"Stan Gosnell" wrote in message
...
"Jay Beckman" wrote in
news:CKRxd.11974$ry.7550@fed1read01:

What do you find superior about green instead of red light?


some stuff snipped

The human eye is much more sensitive tou green light than red
light.

I need to preserve my night vision to some extent, because I'm
not always landing to a brightly lit runway.

I prefer narrow-band sources,
and red is the least effective of all the colors.


There are two issues here, and Stan (the other Stan) has touched on both.
One is simply vision within the cockpit, and for this, any color of light
will do, except that the color should not compromise readability of
instruments and charts. Red is not the best choice for this. The other
issue is vision outside the cockpit, which is still very important for IFR
flight, as Stan pointed out. Light color and intensity should be chosen to
allow good in-cockpit visibility without compromising outside visibility.

The physiological basis for night vision (dark-adapted, or scotopic vision)
is primarily the characteristics of the retinal photoreceptors called rods.
These are indeed more sensitive to shorter wavelengths, and, at low
illumination levels, less light intensity should be required if a green
light is used. But true dark adaption is based on the presence of a
light-sensitive pigment in the rods called rhodopsin. This pigment is
naturally synthesized in the rods but is destroyed by light. Dark adaption
is the process of allowing the concentration of rhodopsin to increase by not
allowing its destruction by light. It takes 45 minutes or so for it to
reach maximum levels, but can be destroyed by a few seconds of exposure to
higher light levels. Red light does not have the destructive power on
rhodopsin that shorter wavelengths have, and that is why red light has long
been favored when maximum preservation of night vision is required. Blue
and green will have a stronger destructive effect.

The cones also become somewhat dark-adapted using other pigments, and they
respond much more quickly, like 5-7 minutes.

However, a balance must be struck. I think that most of our aviation vision
occurs in the so-called mesopic region, in which both rods and cones
contribute significantly. Dim white light or light of other colors will
allow good readability of instruments and charts while allowing reasonable
dark adaptation. The main thing is to avoid bright light.

My own experience is that red works well for me except on sectionals. Some
of the red lamps I use are a little brighter than I would like but I don't
find that they mess up my adaption even when falling directly on my face
briefly. White light does mess me up unless it is very dim. I haven't used
other colors. I keep a little white Photon microlight handy for looking at
sectionals when needed, but it does mess up my vision because it is so
bright.

One good reference is "Night Vision In Military Aviation", by the USAF
School of Aerospace Medicine:

http://www.brooks.af.mil/web/af/cour...tures/UNV7.doc


Stan