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 om...
"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.