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Old 22-03-2012, 23:29   #46
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Re: What's it Going to Be ? Red or Green LED Compass Light ?

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Glad to hear it worked out.
See if you can test your night vision with the 2 alternatives to see if the reduced spill from the UV compensates for the loss of red.
I think you will find the UV option better when only partially dark adapted but worse when fully dark adapted.
I will try what you say. This should be interesting. The nice thing about this setup is that I can go from bright red or bright UV to nearly off on both. So as I get night-adapted I can just keep turning them down and down. Then I have a center off position on the switch if I don't want anything on at all. (My previous "off" switch on my other boats has always been..........a towel!)

Thanks...
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Old 22-03-2012, 23:39   #47
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Re: What's it Going to Be ? Red or Green LED Compass Light ?

I thought it related to how the different frequencies close down the pupil for a given level of light with the pupil being the least sensitive to the longest wavelength, red....and the pupil being most sensitive to the shortest visible wavelength, blue/purple.

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Old 22-03-2012, 23:42   #48
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Re: What's it Going to Be ? Red or Green LED Compass Light ?

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A lack of vitamin A can completely destroy night vision, but for the readers of this forum carrots are unlikely to make any difference to night vision.
Aha!! but carrots are the answer

According to that font of all knowledge, Wikipedia (its on the internet so it must be true )

Vitamin A is found naturally in many foods:
liver (beef, pork, chicken, turkey, fish) (6500 μg 722%), including cod liver oil
dandelion greens (5588 IU 112%)[11]
carrot (835 μg 93%)
broccoli leaf (800 μg 89%) According to USDA database broccoli florets have much less.[12]
sweet potato (709 μg 79%)
butter (684 μg 76%)
kale (681 μg 76%)


No. 3......carrots ....which is really choice no.1 because I really can't see anyone quaffing large quantities of cod liver oil or dandelions..

So carrots it is....green ones
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Old 23-03-2012, 00:06   #49
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Re: What's it Going to Be ? Red or Green LED Compass Light ?

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I thought it related to how the different frequencies close down the pupil for a given level of light with the pupil being the least sensitive to the longest wavelength, red....and the pupil being most sensitive to the shortest visible wavelength, blue/purple.

Nice theory, but I am afraid totally wrong. Dark adaption is mostly to do with retinal adaptation. The pupil changes size, but has to trade off aberrations so the size change only makes a small contribution to dark adaption.
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Old 23-03-2012, 15:57   #50
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Re: What's it Going to Be ? Red or Green LED Compass Light ?

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Nice theory, but I am afraid totally wrong. Dark adaption is mostly to do with retinal adaptation. The pupil changes size, but has to trade off aberrations so the size change only makes a small contribution to dark adaption.
I think I also remember reading that even though red has a lesser effect, it also takes a proportionately higher intensity of red for us to make out details with it. So, in the end, the different colors makes no difference because the intensity required for each color ends up evening it out.

IF the compass is constructed out of materials where only the letters and markings reflect UV light, I think it would work. You should be dealing with a high-contrast situation, so the intensity should be able to be very low.

BUT, the red theory sounded good for many years until research finally got around to disproving it. Our UV theory could follow a similar road...

-dan
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