Re: [Paddlewise] compass and red light

Stephen Bird wrote:

> On Tue, 2 Mar 1999 11:24:49 -0600, Chuck wrote:
>
> >>At night the only color that will not damage your night vision is
> >>red. The yellow and green cyalume lights will ruin your night vision
> >>completely.  Red has no effect.
>
> >I've heard it said lately that the color of the light is not so
> >important as its intensity -- that a dim white light will not harm
> >night vision more than a dim red light. I have also seen references
> >to the military using green lighting to protect night vision.
>
> I've also heard it said that the red light theory was a hoax developed by
> the Brits to annoy/distract the enemy during WWII and that there is no
> basis for red being any better than any other colour of the same intensity.

A friend of mine is a professor of optometry and is very interested in
astronomy and has done extensive research on radiation effects
on the eyes.  I've discussed this stuff with him often.  Dim red light
does preserve dark adaptation.  Bright red light can reduce it.  Dim
light of other colors can help preserve dark adaptation, but bright
light of other colors will zap it quickly.

Kayaking at night in a wilderness or open water environment would
certainly benefit from dark adaptation.  Night paddling in urban
regions would not.  One exposure to bright light can require ten
to twenty minutes to recover full dark adaptation.

A farce is the use of red lights in automobile dashboards.  These
provide no benefits at all.  You never dark adapt when driving;
there are simply too many bright light sources that you'll be
exposed to (like the reflected light of your own headlights).
As someone else pointed out, as you age, your ability to see
dim red light is reduced and older drivers are at a disadvantage
(my friend drives an Audi and _hates_ the red night illumination
for that very reason - so much for ergonomics in the auto industry).
The use of red lights for older paddlers using charts and compasses
should be given consideration in light of this.  If it works for
you, use it , if not, consider a dim light of other color.  There's no
point on fixating on the importance of red lights if it means that
you  can't work effectively.

You can tell if you are reaching complete dark adaptation rather
easily.  If it's a clear night, watch the sky.  At first, the sky looks
like stars on a black background.  After a while, the background
will appear to gray and you'll get the impression that the sky is
getting hazy.  In fact, this is a consequence of your retina becoming
saturated with the chemicals that cause dark adaptation.

Hope this helps,
Mike



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