Colour of stairway courtesy lights.

coopec

coopec

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Is it important to have red courtesy lights on the stairs to avoid destroying night vision or is that a myth??
 
A lot depends on how different people adapt to night vision and what instruments you have up in the cockpit.

Some people (especially when younger) adapt enough within seconds from bright to dark to take over or look around. They may not be able to make all the dark shapes for a minute or two but can immediately see the horizon and other boats lights. So doesn't really matter to them.

The other thing I have noticed on some boats is that instruments (including screens) in the cockpit can be much brighter than I would normally have so effectively the real night vision is never quite there. Once again I'm not sure how match that matters out at sea but going into a dim cabin (even with white lights) won't make a big difference.

My early sailing memories on a traditional wooden boat with paraffin lights and no electrics were based around no lights at all apart from a red torch and night vision was sacrosanct but not so sure now.
 
Latest information is that red light is a myth - all that matters is the brightness and the traditional red night lighting worked because it was simply dimmer than the white.

However, regardless of the science, I like red light for night operations and so my chart table lighting has both a knob for brightness and a switch for red or white (two different LED strips inside a milled-out polycarbonate bar). I also have a short length of red LED strip next to the main galley light so that someone can put the kettle on without blinding those on deck. The only white light used for night sailing is yet another LED strip which is mounted just above the chart table and screened in such a way that it produces a gentle wash across the surface of the chart, to remove the colour distortion of red light. This again has a brightness knob that can be turned down to "off" if not wanted.

Not convinced that courtesy lights on the companionway are needed at all for night sailing - you'll be used to the boat and where to hold and step instinctively, and won't need it specifically illuminated. Best to have as little light around as possible if you want good night vision. So maybe fit white ones and expect to use them mostly when not sailing.

Pete
 
prv said:
Latest information is that red light is a myth - all that matters is the brightness and the traditional red night lighting worked because it was simply dimmer than the white.
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No, not a myth. Night vision (scotopic vision) is mediated through rod cells in the retina and is colourless. The cone cells, which give you colour vision, don't function at low light levels. Rods are most sensitive in the blue/green segment of the visible spectrum and are insensitive to red light. Night vision takes time to adapt when moving from a light environment to the dark (5-10 minutes - longer to optimal performance), but is immediately supressed going from dark to light. If you use red light below decks and in cockpit instruments you will not interfere with rod adaptation, and so preserve scotopic sensitivity. If you use white light, your vision will have to dark adapt again every time you return to the cockpit. There may be good reasons to use lights in the cockpit at night, but you can't have optimal night vision and lighting that isn't red.

External lights - buoys, nav lights - are bright enough to be seen with cones, hence you can see their colour. Because of this they will interfere to some degree with dark adaptation.
 
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Thanks guys for your help!

I don't know how people built boats before the advent of the Internet. I buy all my components, fasteners, instruments over the Internet. I work out how to do things (e.g. mount a bilge pump) from information on YBW forums and information from other websites. I suppose, because of the lack of information, there are so many old, disused boats that no-one in their right mind would ever take out to sea.
 
prv said:
I was thinking of this: http://stlplaces.com/night_vision_red_myth/ but I'll freely admit I'm no expert.
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Quote from that page:

If you must see detail (reading a star chart, or instrument settings) and can lose peripheral vision (see note 1), then a very long wavelength red at a very low level. Red really only has an advantage at very low levels (were the night blind spot is very obvious).

It also mentions that we can't focus on red and blue at the same time. I remember the blue studio "Rehearsal" lights at the BBC, they often appeared to have a second filament, presumably caused by the blue filter and the red glow of the actual filament.
 
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Colour of stairway courtesy lights.

Is it important to have red courtesy lights on the stairs to avoid destroying night vision or is that a myth??
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I don't have a 'stairway' on my boat. Starlight suffices, when peeps in the cockpit want to go to the bog. Or, there's another way.....

Simples....
 
prv said:
I was thinking of this: http://stlplaces.com/night_vision_red_myth/ but I'll freely admit I'm no expert.

Pete
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I read this and was puzzled by his claims and the basis for them. Dark adaptation is a two-stage process. Firstly, the cones adapt so that you retain colour vision. Then, when the light level is too low for the cones, the rods continue to adapt. At that point you lose visual acuity and have a very small foveal blind spot. It is only the very centre of the fovea that has no rods, and that rod-free zone is less than 0.5 mm in diameter. The loss of visual acuity arises partly because rods share neurones, so information passed to the brain comes from a cluster of cells rather than a single cone, partly because rods are thinly spread around the fovea, and partly because of diffusion of light through other structures which are absent in the centre of the fovea. It's fair to say that visual detection within a central 10 to 15 degree cone will be very poor.

Rods are not sensitive into the red and infrared spectrum. I've tried to find scholarly articles to support his statement, but failed to do so. Both human and primate research places the cutoff at about 640 nm. There is a small overlap between rod sensitivity and the emission spectrum of red LEDs, but this is an overlap of very low sensitivity with very low emission, so of no practical significance where low level illumination with red LEDs is used.

Using blue/green light at a level bright enough to allow cone (high acuity foveal) vision will reverse rod dark adaptation - obviously, since that is where rods are most sensitive.

Autokinesis is an empty field effect. That is, if there is nothing to fixate on, the eye will make random movements. If a fixed light becomes visible you will fixate on it and there will be no apparent movement. If you see a flashing light you will attempt to fixate on it. When it goes out you will lose fixation and make a saccadic (jerky) eye movement to where your brain thinks the light is. The result is that the flashing light will appear to move. You should be able to demonstrate this to yourself when you spot a distant navigation buoy on a dark and moonless night. The myth here is that "this has probably led to a number of plane crashes". There is a possibility that it might have been a factor in a few aircaft accidents.

In reality, few recreational sailors will operate solely on rod vision. There are usually light sources which are bright enough to be detected by foveal vision. However, it is sensible to keep as well dark adapted as possible. Using dim red lighting allows you to read charts, books and instruments while protecting rod adaptation and also while protecting adaptation of blue cones and most of the adaptation of green cones. (There's considerable overlap in sensitivity of red and green cones, but the spectrum of red LEDs peaks at wavelengths longer than the peak sensitivity of red cones, so the overlap of the shorter wavelength green cones and red LEDs is small)
 
noelex said:
Wow great post Andy.
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Yes, great post.
Thank you.

I was trained that at night to use the 'figure of 8' motion with my eyes when trying to keep a lookout - i.e. the peripheral vision will pick something up whereas looking directly at it, one will not see it. I think this is correct because I often see things at night with my peripheral vision and do not see it when I turn my eyes to look at it.

But then that could just be me with squiffy eyes:)
 
Sailingsaves said:
i.e. the peripheral vision will pick something up whereas looking directly at it, one will not see it. I think this is correct because I often see things at night with my peripheral vision and do not see it when I turn my eyes to look at it.
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Yes, that's correct.
 
Sailingsaves said:
I was trained that at night to use the 'figure of 8' motion with my eyes when trying to keep a lookout - i.e. the peripheral vision will pick something up whereas looking directly at it, one will not see it. I think this is correct because I often see things at night with my peripheral vision and do not see it when I turn my eyes to look at it.

But then that could just be me with squiffy eyes:)
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Don't think it's just you :)

We were taught the same thing in Cadets at school. Also to close the right eye to protect its night vision when a bright light appeared. Always the right eye, so that you could still see through a rifle sight when the dark returned :). I still do that.

Pete
 
prv said:
Don't think it's just you :)

We were taught the same thing in Cadets at school. Also to close the right eye to protect its night vision when a bright light appeared. Always the right eye, so that you could still see through a rifle sight when the dark returned :). I still do that.

Pete
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Unless Of course you are left eye dominant and shoot off the left shoulder! :)
 
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