the expression on the face is happy or sad, angry or whatever, although they can still tell Fred from George, they just can't tell you whether it's Fred or George who is the angry one. 

[NutSAK]

Great discussion here!  Thanks for sharing your knowledge HD.

[mzil]

mzil,

It's a creative suggestion, but the problem is that it would create what is called binocular rivalry.  It would create a conflict in the integration of the separate inputs from each eye into a single perceptual experience.

Yet the majority of people can sit through an entire old style 3D movie wearing almost exactly analogous red / blue anaglyph glasses and report both a successful experience of stereoscopy and only a few with headaches. I'm just talking about the 20 minutes or so it takes to let the eyes fully adapt to the dark, not during the actual viewing through the telescope or anything else. The only task one would have while doing this is tripod and telescope assembly. Would the binocular rivalry be so discombobulating one just couldn't for the life of them attach the scope to the tripod? I find that a little hard to believe, however if your concerns panned out as true and your perception goes so kaflooey from the binocular rivalry, then the alternative I suggested of one eye being fully obscured, (the dominant one you actually then later use for telescope observing) and the other one getting the color filtration for telescope and tripod set up, could be utilized. Although not ideal, most people can do most simple tasks even with one eye covered, even reading.

Have you ever personally tried covering your dominant eye once both have become fully dark adapted and then turning on a light to use exclusively your non-dominant eye in a bright room? You can get around just fine (not driving, etc) and then when you turn the lights back off and uncover your protected eye, SHAZAM, instant night adapted vision! [albeit without stereoscopy because the weaker eye is now light fatigued] Try it tonight when you wake up in the middle of the night to let the dogs out (or pee, in my case ).

Are you one of the lucky 1% of us that uses a telescope with a binocular eyepiece assembly (like a Nagler "binoview")? Not me. Your perception is from a monocular view when you use most scopes and people have no problem with it so I don't see why one eye being obscurred during telescope assembly should be such a big deal. I'm not talk about walking around all day, driving, or operating dangerous machinery with this contraption on one's eyes, I'm talking about in the 20 minutes or so that it takes the eyes to get adapted and the pupils fully dilated, would one be able to successfully assemble their tripod/equatorial mount, unbag their eyepieces, etc. with this less than ideal, but only temporary eye wear? I suspect the answer is "yes".

[Heinz Doofenshmirtz]

Considering the consistency of the input, other than the color, in general yeah, it should work.  They key is that you'd still be looking at the same scene/image while wearing them, so the rivalry effect would be rather minimal actually. 

With respect to depth perception, two different colors, as per the old anaglyph style 3D glasses, would increase depth perception, but again, that's where the rivalry comes in.  I honestly can't say how it would affect someone for longer term wear... 

In some ways, it's not really necessary though with the use of something like a 'night vision' green (I'll have to look up the wavelength for that) because it's at a wavelength that will stimulate both the rods and the green cones.  It is the stimulation of the cones that provides the depth perception.  They are wired into a system of retinal ganglia cells that are specialized to encode detail as well as the green we perceive from it.  It is the basis of all shape perception; it begins with edge detection and enhancement and consists of a densely packed set of overlapping areas, each which receives stimuli from only a small portion of the visual field (which is why the encode detail), and much of our depth perception comes from that. 

It's the fact that the green light engages this system that allows me to keep my detail vision when dark adapted and so I can still read when using the green light.  With the red light actually, even the rod are not very strongly stimulated by it, because its a wavelength pretty far from what rods are tuned to receive, so with red the parvocellular system is not engaged.  (And that's why a red light has to be really intense to be perceived as bright; which I suspect has added to the reasoning for using red lights for preserving night vision, they just don't seem as bright at low levels.)

It wouldn't even be necessary to expose both eyes either, one could very easily simply patch one eye for total scotopic adaptation and still have good depth perception because the majority of the cues in visual information for depth perception are monocular; while quite powerful, there are only about 1/4 as many stereoscopic cues as their are monocular cues.  So in short, you'd still get good depth perception with one eye.  (However, patching would increase fatigue effects because the entire visual processing load is being handled by only half of the visual system.)

Over prolonged periods of time, there would most likely be some effects from fatigue because of the rivalry, but how strong it would be or how long before it became a problem would vary from person to person.  (Getting more caroteines in the diet helps vision because the pigmented protein in photoreceptors, rhodopsin, is based on it.  Supplementing your diet with more caroteines, as well as omega-3's, would help reduce the effects of fatigue.)

[Heinz Doofenshmirtz]

Great discussion here!  Thanks for sharing your knowledge HD.

Not at all; my pleasure.  This is what I teach, and what my research is about.  I love talking about this stuff. 
 

[mzil]

In some ways, it's not really necessary though with the use of something like a 'night vision' green (I'll have to look up the wavelength for that) because it's at a wavelength that will stimulate both the rods and the green cones.  It is the stimulation of the cones that provides the depth perception.

Photon's (LRI) genuine Turquoise green "night vision" LED light is 450 nm, not that I have proof they know what they are doing, and it is said to also have a wider flood pattern than most of their other colors (which sounds good to me).

If I were to construct either the two color or one color with eye patch goggles I've described, using a white light then filtered at the eye instead of the flashlight's output [and test them on myself as a Guinea pig, avoiding of course dangerous environments, tools, machinery etc], what tests might I apply to test the effectiveness? Reading? Putting pegs in holes (screws in equatorial mount is more like it)? Might you have a link to what battery of tests might be applied?

Besides a possibility of temporary nausea, are there any dangers from a short term, say 20 minute exposure?

Thanks.

[Black Rose]

Mzil, here is a article you may be interested in: http://stlplaces.com/night_vision_red_myth/

Interesting article.

For the longest time I was using a Gerber Infinity Ultra with the red LED to navigate at night, but recently started using a multi-mode white light (1.8 lumens on low).

[Heinz Doofenshmirtz]

In some ways, it's not really necessary though with the use of something like a 'night vision' green (I'll have to look up the wavelength for that) because it's at a wavelength that will stimulate both the rods and the green cones.  It is the stimulation of the cones that provides the depth perception.

Photon's (LRI) genuine Turquoise green "night vision" LED light is 450 nm, not that I have proof they know what they are doing, and it is said to also have a wider flood pattern than most of their other colors (which sounds good to me).

If I were to construct either the two color or one color with eye patch goggles I've described, using a white light then filtered at the eye instead of the flashlight's output [and test them on myself as a Guinea pig, avoiding of course dangerous environments, tools, machinery etc], what tests might I apply to test the effectiveness? Reading? Putting pegs in holes (screws in equatorial mount is more like it)? Might you have a link to what battery of tests might be applied?

Besides a possibility of temporary nausea, are there any dangers from a short term, say 20 minute exposure?

Thanks.

I'll have to look up the wavelength that the rods are most sensitive to.  I seem to recall it's somewhere around 475, but I'm not sure off the top of my head; I'm just too lazy right now to actually pull out a book and check.

I don't think you'd have too much trouble, as long as you weren't trying to juggle knives or pick up and carry hot coals, etc.; in other words, anything inherently hazardous.  I'd suggest test of depth perception and acuity; reaching out to pick up things, and trying to read smaller point or finer text would be the most demanding impromptu tests you could do. 

As far as I know, other than any inherent hazards in the tasks you'd be attempting with the filters on, you shouldn't have any problems other than some nausea and perhaps some disorientation and dizziness.  The longer you wear them, the more adapted you'll become...  There is a famous experiment from back in the late 1800's, one of the founders of experimental psychology, Francis Donders, did an experiment with prism goggles; the wore a pair that shifted his line of sight about 20 degrees to one side from where he was looking...  he wore the goggles 24/7, even when he was sleeping, and at first had a great deal of difficulty just doing common tasks.  After about two weeks, he was acclimating to them pretty well, and one night he went to sleep, and when he woke up the next morning, he no longer saw the offset shift.  He could reach right where he was looking and pick up whatever he wanted without having to compensate for the shift.  At that point he took the goggles off, and everything was wacked again... he again saw the shift and had to re-acclimate!  This was with the goggles off remember!!!  He also did the same experiment with goggles that invert the image, and had exactly the same results.  So there is something in the brain that takes that kind of thing into account and adapts to it.  So in the short run, I don't think you'd have too much trouble, but be careful just to be safe.  You also might want to consult an ophthalmologist for a second opinion as well.

[mzil]

I was web surf and look what I found. Seems like some low life in the past took a time travel trip to the future, read this thread, including my idea to filter the eyes with colored goggles instead of coloring the outputs of the lights we use, stole my idea, went back in time to where he came from and  wrote this, giving me absolutley no credit. GRRRRR:

"ENHANCING AND MAINTAINING DARK ADAPTATION

Red Goggles or Spectacles

For maximum utilization of scotopic vision, 20 to 30 minutes in total darkness are required to attain satisfactory retinal dark adaptation. An alternative is to have the aircrew member wear red goggles for 20 to 30 minutes before flying. When worn in normal illumination, red goggles will not interfere significantly with the ability to read most maps, charts, manuals, etc., as long as the printing is not in red ink. Red goggles block all light except red, which enhances rod dark adaptation because red light does not stimulate the scotopic system."

Well if people in the past are going to steal my ideas like this I'm just gonna take my ball and go home. Huff!

[Gareth]

   damn those time-travellers!

[Sparky415]

Thanks Guys this has been a very interesting thread
Good ideas and lots of information 

[ICanFixThat]

^Thanks guys. It is very simple to make:

1. Cut the top off of a BIC "Round Stick" pen cap  like the one shown in the photo, using a sharp single-edged razor blade or similar scalpel like knife. This is the silencer's main body.

2. Gut the remaining pen shaft of its ink tube and ball-point assembly and insert this empty tube into the newly made main body so the front of the two are flush with each other.

3. Using the razor knife, slice off the section that remains outside the main body and discard.

4. Remove this inner, short cylindrical section you just made and slice it into two even shorter cylinders, roughly one being a third and the other being 2/3's. These make up the two red filter retaining pucks which will sandwich the red filter disc between them when re-inserted.

5. Unless you are luckier than me and found a BIC pen with a black main body to begin with, make the two retaining pucks black by coating them on all inner and outer surfaces with a black indelible marker (eg. Sharpie). You don't have to be neat since very little will be exposed anyways. You just want to make the white plastic non reflective.

6. Cut a round disc of the filter material which has a diameter equal to the inner diameter of the main body. It doesn't have to be perfectly round. I used:
http://www.google.com/products/catalog?q=midwest+products+pvc+red+704+03&oe=UTF-8&hl=en&cid=11128150600755133795&os=contents
that I bought locally at an art supply store (as well as a green sheet for further experimentation some day).

7. Insert one retaining puck, then the filter disc, and finally the other retaining puck making sure the larger puck section is for the Photon's nose end. I found friction alone held it all together rather well but glue could be used or small wedges of filter material if you want to making the retaining pucks more secure.

Keep in mind this works because the nose of the Photon Freedom Micro covert http://www.google.com/search?q=photon%20freedom%20covert&rls=com.microsoft:en-us:IE-SearchBox&oe=UTF-8&rlz=1I7ASUT_en&um=1&hl=en&ie=UTF-8&tbo=u&tbs=shop:1&source=og&sa=N&tab=if&biw=880&bih=753  is a cylinder with the same size as the inner diameter of the BIC pen tube. Here is the silencer shown removed, for when you want white light:

(Image removed from quote.)

By painting the inner walls of the "silencer" pucks black with the black marker and recessing the filter disc inside away from the front surface a few millimeters, I've maintained the "covert" status (no side light emitted), important for stealth use and better for astronomy applications as well.

Fantastic!