# Is using red light for "preserving night vision" simply a myth?



## mzil (Aug 16, 2010)

Ever since I was a boy all the telescope/astronomy magazines would pitch flashlights with red light claiming that "red light helps preserve human's night vision and keeps your pupils dilated so you can still see well in low light when you turn them off". Up 'til now I've always accepted that but I've never seen any scientific evidence for this other than marketing, testimonials, and various anecdotal stories. 

For all I know the_ real_ reason red lights work at preserving human's ability to see in low light (by keeping the pupils from contracting) is simply because when you put a color gel or filter over a white light you reduce its output greatly and this reduced output is really what preserves one's night vision; _the color has nothing to do with it!_

I've been experimenting with attaching my own DIY red filters to some flashlights but I'm wondering if this is really in vain since they have a variable output from dark to light capability in the first place and I simply should be using _that_ instead. Hmm...

*Does anyone have any links to scientific articles, ideally in scholarly journals, that have tested if red light truly helps preserve human's night vision as opposed to simply dimmed light or using other colors?* Testimonials, anecdotal stories, and marketer's pitch stories I can find _thousands_ of examples of; that's not what I'm looking for. 

Thanks.


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## sween1911 (Aug 16, 2010)

mzil said:


> Ever since I was a boy all the telescope/astronomy magazines would pitch flashlights with red light claiming that "red light helps preserve human's night vision and keeps your pupils dilated so you can still see well in low light when you turn them off". Up 'til now I've always accepted that but I've never seen any scientific evidence for this other than marketing, testimonials, and various anecdotal stories.
> 
> For all I know the_ real_ reason red lights work at preserving human's ability to see in low light (by keeping the pupils from contracting) is simply because when you put a color gel or filter over a white light you reduce its output greatly and this reduced output is really what preserves one's night vision; _the color has nothing to do with it!_
> 
> ...



Interesting question! I've always accepted it at face value. Here's an article on Flashlight Reviews with a little backround on physiology: http://www.flashlightreviews.com/qa/nightvision.htm


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## badtziscool (Aug 16, 2010)

The show Mythbusters actually did a piece on night vision. They didn't really touch on using red light but they explained the night vision concept.

The light receptors in your eyes gets desensitized when it's exposed to light, and the brighter the light, the more desensitized it gets. That's why when you go from a lighted room to a dark room, it takes a while for the receptors to calm down and become more sensitive. With that being said, I would think your theory with using a red filter and it reducing the brightness of the light is valid. But to add to that, I think its because red has the lowest frequency in the visible spectrum and thus the has the least energy. So therefore, it is the color that's least likely to over-stimulate the receptors and will help preserve your night vision. But that doesn't mean it preserves it completely. Many times, I've been camping or night hiking and when i use a red light for a prolonged period of time, I do lose a little bit of night vision, but it comes back to me much quicker than if I used a full spectrum light.


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## Blue72 (Aug 16, 2010)

sween1911 said:


> Interesting question! I've always accepted it at face value. Here's an article on Flashlight Reviews with a little backround on physiology: http://www.flashlightreviews.com/qa/nightvision.htm



good link, just make sure the red light is around 1 lumen


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## wyager (Aug 16, 2010)

badtziscool said:


> But to add to that, I think its because red has the lowest frequency in the visible spectrum and thus the has the least energy. So therefore, it is the color that's least likely to over-stimulate the receptors and will help preserve your night vision. But that doesn't mean it preserves it completely. Many times, I've been camping or night hiking and when i use a red light for a prolonged period of time, I do lose a little bit of night vision, but it comes back to me much quicker than if I used a full spectrum light.


The problem with the whole energy idea is that your eyes are very insensitive to red light. A mW of green light will easily be 10x brighter to your eyes than a mW of red light (even though they are exactly the same energy). So by this logic, green should be the best for night vision as it is the lowest energy. However, I don't think this works. There would have to be another reason for red to preserve NV if this were true, and I don't think "it's dimmer" is a valid reason as then you could just use a dim white light.

EDIT: I just read that link, it explains it very well.


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## Chucula (Aug 16, 2010)

> Does anyone have any links to scientific articles, ideally in scholarly journals, that have tested if red light truly helps preserve human's night vision as opposed to simply dimmed light or using other colors? Testimonials, anecdotal stories, and marketer's pitch stories I can find thousands of examples of; that's not what I'm looking for.



Suppose you find that scholarly journals claim red light is a myth. Are you going to believe them blindly and ignore all of your personal experience, assuming that it is automatically right because "scientists" said so? What if you find two articles that contradict each other? 

Buy a red and white keychain light, go into a dark room, and test it yourself. If it works or doesnt work for you, go by that. It is pathetic to ask "scientists" if something looks a certain way to _your _eye.

FWIW, I keep a red photon freedom next to my bed because regular white lights, even on low mode, shock my dark-adapted eyes.


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## gcronau (Aug 16, 2010)

There was an excellent article on how night vision works in an issue of Astronomy magazine way back in the 70's. (Don't ask me for the volume and issue number. The best I can do is that it was probably around 1976 give or take a year.)

The numbers quoted were interesting. Going from a very bright room to a very dark one will cause your pupils to expand fairly quickly, but the increase in light gathering from pupil dilation is only about 10x.

The real increase comes with changes to the sensitivity of the retina. Over a period of at least an hour, the retina's sensitivity can change by up to 100,000X. For a total change in light sensitivity of ~1,000,000X.

Many things can affect how sensitive the retina can become including age, past or present eye deseases, whether you smoke, what drugs are in your system, etc.

Also, if you've spent the day exposed to very bright light, it will take much longer for your eyes to reach their full sensitivity and will limit how sensitive they can become on a given night. For example, a day spent out in the sunlight at a beach without sunglasses might limit your eyes from becoming fully dark adapted for several days. Some astronomers would wear red goggles and stay indoors for the entire day(or two) before an important night of observing.

So, the issue with red light hasn't got anything to do with pupil dilation, it's about retinal sensitivity.


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## JNewell (Aug 16, 2010)

Not a scientific, quantitative answer but I can tell you from actual experience that a relatively high output red damages my night vision more than a low output YG. 



mzil said:


> Ever since I was a boy all the telescope/astronomy magazines would pitch flashlights with red light claiming that "red light helps preserve human's night vision and keeps your pupils dilated so you can still see well in low light when you turn them off". Up 'til now I've always accepted that but I've never seen any scientific evidence for this other than marketing, testimonials, and various anecdotal stories.
> 
> For all I know the_ real_ reason red lights work at preserving human's ability to see in low light (by keeping the pupils from contracting) is simply because when you put a color gel or filter over a white light you reduce its output greatly and this reduced output is really what preserves one's night vision; _the color has nothing to do with it!_
> 
> ...


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## elgarak (Aug 16, 2010)

Red light is preferable over white (or other colors), but the explanation given is wrong. I give references; you can google them, but I don't know if you can get the original articles. I can, being on a university network. Libraries should be able to get them, though.

The standard explanation already given is wrong, since both cones and rods react the same above wavelengths of 650 nm or so (red), but rods are much more sensitive at lower wavelengths, thus their night vision gets killed [S. Hecht and Y. Hsia, J. opt. Soc. Am. 35 (1945)]. Thus, for the same 'brightness experience' (for lack of a better understandable term) of red and white light, the eyes will recover more quickly if red light is used [E. O. Hulburt, 'Time of Dark Adaptation after Stimulation by Various Brightnesses and Colors', J. opt. Soc. Am. 41 (1951)]. It's not that red will protect night vision, but destroys it much less than white.

However, red light loses its advantage with lower brightness (and I'm talking really low brightness here). If you don't need much brightness, you can get away with low intensity white [S.M. Luria and David A. Kobus, 'The Relative Effectiveness of Red and White Light for Subsequent Dark-Adaptation', Naval Submarine Medical Research Laboratory, Report 1036 (1984)]. White has the advantage of giving you sensitivity of a full color spectrum over any monochromatic source. It essentially makes no sense to restrict your eyes to the sensitivity of just one color, since you will need much higher brightness with the one color to get the same 'brightness experience' as with white.

As always, YMMV. The above articles assume 'normal' 'average' vision. If you're color-blind, for instance, your cones and rods react differently anyway, and it may not work for you.


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## wyager (Aug 16, 2010)

Chucula said:


> Suppose you find that scholarly journals claim red light is a myth. Are you going to believe them blindly and ignore all of your personal experience, assuming that it is automatically right because "scientists" said so? What if you find two articles that contradict each other?


Ever heard of the placebo effect? Sorry, I trust "scientists" over any of the pathological science a single person will generate lol...


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## elgarak (Aug 16, 2010)

After doing some more reading, it's important to note differences in procedure. The Submarine Report I referenced, for instance, assumes that most people in the submarine just need to work their equipment, while a few need to prepare themselves for night vision. None of them is truly dark adapted, but they want to reduce the time required for getting dark adapted. The authors of the report conclude that for this case, low white is essentially as good as red, without the annoying problems of red.

But for most of us, the problem is different as follows. Your eyes are already dark adapted, and you just need a quick flash of light to locate a piece of equipment or operate the telescope, if you're doing astronomy observations, for instance. From my understanding of the curves, for this case it's much safer to stick with red, as low intensity as possible, to reduce the damages to night-vision as much as possible. IMHO.


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## Casper507 (Aug 16, 2010)

Red is still the standard for use for light discipline in the military. A red filter cuts the light output. It REALLY cuts the output of a LED light vs a incan in my experience. I had a lens break in a 5 mode cr123 flashlight and I trimmed a red filter from my minimag kit and it made a huge difference in light output.


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## mzil (Aug 16, 2010)

Chucula said:


> Suppose you find that scholarly journals claim red light is a myth. Are you going to believe them blindly and ignore all of your personal experience, assuming that it is automatically right because "scientists" said so?



The short answer: YES!

I can't speak for everyone in this forum, but me, myself, I'm a human being, subject to the placebo effect, observer bias, and any number of other foibles.

Remember, _always_ trust your eyes. _They never lie_:









If the image appears to be in motion, _then it_ _must be_. 
---

My understanding of night vision has little to do with with rods and cones, but rather that once your pupils dilate to 7mm* or so after 5-20 minutes in the dark, some colors of light _supposedly_ re-constrict them less than others.

*[There is actually a very large variance, but that's the _average_, hence the most common pair of hand-held binoculars for astronomy are 7x50, because their exit pupil, the objective diameter in mm. divided by the magnification, matches the average human's night adapted eye's pupil diameter.]


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## Mr Bigglow (Aug 16, 2010)

I'm going in with some of the previous posts. If you live your life relying on scientific articles and not actual life experiences, then you will live a very interesting life indeed. Science, like statistics, can be used to 'prove' almost anything. Experience, now, tells us that people like sailors and soldiers and yes astronomers all use weak red light to preserve their nightsight, and I have too. It works. It works better than other colour lights but they also work to some extent. Better you set out to test that and then to prove why (or why not) than to rely on already published articles. But if you do want to do the authorities thing, I can point you to, for instance, about 10,000 food supplements that were once 'proven' to do something they didn't. And to more than a few that actually made things worse.


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## wyager (Aug 16, 2010)

Mr Bigglow said:


> I'm going in with some of the previous posts. If you live your life relying on scientific articles and not actual life experiences, then you will live a very interesting life indeed. Science, like statistics, can be used to 'prove' almost anything.


Absolutely 110% completely wrong. The way science is presented can be misleading, Eg "Tasers have been know to cause death" would suggest that tasers are deadly in general. However, if you actually lived on scientific information and didn't take things at face value, you would realize the full statement is something like ".0001% of people tased died" (just as an example). Science has no agenda, and true factual information can not be used to prove anything false, except by human error. The scientific method prevents such a thing from happening. Personal experience is irrelevant next to scientific research.


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## Nos (Aug 16, 2010)

Its not that hard to get


http://en.wikipedia.org/wiki/Scotopic_vision

http://www.instrumentationguide.com/article/photopic_sctopic.htm

thats why you want red to keep your visoin night adapted


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## elgarak (Aug 16, 2010)

Mr Bigglow said:


> I'm going in with some of the previous posts. If you live your life relying on scientific articles and not actual life experiences, then you will live a very interesting life indeed. Science, like statistics, can be used to 'prove' almost anything. Experience, now, tells us that people like sailors and soldiers and yes astronomers all use weak red light to preserve their nightsight, and I have too. It works. It works better than other colour lights but they also work to some extent. Better you set out to test that and then to prove why (or why not) than to rely on already published articles. But if you do want to do the authorities thing, I can point you to, for instance, about 10,000 food supplements that were once 'proven' to do something they didn't. And to more than a few that actually made things worse.


And if you ignore science and its peer reviewed publications, you end up getting a lot of woo and BS.

If one person says it works, without controls and procedures, it's anecdotal evidence. It's pretty much useless information.

If ten people say it works under controlled conditions with proper procedures and repeated experiments, it becomes science.


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## KenAnderson (Aug 16, 2010)

Rods and cones...

Cones are for color.

Rods are for black and white.

Rods are not affected by low red light, cones are.


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## elgarak (Aug 16, 2010)

KenAnderson said:


> Rods and cones...
> 
> Cones are for color.
> 
> ...



Nope. Above ~650 nm light wavelength (red), both rods and cones are affected pretty much the same.

Low red light DOES inhibit dark adaptation. However, it does it MUCH LESS than white, or other colors. A dark adapted eye that gets low red light will recover faster back to dark adaptation than the same eye exposed to white light of comparable brightness. Even so, at really low brightnesses this advantage is pretty slim. If you need to find your way around, low light of any color is about the same. If you need to read something (i.e., need a little more light than just to detect obstacles), but want to disturb your night vision as little as possible, stick with red.


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## elgarak (Aug 16, 2010)

Here are the relevant graphs from the papers I referenced.

First, the usual way the scotopic (rods) and photopic (cones) sensitivity of the human eye is usually depicted:



That's where the original usage of red for night vision came from. It seems to indicate that the rods don't do much in the red. But it ignores that the scotopic rods are a lot more sensitive than the photopic scone -- essentially, both curves should not go up to one on the vertical axis! This graph is normalized, done for illustration purposes! (The curve is also very smooth, and there are no data points. That's usually a pretty good indicator that this is not a 'real' measured curve, but an illustrative curve. In this case it unfortunately does not illustrate what we are interested in.)

In reality, it looks like this:



As one can see, both curves pretty much overlap above 600 nm. So, red light for night vision is just a myth. Or is it? After all, anecdotal evidence (as provided in this thread) seems to show that red IS better for night vision. Let's test it scientifically.

If one tests how well people can actually see in the dark after exposing their eyes to red or white light, one gets this:



The vertical axis shows how bright a test object needs to be to be seen. The horizontal axis shows how much time elapsed after exposure. Some notes:

1) Both red and white affect night vision negatively (the hump at the left).
2) Red is always better than white -- people can see fainter objects, and the time to recover is shorter.
3) At low brightness (the bottom graph), white and red are very close.
[sidenote: One should note that white exposure is always lower than red. That's been done to take into account that people need a little bit more red brightness to see than with white]

If one takes the time it takes to reach perfect night vision (the flat horizontal part in the graphs above), and plots them against the brightness used to expose the eyes, one gets this:



As one can see, at about 10 footcandles (108 lux) of illumination, white starts to perform a lot worse than red. Below that, it's still better to use red, but not by much. To put things in perspective, 10 ft-cd is about the illumination needed to read (as in: make out the letters on a menu. I personally whip out my EDC in restaurants that use such low light levels to read the menu). And before someone asks, it is not possible to recommend a lumen value for a light from this. As one can always move the light farther away to reduce the illumination level, and the lumen value does not take into account the 'spotness' of the particular light.

Hope that resolves things.


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## ebow86 (Aug 16, 2010)

A red light to perserve night vision isn't much good to me becuase I'm bound to blast off the high beam anyway, thus destroying my night vision, but I can see where alot of people find it useful.


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## JNewell (Aug 16, 2010)

Interesting post and discussion. Some of the conclusions surprise me. I'm not going to throw Wikipedia at the discussion, though. 




elgarak said:


> Red light is preferable over white (or other colors), but the explanation given is wrong. I give references; you can google them, but I don't know if you can get the original articles. I can, being on a university network. Libraries should be able to get them, though.
> 
> The standard explanation already given is wrong, since both cones and rods react the same above wavelengths of 650 nm or so (red), but rods are much more sensitive at lower wavelengths, thus their night vision gets killed [S. Hecht and Y. Hsia, J. opt. Soc. Am. 35 (1945)]. Thus, for the same 'brightness experience' (for lack of a better understandable term) of red and white light, the eyes will recover more quickly if red light is used [E. O. Hulburt, 'Time of Dark Adaptation after Stimulation by Various Brightnesses and Colors', J. opt. Soc. Am. 41 (1951)]. It's not that red will protect night vision, but destroys it much less than white.
> 
> ...


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## [email protected] (Aug 16, 2010)

Concentrating to the question of red Vs. green for night adapted vision, this has been hashed out quite a bit on these forums and I'll "reuse" the answer I gave then...



[email protected] said:


> I'm definitely no expert in ALS (Alternative Light Sources) though CPF does have it's share, my understanding was...
> 
> * *Rods* are our night adapted vision receptors (most sensitive to blue/green) primarily located in our peripheral optic regions, don't interpret colour OR movement
> * *Cones* are responsible for specific detail & colour (most sensitive to red) primarily in our centered optic region
> ...



And...



[email protected] said:


> Obviously green light effects the Rod cells and to a lesser extent the Cone cells due to their 3-way cell distribution (which varies from one individual to the next) of the three types of Photopsin utilized by the Cone cells the largest proportion are sensitive to Long light Wavelengths of 500~700nm (predominantly Red).
> 
> Considering our Cone cells are responsible for detail & acuity it seems only logical that this is the reason for the NVG's applied color frequency and use of green ALS's in field for map reading and up close detail work
> 
> ***Current school of thought seems to support the application of "significantly" low level white light for non-military and hunting/tracking applications allowing the engagement of both the Cones and to a lesser extent the Rod cells of the eye for night orientation/navigation as a means of avoiding the associated "night blind spot" resulting from peripheral only night adapted vision



Experiments conducted by G. Wald determined that the Rod cells were insensitive [should read less sensitive] to wavelengths above 640nm (Red), thus red light's only negative impact on our night adapted vision is it's intensity, low level red simply works! :thumbsup:






_Normalised absorption spectra of human Long, Medium & Short wavelength Cones & Rods cells_


FWIW Cones division (which varies person-to-person) are explained rather well by Wikipedia HERE


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## wyager (Aug 16, 2010)

[email protected] said:


> What a truly sad and skewed perspective... if science is always 100% correct why do we have members of the scientific community arguing about global warming? scientific ideology is nothing more than the current "collective agreement" reached through repeatable experiments OR interpretation of data collected using the scientific approach/method...
> 
> Remember they once thought the world was flat, the earth was at the centre of the galaxy & the atom was the smallest structure in the universe, trust your personal instincts/experience and only use "current science" as a guide :candle:


Science IS always correct, barring human error. That's what I said. The thing about global warming is this-the fact that the earth is warming is undeniable, but whether or not it is a natural cycle is arguable. We don't have sufficient data to satisfy the scientific method about global warming yet. And then of course, there are people who argue things like "evolution is not real". But of course, this is just human error. Spitting in the face of scientific evidence does not count as science, and should be ignored.

They thought the earth was flat because they were raised to ignore facts and not follow the scientific method. No respectable scientist said that the earth was flat, but only because there were no legitimate scientists studying the earth in places they thought it was flat (some societies were aware it was round). Any people that actually followed the scientific method were burned at stake, so you got a lot of human error.


Our science now is amazing-and we have almost removed human error from science, as we now have machines that will perform complex mathematics and logistics without fail. I trust our science a lot more than the "science" of the past. I certainly trust it more than my own personal experience, beyond the fact that I have to experience the science.


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## [email protected] (Aug 16, 2010)

[Off Topic]


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## wyager (Aug 16, 2010)

"Okay so again I ask you... was science correct when they unequivocally stated that "the atom" was the smallest object in the universe?"

Occam's razor. No more should be presumed to exist than absolutely necessary. The existence of sub-atomic particles was not important to science at the time. That's like asking why the Aztecs were smart if they didn't know about electromagnetism.

"Take the "scientific method" and apply it in your personal life don't trust someone else to do your thinking for you, make up your own mind that's why you've got a brain"

I've never let anyone decide for me any more than is necessary. However, sometimes you just have to trust others. A. priori knowledge is still useful. I've never used an electron microscope, but I still trust the people that have when they say computer chips are made out of silicon.


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## OceanView (Aug 16, 2010)

Although debating the scientific method and the evolution of human understanding of the natural world may make an interesting college course, we're terribly off-topic here. :thumbsdow 

Why do night vision threads often bring out the worst in flashaholics? :shrug:


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## [email protected] (Aug 16, 2010)

OceanView said:


> Although debating the scientific method and the evolution of human understanding of the natural world may make an interesting college course, we're terribly off-topic here. :thumbsdow



Agreed I will delete off topic commentary :naughty:


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## elgarak (Aug 16, 2010)

[email protected] said:


> Experiments conducted by G. Wald determined that the Rod cells were insensitive to wavelengths above 640nm (Red), ...


No, he didn't.

See my previous post, second graph. Read the caption. That's Wald's data. Which DOES show sensitivity still at 700 nm... (Never trust Wiki. Check the original source.)


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## Nitro (Aug 16, 2010)

I do a lot of star gazing. I, like most astronomers know when I've achived good night vision. But even more important I know how long it takes for it to return after seeing light. If I go inside with a white light, even if dim, it does take longer to get my night vision back than if it's red.

I purposely have a red bulb in my garage, which is pretty bright, that I use when star gazing. My night vision is preserved after being around the red light. The only time I have a problem is if I stare directly at the bulb. But if it were a white bulb and I stared directly at it, my night of star gazing would be over.

Something else that's interesting that most astronomers know is there is no color when star gazing. Your eyes can't detect color in very low light. Also you see less detail. However, a trick you can do is look just to the side of the object. After a while your mind will gather the image in more detail than if you were looking directly at it.

As far as science goes: Science, statistics, politics, religion, law have all been used by persons to push an agenda. As the old sayings, "Figures don't lie, but liars figure", and "Don't believe your own eyes." come to mind.


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## kramer5150 (Aug 16, 2010)

I find that any color tint if low enough will preserve my night adapted vision. Warmer tints, amber, orange and red I find "easier" on my adapted vision. By that I mean less "blinding" upon initial exposure, and shorter time to recover once exposed.

My opinion is based on my own observations with my 3 lights. I have three different moderate-low output lights. A Lenser, nite-ize minimag and a SF-A2. All 3 use 3x 5mm emitters, and drive them fairly hard to maximum output levels. The surefire and Lenser use Nichias. I know for a fact that the SF-A2 slightly overdrives its red LEDs. Of the 3 the red A2 is by far MUCH more easy on my night adapted vision. It takes me less time to adjust and recover with the red tinted SF.


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## mzil (Aug 16, 2010)

elgarak said:


> As one can see, both curves pretty much overlap above 600 nm. So, red light for night vision is just a myth. Or is it? After all, anecdotal evidence (as provided in this thread) seems to show that red IS better for night vision. Let's test it scientifically.



Yes, and thanks for these charts (which none of us have access to) and would you kindly do me (us) a favor and clear some things up since you can read the actual articles (I can only find brief summaries):

A) "Time of Dark Adaptation after Stimulation by Various Brightnesses and Color*s*"

Liars! You only tested red vs white (going by the charts). Blue green etc never got tested.

B) "Thus red is better than white at preserving, or at least reducing the time to restoring, night vision once exposed."[paraphrased]


How exactly was this tested? After the antagonistic light exposure were the subjects then pressing a button at the lowest level that they could reliably detect a light bulb had been turned on _staring right at it_? Asked to read text and getting an accuracy score of 75% or better, or what? The submarine tests seemed to be judging the ability to see silhouettes against a starry sky, or something similar, but the other test I need more details, please.

C) "After testing the subjects ability to (lets say) read the text with a 75% accuracy level after exposure to the four test voltages using the white light bulb, we then repeated the test exactly but instead substituted the red light bulb." [paraphrased]

_Hello! McFly!_ Red light bulbs are white ones that have been painted red so they obviously will have a reduced output and yield better results simply because they are dimmer and that you haven't accounted for! [People in this thread who claim red is superior haven't indicated they made any attempts to account for this either, I might add.]
---

Slightly off topic, but I'll bring it up anyways:

There are two kinds of people interested in red light. An astronomer wants to be able to read sky maps and find things in a bag while preserving night vision as best possible, and number two, a sniper who also wants to preserve night vision but even more so doesn't want to give away his (her) position. But isn't _*red*_ light, the internationally accepted color of attention getting (think a bike light) about the stupidest color to use for a sniper? Hey look at me, over here!:wave:


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## mzil (Aug 16, 2010)

Nitro said:


> Something else that's interesting that most astronomers know is there is no color when star gazing. Your eyes can't detect color in very low light. Also you see less detail. However, a trick you can do is look just to the side of the object. After a while your mind will gather the image in more detail than if you were looking directly at it.



I can see the Andromeda Galaxy with the naked eye, using this "averted vision" technique, which is 2.5 million light years away, if I recall correctly. As far as I know that is the farthest distance a human can see! [We are also on a collision course with it, so that's cool too!]

Some stars _do_ have discernible color, BTW:
http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html


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## elgarak (Aug 17, 2010)

mzil said:


> Yes, and thanks for these charts (which none of us have access to) and would you kindly do me (us) a favor and clear some things up since you can read the actual articles (I can only find brief summaries):
> 
> A) "Time of Dark Adaptation after Stimulation by Various Brightnesses and Color*s*"
> 
> ...



This is from the Hulburt ("Time of Dark Adaptation after Stimulation by Various Brightnesses and Colors") paper:

1) They did indeed use three different monochromatic light sources. Remember, this was 1951, so the choices were limited. The monochromatic lamps were gas-discharge lamps, which produce a handful of discrete lines; for instance, a sodium vapor discharge lamp gives off one visible yellow line at 589 nm (actually, two lines at 589.0 and 589.6 nm. Standard test lamp to test a spectroscope during my lab classes. If you could see both lines with a simple grid spectroscope as they use in chemistry, you were good). Unwanted lines were filtered. Additionally, they used a Tungsten-incandescent with filters, which were not as well monochromatic, but pretty narrow band. The red was done with the filters used in Navy night vision protecting goggles (this was done at the Naval Research Lab in Washington, D.C.). Yes, the brightness of those lamps were calibrated. They used a (70% reflectivity) so called stimulation screen that was illuminated by those lamps, and they could adjust the brightness of this screen by adjusting the distance. A light meter was used to calibrate the brightness.

2) The night vision was tested with a target screen with a dot on it that was illuminated with a tungsten lamp turned so low that the screen itself was just at the threshold of being visible dark adapted. When the eyes became closer to dark adapted, one would see first the screen, then the dark dot on it. I had to do similar experiments myself while studying for my (German) Physics diploma, and this is quite doable and fascinating to see. The target lamp was shielded so that the light would only hit the screen, not the test person. The sizes of the screen, dot and distance to the test person were chosen so that the screen would appear under a viewing angle of 24 degrees, the dot under an angle of 1 degree.

3) The procedure was as follows. Test person would dark adapt the eyes. Then turn on the stimulating screen and look at it for a defined period of time. Then turn off the stimulating light, and wait (with a stopwatch) until one sees the target screen, and then the dot. Stop the time. The target screen was on all the time, since it was so low brightness that it didn't matter. Repeat often and take the average time. Get as many people (students at a university  )as possible and do it with them.

All clear? Very hands on. Those guys were hard-*** physicists. But it's pretty much the newest data I could find. Essentially, no one thinks it's worth repeating (except for torturing Physics students). Hecht, Wald, Hulburt nailed it (Hecht did build a mechanical shuttered device to turn on and off targets (essentially model stars) and stimulating light in the 1920s, and then spent about 25 years using that thing to experiment with it). All the newer papers is 'just' detail stuff, how each functional building block in the eye does work to produce these effects.

Oh, and about 'no color during stargazing': Sure, the rods do not detect colors. But stars ARE differently colored, and with a large enough telescope you can see those colors with your own eyes. Essentially, the objective opening diameter needs to be large enough to collect enough light. My old school had a telescope large enough -- forgot how large exactly, and unfortunately not often enough available (plus, usually lousy weather in Germany, and a lot of stray light). But once I saw Betelgeuse, and got perfect seeing. Amazing! The air between my eye and Betelgeuse would become perfectly still for just a moment, and the fuzzy blinky blob I saw did shrink to this perfect pinpoint with an amazing red-orange hue. Just beautiful.

About red being a stupid choice: Nature's a *****. Red is the only color that does have any good effect.


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## [email protected] (Aug 17, 2010)

elgarak said:


> Low red light DOES inhibit dark adaptation. However, it does it MUCH LESS than white, or other colors. A dark adapted eye that gets low red light will recover faster back to dark adaptation than the same eye exposed to white light of comparable brightness.



So we agree all light effects all of the eyes cells absolutely? BUT low level red light effects the rods the least of all, how is this any different from what we've already posted? :thinking:


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## Nitro (Aug 17, 2010)

mzil said:


> People in this thread who claim red is superior haven't indicated they made any attempts to account for this either, I might add.


 


Nitro said:


> If I go inside with a white light, *even if dim*, it does take longer to get my night vision back than if it's red.


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## MikeAusC (Aug 17, 2010)

*The right answer for the wrong question ?*

If you don't state your question very carefully, don't be surprised if you get the "wrong" answer -

A. What colour light should I use so I can use the least lighting power where I need to recognise colours ?

B. What colour light should I use so I can use the least lighting power where I only need to be able to see fine detail e.g. read text ?

C. What colour light should I use so I can use the least lighting power where I only need to recognise shapes but not fine detail ?

D. What colour light should I use so I can see fine detail e.g. read text, but when I LEAVE this lit area, I will still have maximum sensitivity under starlight ?

E. What colour light should I use where I only need to recognise shapes but not fine detail, but when I LEAVE this lit area, I will still have maximum sensitivity under starlight ? 

F. What colour light should I use so I can still recognise colours in low lighting levels, but that light will not affect the sensitivity of Night Vision Goggles to Infrared.


If you can't see that these are questions about very different situations, you're wasting your time on this thread.

If you think the answer to all these questions is the same, you're wasting your time on this thread.


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## Nitro (Aug 17, 2010)

elgarak said:


> Oh, and about 'no color during stargazing': Sure, the rods do not detect colors. But stars ARE differently colored, and with a large enough telescope you can see those colors with your own eyes. Essentially, the objective opening diameter needs to be large enough to collect enough light. My old school had a telescope large enough -- forgot how large exactly, and unfortunately not often enough available (plus, usually lousy weather in Germany, and a lot of stray light). But once I saw Betelgeuse, and got perfect seeing. Amazing! The air between my eye and Betelgeuse would become perfectly still for just a moment, and the fuzzy blinky blob I saw did shrink to this perfect pinpoint with an amazing red-orange hue. Just beautiful.


 
I have an 11" SCG. Actually, I can see the colors of the cloud belts on Jupiter, and color in some stars. But it's not enough to see the colors in nebula (bummer). Astrophotography, on the other hand will show colors very nicely.


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## MikeAusC (Aug 17, 2010)

mzil said:


> Some stars _do_ have discernible color,


 
If you mean discernible by the eye, then it just means there's enough light reaching your eye to activate the Cones.

If we depended on eyes only, we could assume that moonlight consisted of only bluish light - but if you take a photograph under moonlight, objects have the same colour as under sunlight.


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## elgarak (Aug 17, 2010)

MikeAusC said:


> If you mean discernible by the eye, then it just means there's enough light reaching your eye to activate the Cones.



While searching for papers on dark adaptation, I came across one where the scientist investigated the color perception at low light levels. Turns out that people DO experience color even when the cones are not activated due to low light levels. The current hypothesis is that the brain interpolates colors based on previous experiences (as if the brain goes: "These kinds of objects are most often blue. I make that one blue"), but it's not quite clear what exactly happens.


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## OceanView (Aug 17, 2010)

*Re: The right answer for the wrong question ?*



MikeAusC said:


> If you don't state your question very carefully, don't be surprised if you get the "wrong" answer


Excellent point, Mike! The OP's general question about "preserving night vision" can be taken in different ways, as you rightly point out. Which is probably why night vision threads often degenerate into arguments. People are often trying to address different aspects of "night vision" and unfortunately, the evidence can appear contradictory depending on which specific question you're trying to apply that evidence to.

It's unfortunate that the scientific literature is quite thin and old. There must be military and corporate studies (e.g. aircraft or vehicle manufacturers) who have done some interesting work, but it's probably considered classified or trade secrets.


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## Mr Bigglow (Aug 17, 2010)

wyager said:


> Absolutely 110% completely wrong. The way science is presented can be misleading, Eg "Tasers have been know to cause death" would suggest that tasers are deadly in general. However, if you actually lived on scientific information and didn't take things at face value, you would realize the full statement is something like ".0001% of people tased died" (just as an example). Science has no agenda, and true factual information can not be used to prove anything false, except by human error. The scientific method prevents such a thing from happening. Personal experience is irrelevant next to scientific research.


 
Yes, what I said. _Science_ has no agenda, _scientists and others_ often do. It is science that reveals the truth in the end- but only when or if anyone pursues the issue. I have no problems with the scientific method, but the scientific method is generally faked or, more often, incomplete in citations in the media.


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## DM51 (Aug 17, 2010)

*Re: The right answer for the wrong question ?*

mzil, I have temporarily removed your post from view. I can understand you thought it might be in order to quote another member's PM because he wanted to spare your feelings by posting it and you didn't mind that, but it is still an infraction of Rule 12 unless you have that member's specific authorisation to reproduce his private correspondence to you. He might well have chosen different words for a public post; and he may have had other reasons for not wishing to post at all.

If you obtain his authorisation (or if he sends it to me direct) then I will reinstate your post. Failing that, you will need to paraphrase or summarise what he said in a manner that does not breach the confidentiality of his original private correspondence.


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## mzil (Aug 17, 2010)

^Understood.

*To: ______* do you authorize me to publish your entire PM to me, verbatim, or should I simply put it in my own words and paraphrase what you wrote instead?

Thanks.


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## DM51 (Aug 17, 2010)

I suggest you PM him. I've deleted his name from your post.


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## mzil (Aug 17, 2010)

^Done. I have sent a reply PM to his asking permission to publish his messege in full, verbatim, in the thread itself and have specificlly asked for confirmation to this request to be put in the thread itself or in a direct PM to you, DM51.

Thanks.
---
Back to the topic.

I read in an astronomy forum (if I recall correctly) that about half of the astronomers in attendance at a recent gathering (star party? expo? telescope show?) said they just used dim pocket lights and thought that the red color aspect was simply baloney/myth. I'm still trying to relocate where I read that and will report back if I re-find it.


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## BackBlast (Aug 17, 2010)

wyager said:


> Science IS always correct, barring human error.



That's kind of like saying, I have a gold nugget in my hand, but without the gold (it's a rock). Science is a system devised by humans, humans can err. Until you find a flock of perfect humans, that don't err, then any system they run (IE science) cannot be defined as being "always correct" because at it's core, it's run by imperfect humans. Who can, you know, cheat and lie.



> That's what I said. The thing about global warming is this-the fact that the earth is warming is undeniable, but whether or not it is a natural cycle is arguable. We don't have sufficient data to satisfy the scientific method about global warming yet. And then of course, there are people who argue things like "evolution is not real". But of course, this is just human error. Spitting in the face of scientific evidence does not count as science, and should be ignored.


[sarcasm]Yes! All hail science![/sarcasm] What science is really, a search methodology. An imperfect one at that. Can science detect what is not externally observable? No, it intentionally EXCLUDES that realm. Does that mean anything not externally observable doesn't exist? That's one view of the world, but a limited one IMHO because it is incorrect. There are many previously unobservable realms which only recently entered observability, there are probably many more such and there could be another set that will never be observable in the manner a science user needs. 

Science has it's place, it does work well for some thing. But lets not go overboard with science worship... I believe the more humble adherents realize these limitations whereas some take it way too far and take on an arrogant attitude of all-encompassing unflappability.



> ...[snip science praise]...Our science now is amazing-and we have almost removed human error from science...


If only it were true... Our engineering prowess has improved through discoveries, and you may well conclude that our discovery methodologies are good using that as evidence. But engineering prowess does not eliminate human character flaws or inherent declared omissions to a methodology.


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## Nitro (Aug 17, 2010)

BackBlast said:


> That's kind of like saying, I have a gold nugget in my hand, but without the gold (it's a rock). Science is a system devised by humans, humans can err. Until you find a flock of perfect humans, that don't err, then any system they run (IE science) cannot be defined as being "always correct" because at it's core, it's run by imperfect humans. Who can, you know, cheat and lie.
> 
> [sarcasm]Yes! All hail science![/sarcasm] What science is really, a search methodology. An imperfect one at that. Can science detect what is not externally observable? No, it intentionally EXCLUDES that realm. Does that mean anything not externally observable doesn't exist? That's one view of the world, but a limited one IMHO because it is incorrect. There are many previously unobservable realms which only recently entered observability, there are probably many more such and there could be another set that will never be observable in the manner a science user needs.
> 
> ...


 
+1

Don't forget... Science breaks down at the center of a Black Hole and the beginning (and end) of the Universe.

Science, Mathematics, Religion, Politics, Law, Philosophy ALL turn into a belief at a fundamental level. NOTHING can be proven without accepting (believing) some basic Axioms (truths) to be true. You can't prove 1 + 1 = 2 without accepting (believing) that 1 exists.


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## Solscud007 (Aug 17, 2010)

I use red light all the time at night. For navigating in my house to use the bathroom. as a kid i learned early one to keep one eye closed when i turn on the bathroom lights. the white light would hurt my open eye. I would pee, then turn the light off and return to my room. the eye that i kept in the dark helped me navigate in the dark.

I get a similar result by using red light with my Kromas and Surefire helmet light. The red light illuminates everything, but it doesnt screw up my night vision as white light of a similar brightness. My kroma with high red is pretty bright. it actually hurts my eyes. But I notice that I can still see things when i turn off the red light. Not the case with white light.


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## wyager (Aug 17, 2010)

Nitro said:


> Don't forget... Science breaks down at the center of a Black Hole and the beginning (and end) of the Universe.


It doesn't break down at all! The science just changes... and it's not like we've ever looked inside a black hole to determine such a thing (protip-you can't send information back out, information is a tangible thing ). As for the beginning, we only have to look to quantum mechanics. The end, we don't know much about.


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## Kraid (Aug 17, 2010)

I have nothing scientific to contribute, but I can say that when I throw my SureFire flip top red filter over my Malkoff MC-E, it still messed up my night vision. Although not nearly as much as with the tip off!


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## elgarak (Aug 17, 2010)

BackBlast said:


> That's kind of like saying, I have a gold nugget in my hand, but without the gold (it's a rock). Science is a system devised by humans, humans can err. Until you find a flock of perfect humans, that don't err, then any system they run (IE science) cannot be defined as being "always correct" because at it's core, it's run by imperfect humans. Who can, you know, cheat and lie.
> 
> [sarcasm]Yes! All hail science![/sarcasm] What science is really, a search methodology. An imperfect one at that. Can science detect what is not externally observable? No, it intentionally EXCLUDES that realm. Does that mean anything not externally observable doesn't exist? That's one view of the world, but a limited one IMHO because it is incorrect. There are many previously unobservable realms which only recently entered observability, there are probably many more such and there could be another set that will never be observable in the manner a science user needs.
> 
> ...



Being a scientist, I m appalled by your attitude, and the way you present it. Now, of course you have the right to believe what you want, as I have the right to believe you are wrong. But I believe your attitude stems from multiple misconceptions about science and scientists. Other people have said it better than I ever could, and I hope that the following video may help you to identify your misconceptions.

Eric Schulze, "Things I Should Have Been Taught About Science.", PhD Candidate, Keck School of Medicine, University of Southern California, Commencement Speech.


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## wyager (Aug 17, 2010)

elgarak said:


> Being a scientist, I m appalled by your attitude, and the way you present it. Now, of course you have the right to believe what you want, as I have the right to believe you are wrong. But I believe your attitude stems from multiple misconceptions about science and scientists. Other people have said it better than I ever could, and I hope that the following video may help you to identify your misconceptions.
> 
> Eric Schulze, "Things I Should Have Been Taught About Science.", PhD Candidate, Keck School of Medicine, University of Southern California, Commencement Speech.


Thanks. I didn't want to spend my time making a response to that post, you did it for me.


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## Nitro (Aug 17, 2010)

wyager said:


> It doesn't break down at all! The science just changes...


So anytime Science fails, we just change it? :laughing:

You just proved my point. i.e. Nothing is certain, not even Science.


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## Nitro (Aug 17, 2010)

elgarak said:


> Being a scientist...


Can you prove 1 + 1 = 2?


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## wyager (Aug 17, 2010)

Nitro said:


> So anytime Science fails, we just change it? :laughing:
> 
> You just proved my point. i.e. Nothing is certain, not even Science.


LOL no, it's like the difference between quantum laws and relative laws.


Nitro said:


> Can you prove 1 + 1 = 2?


1+1 does not always equal two


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## entoptics (Aug 17, 2010)

BackBlast said:


> Science is a system devised by humans, humans can err. Until you find a flock of perfect humans, that don't err, then any system they run (IE science) cannot be defined as being "always correct" because at it's core, it's run by imperfect humans. Who can, you know, cheat and lie.



Only people ignorant of science suggest that science is perfect (or worse, that scientists think it is perfect). In fact, the most fundamental principles and procedures in the scientific method are specifically designed to weed out honest error and intentional deception.

The beautiful irony is, that whenever people criticize the fallibility of science, they bring up examples like Piltdown man, flat earth, geocentrism, Korean cloning, etc, etc. Last time I checked, it was science that eventually ruled out all of the above all by itself.



BackBlast said:


> Can science detect what is not externally observable? No, it intentionally EXCLUDES that realm. Does that mean anything not externally observable doesn't exist? That's one view of the world, but a limited one IMHO because it is incorrect. There are many previously unobservable realms which only recently entered observability, there are probably many more such and there could be another set that will never be observable in the manner a science user needs.



The above is a straw man in it's entirety, and actually mostly false. Science by no means excludes anything. It does, on the other hand, only lend weight to observable, repeatable, testable conclusions.

Again, the irony is delicious. "Previously unobservable realms which only recently entered observability". Who was it that finally observed them? Preists? Pizza delivery drivers? Lawyers? Leprechauns?...Hmmm...nope, Scientists.

Regardless, what exactly is "unobservable" and who exactly can observe the unobservable? If someone observes it...doesn't that make it un-unobservable...

:shrug:



BackBlast said:


> I believe the more humble adherents realize these limitations whereas some take it way too far and take on an arrogant attitude of all-encompassing unflappability.



+1. Lets not forget the opposite scenario though. It takes some pretty impressive arrogance to disregard the thought process that got a man on the moon.



BackBlast said:


> ...engineering prowess does not eliminate human character flaws or inherent declared omissions to a methodology.



+1. Correct. Scientific methodology takes care of that with its system of testing, pear review, and the generally most vicious and cut throat system of thinking ever devised by man. Half of a scientists career is coming up with new ideas, the other half is the methodical testing and destruction (and in rare cases confirmation) of other peoples ideas.

This seems on topic to me, as the OP specifically mentioned "scientific articles" and his aversion to anecdotal evidence.


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## entoptics (Aug 17, 2010)

Nitro said:


> So anytime Science fails, we just change it? :laughing:
> 
> You just proved my point. i.e. Nothing is certain, not even Science.



Actually, yes. That's the beauty. In other words, you just proved our point. Not that we need the help, but thanks anyway.


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## KiwiMark (Aug 17, 2010)

Nitro said:


> Can you prove 1 + 1 = 2?



1 + 1 = 3 for very large values of 1.


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## Nitro (Aug 17, 2010)

entoptics said:


> Actually, yes. That's the beauty. In other words, you just proved our point. Not that we need the help, but thanks anyway.


So I guess we're both right, and wrong at the same time. I guess I can't argure with that, and yes I can. LOL


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## wyager (Aug 18, 2010)

Nitro said:


> So I guess we're both right, and wrong at the same time. I guess I can't argure with that, and yes I can. LOL


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## entoptics (Aug 18, 2010)

Nitro said:


> So I guess we're both right, and wrong at the same time. I guess I can't argure with that, and yes I can. LOL



+1

P.E.A.R.L (physical evidence and reasoned logic) a.k.a. science is simply VERY good at catching itself when it's wrong. It may seem slow to us small folk, but in terms of "world views" or belief systems, it's got a pretty good track record of successfully correcting mistakes.

90,000 years of chest pounding nomadic wondering then bam, beer, libraries, pyramids, aqueducts, telescopes, electricity, combustion engines, penicillin, computers, bad *** flashlights, and this fun conversation all in less than 10,000 years.

w000t!


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## Nitro (Aug 18, 2010)

I think this is getting WAY off topic, but I'll state this last word. Then I'll open a new thread in the Cafe if anyone wants to discuss it further.

For the record I love Science, Math etc etc etc. I think we need it just like we need a set of laws, constitution etc. However, it is my belief that Science (i.e. man) will never be able to understand everything. In other words, there will never be a system (laws of physics) that will describe the Universe i.e. "Theory of Everything". We will always need to have some faith. We will always have to just accept (believe) some things to be true. Otherwise we won't know the truth about anything.


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## KiwiMark (Aug 18, 2010)

Science ain't perfect, but it's the best & most accurate stuff us highly imperfect creatures have. If science says that red light reduces rod sensitivity the least then that is good enough for me (for now anyway, if someone proves otherwise then I'm happy to re-evaluate what I believe).

All I know is that red light doesn't cause pain in my night adapted eyes like white light does. Although really dim white light isn't too bad (Jet-IIIM on minimum is pretty good). I do know that some animals are said to only have monocromatic vision, so I guess they only have the rods and no cones in their eyes, I also know that some nature shows include the use of red light at night and they explain that the animals can't see the light they use. That would suggest that red light does not affect the rods in our eyes.

I quite like a red filter on a variable output light - set the light to only as bright as you need it and it shouldn't ruin your night vision. I have the Olight filter and my Ti Infinitum has variable output.


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## entoptics (Aug 18, 2010)

I wonder if a deep purple light would have the same effect as red. It's not as far off in wavelength from "average green" as red, but in theory, it should be off near the edge of the visible spectrum.

Any graphs with violet test lights?


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## DM51 (Aug 18, 2010)

Thread derailed by off topic argument... :green:


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