RE: [Paddlewise] compass and red light

 

Mark Zen wrote ---

> last time [night vision] came up, someone provided a reference to a "reliable source"
> saying this wasn't true [the red light] although we used it on our ships in
> 1990, i can't say what they use now, mainly cause i got out in '90, and moved
> 2000 miles from the nearest ocean ;-)
> 
For Mark and Chuck, anyway, last time I flew Navy aircraft, we had 
red filters on all the candles on and in the instrument cluster; later, 
when we converted to coal oil lamps, we stayed with red.  In the 
meanwhile, the Navy went to dim white light in aircraft --- can't 
imagine your ships changing, Mark: y'know, "224 years of tradition, 
unhampered by progress --- the United States Navy!   It was easier 
to see than white, and was easier for the relatively senior guys to 
see <anything> at night!  (To this day, I hate renting anything by 
Pontiac --- can't see a bloody thing on those red panels at night!)

Anyway, now we're all into pale green cockpit lighting for 
compatibility with night vision goggles (NVGs) on all tactical 
aircraft.  A red light in an NVG is instant bloom and loss of vision 
for the time being --- a bad thing, especially on final to a carrier on 
a dark and stormy night.

I know I promised more analysis from Pax River, Chuck, and I'll try 
to get the definitive word on that tomorrow.

Jack Martin


Jack, Mark and Chuck, et al,
  I have been doing more research on this.  One aspect of this seems to be a divergence of opinions between the ground and the surface and air components.  No surprise there huh?  What I have found is that red light does not stimulate the rods of the eye, (as long as light transmitted below 650 nm is eliminated).  This in turn lets the rods adapt to the dark.  As near as I can discover this does not affect the cones, they need plain old dark to adapt to the dark.  This should not be important since, in my understanding the cones are incapable of operating in star light.  I could easily be wrong on this part however.

  It is also worth mentioning that it takes around 30 minutes for the rods to adjust to the dark.  Also, each eye adjusts independently, so if you do need to expose a bright light, closing one eye will maintain your night vision in that eye.

  Another factor in our environment is daylight exposure to bright light.  4-5 hours of exposure to bright daylight can delay the acquisition of night vision by ten minutes or more, as well as lowering the final level.  After a week or two, (again I am fuzzy here) the cumulative effect of this can be up to a 50% reduction in night vision.  The jist - wear sunglasses and a brimmed hat in the sun.

  Blue or blue green lights are used in many cockpits in which the pilots will be using third generations NVDs.  The new NVDs are not sensitive to light in this part of the spectrum, the human eye is however.  In addition, blue light is best for near vision.
If you are using the latest generation of night vision devices, then you might want to go with blue light.

  Another thing to bear in mind is the part of the eye used to view objects at night.  The center part of the eye is used to identify objects, the outside of the eye is used for spatial orientation and motion detection.  Therefore it is often easier to see in the dark by looking out the side of your eye, or on the periphery of your vision, rather than looking directly at whatever it is you are trying to see.

  I'll conclude this now, it is already long enough.  As always this is only going to be part of the answer, to part of the question.  By the way, what was the question?

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