# Whats the limit on white light for saving night vision?



## fire-stick (Sep 1, 2006)

At what level does white light start to ruin night vision?
I know my Dorcy AAA 1xLED kills my night vision. (both old and new version)

At what level does red light start to ruin night vision.
My army light with red and diffuser filter (and pretty much dead batteries) doesn't hurt my night vision all that bad. (from what I remember)


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## TinderBox (UK) (Sep 1, 2006)

Keep one I shut when you use your flashlight. :lolsign:

to preserve the night vision in that eye.

regards.


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## fire-stick (Sep 1, 2006)

LOL... I tried it... It didn't work.. 


Maybe if I had a very bad case of Anisocoria covering one eye would retain night vision in that eye....
http://en.wikipedia.org/wiki/Anisocoria


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## Planterz (Sep 1, 2006)

Your vision relies on photoreceptive chemicals (called photopsins) in your eyes. The photopsins in the cones in your eyes detect colors, and the photopsin (called rhodopsin) in the rods detect amount of light (black and white). Rhodopsin is what gives you "night vision" and is slow to build up and easy to destroy. This is why it takes a good half hour or hour (or longer) to build up "night vision" and why it's ruined so easily. It's also why when you look at a bright light you see spots in the middle of your vision.

Rhodopsin is increasingly minimally sensitive when you hit the "red" part of the spectrum. However, the cones still pick up red fine, so you can still see by red light, even though the rods aren't detecting much of anything. The deeper red you go (towards 700nm) the less your night vision will be damaged, but it's harder to see. The one problem with relying on red for vision at night is that cones are on the outiside of the responsive area of your eye, while the rods are at the center. This means you can have "blind spots" in the middle of your vision when using only red light, which could make it hard to do precise vision work (like reading).

The difference between the photopsins in the cones and the rhodopsin in the rods is that the photopsins in the cones are much less sensitive and quicker to build up than rhodopsin. So it's perfectly possible to "blind" yourself with a bright red light (you'll see red spots), but the recovery time is much quicker than with a white light. This doesn't quite follow as much for other colors, as the rhodopsin is more sensitive to shorter wavelength light than red, thus if you shine yourself with a bright green light, you'll be destroying both the cone's photopsins and the rod's rhodopsin.

Back to white light, rods, rhodopsin, and night vision, it takes very little white light to be able to see with night-adapted vision. If you need to read a road map or something (difficult to do with red-only light, especially when red is a common color on such maps), use the dimmest amount of white light possible. It also helps to have the light widely diffused (spread out) and not focused into a small spot.


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## abvidledUK (Sep 1, 2006)

TinderBox (UK) said:


> Keep one I shut when you use your flashlight.
> to preserve the night vision in that eye.



It only works if you keep both eyes shut !!


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## jayflash (Sep 1, 2006)

The 0.3 lumen setting on my HDS U60 does the trick maintaining my rods.


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## D MacAlpine (Sep 1, 2006)

Planterz said:


> ... The one problem with relying on red for vision at night is that cones are on the outiside of the responsive area of your eye, while the rods are at the center. This means you can have "blind spots" in the middle of your vision when using only red light, which could make it hard to do precise vision work (like reading).....


 
I thought that the cones were concentrated in the middle of your retina (fovea centralis?) and more densely packed. This explains why at night you can sometimes see things better by looking off to one side of them so that you are using the rods in your eyes. Also why things can look "grainier" in the dark, your resolution has been lowered.

Everything else Planterz said is exactly as I understood it. I'm no medical expert, can anyone definitively settle this one?

Don


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## stoven (Sep 1, 2006)

Just buy an NVG light. The Infinity Ultra NVG from Gerber uses a special filter that gives off a light that gives full color rendering but does not affect night vision. It's much better than using a red LED.


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## C4LED (Sep 1, 2006)

A white CMG LED Infinity Task Light isn't bad - quite dim and lasts for 40 hours.

However, a 5 mm dim red led works the best. I've got a red AAA Peak prototype that does a great job of preserving night vision. Another brighter red light I use is the Nite Ize 3 LED placed in a Mini Mag. It works well, and is a lot brighter, still preserves the night vision, though not as well as the Peak. The red Nite Ize still allows for retention of most night vision.


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## Planterz (Sep 1, 2006)

D MacAlpine said:


> I thought that the cones were concentrated in the middle of your retina (fovea centralis?) and more densely packed. This explains why at night you can sometimes see things better by looking off to one side of them so that you are using the rods in your eyes. Also why things can look "grainier" in the dark, your resolution has been lowered.


You're right, I got that backwards.


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## joema (Sep 1, 2006)

fire-stick said:


> At what level does white light start to ruin night vision?...


I've experimented with this using my HDS U60 during astronomy "star parties". In general the lowest level (0.08 lumens) doesn't affect night vision. As you get brighter, there's more effect. There's not a single value and the situation is very fluid -- reflect the light off a mirror into your eye and it hurts night vision more than reflecting off a dark surface.

Night vision is gradually acquired according to a curve. You get a fair amount of adaptation within a few minutes, but sensitivity continues increasing for 30 minutes or more:

http://www.visualexpert.com/Resources/nightvision.html
http://web.utk.edu/~wverplan/biblio10.html


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## Sub_Umbra (Sep 1, 2006)

fire-stick said:


> At what level does white light start to ruin night vision?


Since most of what we call Dark Adapted vision is actually _mesopic_ vision, (a combonation of scotopic and photopic vision) you CAN use just enough white light so that your rhodipsin will be replaced as fast as you burn it up. This would probably be at a different level of intensity for each person.


stoven said:


> Just buy an NVG light. The Infinity Ultra NVG from Gerber uses a special filter that gives off a light that gives full color rendering but does not affect night vision. It's much better than using a red LED.


Are you sure? The Phantom Warrior has a white beam that has the IR filtered out so that it doesn't effect _Night Vision *Devices*_ but I find it hard to believe that you can look at wavelengths of light of known rod sensitivity that won't desensitize rods. Got links?


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## jar3ds (Sep 22, 2006)

from my personal experience.... even a really floody white light that is really dim will still cause me to lose night vision... 

the only light that doesn't make me squint and such is a RED light...


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## Sub_Umbra (Sep 22, 2006)

> ...even a really floody white light that is really dim will still cause me to lose night vision...


Floody lights will always take _more_ of a hit on dark adapted vision -- all rod sensitivity is peripheral so any kind of floody beam will tend to damage _more of it at once._

A tight beam of variable output (even white) will have much less negative impact on dark adapted eyes if it is turned down low enough.


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