Night vision - a red warning ?

sarabande

sarabande

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I came across this page which provides some food for thoight.

red light area

Any experts out there with views on the effects of red "night vision" lights on:

a) charts
b) screens

What effect does red light really have on visual performance ?

thanks
S.
 
[ QUOTE ]
It takes a while for true night vision to be recovered. About 10 minutes for 10%, 30-45 minutes for 80%, the rest may take hours, days, or a week

[/ QUOTE ]
It does take a short while to regain night vision after being at the chart table with a bright red light (or night mode computer nav screen) .. for 10% though true night vision might take days or a week?! Well - they better go into a darkened room during the day then...
 
It didn't answer any questions for me, either. And it raised one....why is traffic light green the exact colour it is?

Night vision i.e. the ability to actually see a light, is seldom a problem for me - my eyes seem to recover pretty quickly and the biggest problems I have are distinguishing lights ashore from those at sea and distinguishing between near and distant lights. Many is the time I have seen a dim and presumably distant light fine on the bow rapidly become a light belonging to a small vessel nearby.
 
There was an article sometime ago in PBO/YM which pointed out the difficulty reading a standard admiralty chart under red light.

On a personal note, I have never understood the fixation with red lighting that people have and have no special 'red lights' on our boat at all. I believe that the red light thing is a complete myth and that the level of lighting is far more important. In other words much of the so called benefit of 'red lighting' appears to come from the fact that it's 'dim lighting'.
 
No it's not a myth.
The eye has two types of receptors:
1 cones, at the centre of the retina which distinguish colours and shapes at high light levels
2 rods, towards the periphery of the retina which distinguish colours and shapes at very low light levels.
The rods are much less sensitive to red light than are the cones so once the eye is fully dark adapted (after about 30 minutes) and rod vision predominates the rod sensitivity will be much less reduced in in the presence of red light than in blue light.
Putting it simply red light does not "spoil" night vision as much as blue/green/white light does.
Red light is therefore used in military vehcles, ships and submarines in situations where preservation of dark adaption is essential.
 
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No it's not a myth.
The eye has two types of receptors:
1 cones, at the centre of the retina which distinguish colours and shapes at high light levels
2 rods, towards the periphery of the retina which distinguish colours and shapes at very low light levels.
The rods are much less sensitive to red light than are the cones so once the eye is fully dark adapted (after about 30 minutes) and rod vision predominates the rod sensitivity will be much less reduced in in the presence of red light than in blue light.
Putting it simply red light does not "spoil" night vision as much as blue/green/white light does.
Red light is therefore used in military vehcles, ships and submarines in situations where preservation of dark adaption is essential.

[/ QUOTE ]I am well aware of the red lighting used in military vehicles and in submarines. I have been in a few of both! I am also aware of the theory that you outline. However did you read the article referred to in the orginla post? It correlates with my personal experience.

Before I read the article I believed that red lighting as an aid to night vision maintenance was a myth. Having read the article, it reinforced what I believed to be true in the first place.
 
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No it's not a myth.

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Oh yes it is!
A funded, scientific investigation carried out by Smiths Industries (now Smiths Aerospace) showed that dim white light was the preferred illuminant in aircraft. Whether there is any difference between night adaptation short term (head down, head up in fighter aircraft) and longer term such as in chart reading and then going topside on a boat, I don't know. In all my submarine trips, red ruled but then that's the Navy!
 
Interesting - I've always used dim white or, more accurately, the orangy-white of an underpowered tungsten bulb. It is better than the blue-ish light from my new LED miners' head light (which I usually wear at sea at night). Must go back to my old tungsten head light, I suppose.
 
Red light is the best background light to preserve dark adaptation but the eye is more sensitive to green or white light.
Yes you may be able to read a chart with a dimmer green or white light than a red light but you will loose dark adaptation and when you go up to the cockpit to look at the real world you will not be able to see as well as if you had used a red light down below.
I think confusion arises from the oft repeated statement that red light is "best" at low light levels - the argument is more subtle than that.
 
Something else to consider is that our eyes are better at resolving things illuminated with longer wavelengths (i.e. red is better than blue).

This was demonstrated to us at school by having a pair of blue bulbs spaced 5cm apart, and a pair of red bulbs at the same distance apart. You could see two seperate red bulbs at a far greater distance from the experiment that the blue bulbs.

This would therefore suggest that your eyes may be able to resolve a scene with a far lower level of red light than with any other colour (including white). The arguments become a lot less clear cut as soon as you want to look at anything IN colour e.g. a chart!
 
I use dim white lights on my boat, and have experienced no problems. In airline flying, we use white lights (including dimmable spotlights and 'area' lights). The only 'rule' is to go to a 'dark mode' (that is, dim all the lights to minimum usable level or so) prior to take-off or landing. Other than that, it gives few problems. In the cruise at night, we may have bright flight deck floodlighting on some of the time. Note that this is a very different situation to that enjoyed by our military cousins, as we rely upon ATC and systems such as TCAS to avoid other traffic - we don't necessarily keep a stringent look-out...
 
All ships I've sailed on have had serious dimmers fitted to the white chart lights .. such that you can turn them down to zero at extreme. We did not have Red lights. Reason is the charts and red lighting losing various details.

BUT interestingly one publication that does cater for Red Lighting is the International Signals Code book - the green pages are green for that very reason .. and are the Medical pages. Some I heard reckoned green because of the green colour of surgeons gowns ... Nope ... it is best colour to have under red light ........... so I was informed as a Deck Cadet many years ago !!

An old trick ... if you can stand the risk of climbing in / out of cabin with it ... close one eye while in the light ... open it again when back out in dark.
My trick was to squint the eyes - literally look through just a slit of eyelid ... when in lighted area. Reduce amount of light coming in.
 
My trick is to close both eyes before going in a low light situation. That is, close eyes - turn light off - open eyes. I was sure that this was purely psychological, but, then I gave it more thought and concluded that when the eyes open, the signal-recognition centre of the brain goes full speed so it is faster at adaptation. Another "experiment" came to second that.

Looking at the ceiling fan over my bed I couldn't see the blades moving (50 - 100 Hz, I don't know). But if I closed my eyes and opened them again, for a split second I could see the blades still! So my theory is that when we open our eyes, the signal recognition centre goes full speed, constructs the image and then it goes at power-saving mode noticing only the changes.

This of course is my (probably idiotic and naive) theory, but it explains some phenomena to me.
 
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