Night Vision

[Homer J. Simpson]

I was just at the sportys website looking for one of those mini red LED
lights. One of the sidebars claims that,

> "These keychain flashlights emit a bright red beam or a bright white beam that illuminates well,

yet does not affect night vision."



I've been taught that white light destroys your night vision. Is this
claim true?

Joe

[Bob Gardner]

AIM 8-1-6(b) contains information more recent than what you were taught.

Bob Gardner

"Homer J. Simpson" > wrote in message
...
> I was just at the sportys website looking for one of those mini red LED
> lights. One of the sidebars claims that,
>
> > "These keychain flashlights emit a bright red beam or a bright white
beam that illuminates well,
>
> yet does not affect night vision."
>
>
>
> I've been taught that white light destroys your night vision. Is this
> claim true?
>
> Joe
>

[Ron Natalie]

"Homer J. Simpson" > wrote in message ...

> I've been taught that white light destroys your night vision. Is this
> claim true?

The major issue is INTENSITY. Keeping the light intensity down is
the key. While given the same intensity, red will hinder your night
vision less, you actually may bet away with dimmer illumination using
another color.

I actually find very dim white light to work fine. The back lighting on my
Garmin 195 actually makes a quite suitable light to read the charts by.

The military went with green because it interferes with their night vision
hardware less, but some research points out your acuity is better with
green light, meaning you can set it dimmer than you could with a red
light.

[Roger Hamlett]

"Homer J. Simpson" > wrote in message
...
> I was just at the sportys website looking for one of those mini red LED
> lights. One of the sidebars claims that,
>
> > "These keychain flashlights emit a bright red beam or a bright white
beam that illuminates well,
>
> yet does not affect night vision."
>
>
>
> I've been taught that white light destroys your night vision. Is this
> claim true?
A 'bright red beam', will still hinder your night vision...
The 'point' about red, is that (relative to other light colours), it can be
used _slightly_ brighter, without destroying the adaption. However green is
the colour that the dark adapted eye, is most sensitive to. So for a given
'amount' of light, green gives the best 'vision', but red damages the
adaption least.
99% of red lights are still too bright.
As an example of just how dim a light needs to be, think in terms of
computer screen, dimmed as far as it will go, with the sides shielded (to
catch the 'stray' light that tends to leak out the sides), and then covered
with two sheets of dark red acetate.
These keychain lights, work if shone through the fingers, and aimed away
from the eyes.
I think a lot of people who market this type of light, have no idea just how
sensitive a properly dark adjusted eye can be. It is when you are standing
outside at night, and see a cigarette being lit a mile away as an
uncomfortably bright flash, and can see the ground details, and shadows from
starlight (not Moonlight, which is bright enough to destroy good night
vision), that you get an idea of the maximum sensitivity achievable...

Best Wishes

[Dean Wilkinson]

This is a good answer Ron..

Your eyes operate in the photopic mode in daylight (cone vision) and
scotopic mode for night vision (rod vision). Your cones provide color
vision and your rods provide monochrome vision. The peak sensitivity
of photopic vision is right around 555nm (green), but scotopic vision
has its peak sensitivity at around 580nm (yellow).

The important thing is that the light level you use is low enough to
avoid desensitizing your retina to dim exterior light in the real
world. Exposure to light at too great of an intensity will consume
rhodopsin and spoil your night vision. It can take up to 1/2 hour to
become completely dark adapted. Since you rely primarily on your rods
at night, red light does not hold any particular advantage because it
affects your rods. In actuality, blue light might be a better choice
because it will primarily excite your blue cones without affecting
your rods as much...

Another thing to keep in mind at night is the importance of using
averted vision. Because your cones are concentrated in your fovea
(center of vision) and you have very few rods there, you can't see dim
objects if you look directly at them. Looking slightly away from them
will take advantage of the higher rod density away from your fovea and
allow you to see dim objects. You can try this by looking at dim
stars in the night sky and you will see what I mean.

Dean Wilkinson


"Ron Natalie" > wrote in message >...
> "Homer J. Simpson" > wrote in message ...
>
> > I've been taught that white light destroys your night vision. Is this
> > claim true?
>
> The major issue is INTENSITY. Keeping the light intensity down is
> the key. While given the same intensity, red will hinder your night
> vision less, you actually may bet away with dimmer illumination using
> another color.
>
> I actually find very dim white light to work fine. The back lighting on my
> Garmin 195 actually makes a quite suitable light to read the charts by.
>
> The military went with green because it interferes with their night vision
> hardware less, but some research points out your acuity is better with
> green light, meaning you can set it dimmer than you could with a red
> light.

[Don Tuite]

What does taxiing with a landing light do to night vision? What about
flying over a city?

Don

[EDR]

Dean has some very good responses.
I attended the "Into the Darkness: Unaided Night Vision" seminar at the
November AOPA Convention in Philadelphia. Presenter was Andy Engle, OD,
Captain, Medical Service Corp, US Navy, Refractive Surgery Clinic.

An announcement was made at the beginning of the program, "If you do
not intend to stay for the entire one-hour program, leave now. The
doors will be closed and no entry or exit will be permited."
All the door edges were taped and papered to seal out extraneous light.

When the doors were closed, the lights were turned off.
The presenter used a computer slideshow with colors and intensity
selected so not to destroy the viewers dark vision.
The first slide, he told us, was a photo of (something or other, I
don't recall) on a black background.
He told us not to worry if we didn't see it, we would be able to at the
end of the program. I wish he had had a handout, the program was that
good.
As the program continued, and ones eyes adapted, one could actually
begin to see the other people an objects in the room. At the end, the
first slide was again shown and, indeed, the object he at told us would
be there was faintly visible.

This program was based on one that is given to Naval Aviators.

[Thomas Borchert]

Bob,

while we're at it, maybe a question from a friend: Consider a flight in
night IMC. Why would there be any desire to keep the night vision good?
There's nothing to see outside anyway, except for bright runway lights.
Why not make the cockpit as bright as possible?

--
Thomas Borchert (EDDH)

[Newps]

Don Tuite wrote:

> What does taxiing with a landing light do to night vision?

Nothing.

What about
> flying over a city?

Nothing.

[Ron Natalie]

"Newps" > wrote in message news:S0VKb.767486$Tr4.2204802@attbi_s03...
>
>
> Don Tuite wrote:
>
> > What does taxiing with a landing light do to night vision?
>
> Nothing.
>
Doesn't do anything for your night vision, but when you blast the
other plane on the taxiway with your light it destroys his!

About the only other outside-the-cockpit light that was problematic
was when the tower turns up the Dulles runway lights into the
penetrate the fog mode on a clear dark night. The normal illumination
level is actually less than the lighting on the airport service road.

[G.R. Patterson III]

Ron Natalie wrote:
>
> Doesn't do anything for your night vision, but when you blast the
> other plane on the taxiway with your light it destroys his!

But you can do a much better job of this with your strobe lights!

George Patterson
Great discoveries are not announced with "Eureka!". What's usually said is
"Hummmmm... That's interesting...."

[Teacherjh]

>>
Consider a flight in
night IMC. Why would there be any
desire to keep the night vision good?
There's nothing to see outside anyway
<<

Until you break out unexpectedly. There's aluminum out there and it's not
separated from you once you are out of the soup. Without good night vision you
might not even notice you're now in 5 miles in haze over a layer.

Jose

--
(for Email, make the obvious changes in my address)

[Thomas Borchert]

Teacherjh,

Thanks, that's what I said, too: You'll still need to visually scan for
traffic if it's anywhere near marginal VMC. And that's often the case.

--
Thomas Borchert (EDDH)