chart table red light....any suggestions?

[sarabande]

there's some additional material here:-

http://www.astromax.org/activities/members/kniffen.htm

The first paragraph says it all.


This article suggests that pilots prefer green lights in cockpits. Any aircraft types care to comment ? I'm sure the MoD have got buckets of secret research on it !
http://www.equipped.com/nitevision.htm


And this site shows how, when you have adapted to dark, how much less light you need, and how perception of 'reflected' light varies.
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/bright.html


The graph I've attached shows how at low levels the eye is better at using light from the blue end of the visible spectrum than the red.

Can we take it that the use of red light for providing the best ambient light for e/g/ chart tables, is not proven ?

 

[noelex]

The article you dismiss has extensive references but you provide none. Could you point me in an appropriate direction to obtain more information? It would be helpful in particular to know which of the "fundamental properties of vision" you had in mind.

The reason red light is superior at preserving night vision can easily be seen by comparing the Scotopic (these are rods which we use at night) sensitivity curve to the photopic (cones that we use for reading maps) sensitivity curve.
These show our night vision is very insensitive to red. A red light (above 625nm) cannot be seen by our scotopic (night) vision and therefore will not effect our scotopic vision. Notice our photopic vision can still see and use this light.

The photopic and scotopic curves can be seen here
http://en.wikipedia.org/wiki/File:CIE_1951_scotopic_luminosity_function.svg
http://en.wikipedia.org/wiki/Photopic_vision

General dark adaptation information
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html#c5 http://hyperphysics.phy-astr.gsu.edu/hbase/vision/bright.html
http://www.visualexpert.com/Resources/nightvision.html

 

[sarabande]

that Hecht paper is 1987. I hope that there has been an improvement in knowledge over the last 23 years.

I'm going to ferret around a bit more on this with the UKHO.

 

[Graham_Wright]

The use of red light to preserve night vision is not a “fallacy or myth”, but is based on the fundamental properties of vision.

I used to work for Smiths Industries who were the worlds principal supplier of aviation instruments. They were contracted to perform an evaluation of the effectiveness of red light versus dim white light for readability and night vision defence.

The conclusion was that dim white light was preferable.

I assume that for a funded MOD investigation, they were able to call on those with the appropriate credentials.

 

[noelex]

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The graph I've attached shows how at low levels the eye is better at using light from the blue end of the visible spectrum than the red.

I am afraid you are reaching totally the wrong conclusions from the graph.
As you point out he graph shows our scotopic (night) vision is most sensitive to blue. To read a chart we need to use our photopic vision. The ideal is to use a light that will be OK for photopic vision, but not effect our scotopic vision. The graph shows using blue would be the worst choice not the best.
We do not want to use a wavelength light that our night vision is most sensitive to, because this means that light will be the best at bleaching out our night vision.
I think if you look at the graph again you will will see it shows red is best choice.

 

[bbg]

The answer is one of these PETZL headlamps. Small, light, waterproof (to 1 m). Use it on deck and then keep it on to read the chart below. Or hang it by the chart table.

Top tip - keep a headtorch (ideally splashproof or waterproof) as the last thing you put into the grab bag, and the flare container. If you ever need to use either of those things it is nice to know that you won't need to scrabble around for a torch, just open the emergency pack and grab the thing on top.

 

[noelex]

that Hecht paper is 1987. I hope that there has been an improvement in knowledge over the last 23 years.

I'm going to ferret around a bit more on this with the UKHO.

Most of the research on dark adaptation was done around 1930. Once the threshold and increment threshold data was collected there has been little interest in repeating the work. There has been more recent research on military and commercial pilots vision, particularly integrating night vision equipment and detailed radar displays, but this is of little relevance to the average yachtsman who uses, mostly, unaided vision to perceive the outside world.

 

[Csail]

Another tip i learnt when flying is close one eye if using a light at night.

 

[ayearsley]

I always had two Labcraft 8 watt fluorescent tube lights, one red and one white over the galley and chart table so that crew could both navigate and make coffee without disturbing night vision (RN surface and submarine background). Labcraft provided a slip over red tube. I never found that the light on a stalk gave adequate coverage of the chart.

 

[sarabande]

Hi Noelex

rather than get involved in a technical debate and work my way through pages of heavy stuff outwith my direct experience, I've arranged for a response from the UK Hydrographic Office, which is local to me.

I always value professional knowledge, but the conflicting views both here and on the web about red/green/white light and night vision give me concern that there has been a lack of rigour, a reliance on out-of-date practice and hearsay, and some unwillingness to revisit traditional positions. (I exclude yourself from these last comments, as you clearly have professional knowledge.)

As soon as I have a formal reply I will post it, as I am as keen as anyone to ensure that my fading powers of accommodation and adaptation are not hindered by a less than desirable lighting system on board.

It would be encouraging to feel that we may, by robust debate, be providing a small advance in best practice for our chosen area of recreation.

Perhaps as Csail has suggested, we should all be wearing a piratical eye patch when sailing at night.

 

[bbg]

As a merely practical matter, if you are going below to check the chart - with either a red light or white - it makes sense that the last thing you do, while you still have your best night vision, is to take a good long look around the horizon. Identify what is there while you can.

 

[noelex]

Hi Noelex

rather than get involved in a technical debate and work my way through pages of heavy stuff outwith my direct experience, I've arranged for a response from the UK Hydrographic Office, which is local to me.

As the UK Hydrographic Office is concerned with charts. I think you will find they will point out correctly that only white light will provide the colour rendition to read charts completely.(red light will only provide monocromatic vision)
Whether the extra detail provided by white light warrants the reduction in night vision is a more difficult question and will vary with circumstances.
If you at least think about protecting your night vision and consider the consequences before you turn on any light , especially a white light, you will be doing better than many skippers.

 

[alan_d]

The reason red light is superior at preserving night vision can easily be seen by comparing the Scotopic (these are rods which we use at night) sensitivity curve to the photopic (cones that we use for reading maps) sensitivity curve.
These show our night vision is very insensitive to red. A red light (above 625nm) cannot be seen by our scotopic (night) vision and therefore will not effect our scotopic vision. Notice our photopic vision can still see and use this light.

The photopic and scotopic curves can be seen here
http://en.wikipedia.org/wiki/File:CIE_1951_scotopic_luminosity_function.svg
http://en.wikipedia.org/wiki/Photopic_vision

General dark adaptation information
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html#c5 http://hyperphysics.phy-astr.gsu.edu/hbase/vision/bright.html
http://www.visualexpert.com/Resources/nightvision.html

Thanks for that, noelex, a lot to think about there. I may come back to you later ...

 

[john_morris_uk]

The question at the heart of this debate is "what are we trying to see?". When I am on deck at night on my boat I want to be able to see the lights of other boats and ships and I want to be able to move about safely in the ambient light available to me. The instruments are on and I see them clearly with their yellowish dim lighting. If I want to check the sail trim I know I will need to shine a torch. (I don't know anyone who claims to check their sailtrim with their night vision!) Having read through some of the papers that have been cited, it seems to me that my gut conclusion is still right- it's the brightness of the light that us critical for our application. The fact that ships and subs have used red light in the past is irrelevant - I've been on too many bridges (and in too many submarines) where I know the watchkeeper has a mini maglight handy with a shaded lens to see what he or she is actually doing.

Very dim light is the way ahead for me, and I stand by to be shot down in flames...

 

[alan_d]

OK, thinking this through:

Vision in very low light is, for all practical purposes, via the rods (scotopic). Dark adaptation (and its reversal) is complex and involves inter alia both photochemical changes to rhodopsin (visual purple) in the rod cells and neuro-perceptual changes including the number of rod cells treated as a single unit by “higher level processing”. The neuro-perceptual changes are rapid, rhodopsin is bleached from its sensitive to less-sensitive state very quickly, but the reverse effect is the one that takes 30 minutes or so. For our purposes therefore we need only consider what happens to rhodopsin.

If I have understood correctly, the actual photon-detector in the retina is the opsin (rhodopsin in the case of the rod cells), and it is a chemical change to this which initiates the neural activity eventually interpreted as “seeing something”. Consequently, if rod cells have been shown to be insensitive to light at the red end of the spectrum it is a reasonable inference (and may even have been demonstrated) that red light will not bleach rhodopsin which will consequently remain sensitive to low levels of light in the green-blue part of the spectrum.

It would seem to follow that red light, even at high intensity, should not damage one’s dark-adaptation. In practical applications, however, most people seem to think that the intensity of a light is at least as important as colour in retaining or destroying one’s night-vision. I would guess that this is because what we call red light may not be of a single wavelength but is usually white(ish) light which has been passed through a filter which preferentially transmits light around the red frequencies while allowing lesser transmission of other frequencies. Thus as the brightness of a “red” light is increased the brightness of the non-red light it emits increases too, affecting rhodopsin and hence night-vision.

The conclusion I draw is that if a source of pure-spectrum red light were available one could use a sufficiently bright source to be able to see using one’s photopic cells (cones) without impairing the sensitivity of one’s rods to dim blue-green light. Although one would be activating colour-sensitive cone-cells, one’s vision would still be monochrome because only red light would be there to be seen. There seems to be no way of achieving colour vision while retaining dark-adaptation (except by using alternate eyes).

In the real word, where red lights are actually polychromatic but with red predominating, the best chance of retaining night vision is to use a red light at as low an intensity as possible. If you need to see colours you will have to use white light and accept that this will impair your night vision, and that impairment will be less the dimmer the light.

How pure is the spectrum from red LEDs?

 

[Boathook]

this red light preserving night vision business is a fallacy.

All you need is a very dim white light.

In red light, it is very difficult for the eye to perceive detailed print.


http://stlplaces.com/night_vision_red_myth/

Totaly agree about the red light. Much better to use a smaller wattage clear bulb. another good idea is not to loook directly at the light bulb when in use. PBO in the sketch book section suggested using an eye patch to keep a good 'night eye'. Haven't purchased an eye patch yet .....

 

[noelex]

OK, thinking this through:

Vision in very low light is, for all practical purposes, via the rods (scotopic). Dark adaptation (and its reversal) is complex and involves inter alia both photochemical changes to rhodopsin (visual purple) in the rod cells and neuro-perceptual changes including the number of rod cells treated as a single unit by “higher level processing”. The neuro-perceptual changes are rapid, rhodopsin is bleached from its sensitive to less-sensitive state very quickly, but the reverse effect is the one that takes 30 minutes or so. For our purposes therefore we need only consider what happens to rhodopsin.

If I have understood correctly, the actual photon-detector in the retina is the opsin (rhodopsin in the case of the rod cells), and it is a chemical change to this which initiates the neural activity eventually interpreted as “seeing something”. Consequently, if rod cells have been shown to be insensitive to light at the red end of the spectrum it is a reasonable inference (and may even have been demonstrated) that red light will not bleach rhodopsin which will consequently remain sensitive to low levels of light in the green-blue part of the spectrum.

It would seem to follow that red light, even at high intensity, should not damage one’s dark-adaptation. In practical applications, however, most people seem to think that the intensity of a light is at least as important as colour in retaining or destroying one’s night-vision. I would guess that this is because what we call red light may not be of a single wavelength but is usually white(ish) light which has been passed through a filter which preferentially transmits light around the red frequencies while allowing lesser transmission of other frequencies. Thus as the brightness of a “red” light is increased the brightness of the non-red light it emits increases too, affecting rhodopsin and hence night-vision.

The conclusion I draw is that if a source of pure-spectrum red light were available one could use a sufficiently bright source to be able to see using one’s photopic cells (cones) without impairing the sensitivity of one’s rods to dim blue-green light. Although one would be activating colour-sensitive cone-cells, one’s vision would still be monochrome because only red light would be there to be seen. There seems to be no way of achieving colour vision while retaining dark-adaptation (except by using alternate eyes).

In the real word, where red lights are actually polychromatic but with red predominating, the best chance of retaining night vision is to use a red light at as low an intensity as possible. If you need to see colours you will have to use white light and accept that this will impair your night vision, and that impairment will be less the dimmer the light.

How pure is the spectrum from red LEDs?

Alan that’s a great description. If you have deduced that, without formal education in the subject that is wonderful and very perceptive.
Your comments on the need to achieve reasonably pure long wavelength light to gain most of the advantages is particularly astute.
Relatively recent technology in the form of monochromatic LEDs that achieve this desired long wavelength red light has made it much easier to have this type of lighting
.
Car drivers and pilots are now operating in an increasing brightly lit world. Yachtsmen are one of last remaining groups that truly use their scotpic vision and benefit from using illumination that will preserve this low illumination vision. Its a pity information presented on the internet is confusing, but Alan ,you, give me some hope that the message is understood.

 

[Mandarin331]

For a good cheap light try a LED bike rear lamp. Uses 2 x AA batteries and easy to install. Batteries last for ages.

 

[sarabande]

I've had correspondence with the UKHO this morning. A somewhat unsatisfactory answer at the end of which this message was added.

"The contents of this e-mail and any attachments are the property of the United Kingdom Hydrographic Office and are intended for the confidential use of the named recipient only. Its unauthorised use, disclosure, storage or copying is not permitted and may be unlawful."


So I can't tell you the lots and lots of interesting stuff I have found out especially about restricted wavelength LEDs, blah, blah, otherwise I'd be taken off to the Tower again.

Needless to say, battle to get the full story from the Mount has been joined....

 

[pampas]

Personally I have found that Orange lights are the best, my last boat had this colour fitted not only for chart work but seconary cabin lights, So pleasing to the eye that I used to use them most of the time. The fittings came from low voltage systems one sees in warden controlled accomodation alarm boxes.

Just another slant on what one prefers.