Colour of Light for Best Night Vision

[Lars_L]

Red light has been used during night on boats for a very long time because it dose not ruins the night vision. It’s well documented that it works. It could be that even Columbus used glow from the wood. I don’t know. It has a drawback. The eyes have a very low dark sensitivity at red light.

I have seen somewhere that green light nor would ruin the night vision. I did a test last night in may boat. In the salon I have a green-LED just for indicate that a relay are activated. In the light from the LED I could orientate may self. I could se my hand, I could even se my fingers, but I couldn’t se my fingerprints. The eyes are quite dark sensitive for green.

My question is, way haven’t we changed the colour of our night-lights?

[bill352]

The aviation industry changed a while ago. As best as I remember, they settled on a dim blue-green for night use.

[Submariner726]

In Submarines we used red for a long time (Rig for Red). As I was getting ready to retire they were changing over to blue seemed to be coming into play.

[noelex 77]

If you want to preserve night vision and you should, the first requirement is the light must be very dim.
Red light is by far the best at preserving night vision, there is no question, no doubt. If you look at the eyes physiology it has to be the best colour.

It does however create problems such as the complete loss of colour information. For many sophisticated military and aviation displays the display information is more critical than preserving night vision.

For the average sailor if looking at simple displays of speed and depth, or tasks such as making a coffee very dim red is the best choice. Think about turning off the chart plotter you will be amazed what you see when your eyes are well dark adapted. This will take about 20 mins.
Often its worth sacrificing night vision to use devices like radar and AIS, but always consider if the "cost" to your night vision is worth the extra information.
A trick worth using sometimes is to keep one eye closed when using the chartplotter and preserving dark adaptation in the other. Or keep one crew member with good dark adaptation. Often coming into an anchorage at night my wife is careful to preserve her night vision and I use the radar etc

[Deadcat7382]

As someone with 20+ years with NVG's and working with lowlight conditions, the blue green currently in use is so much better then the red light used before, to best preserve your night vision, try not to look at lights with your dominant eye, save that for looking out at whats in front of you. IMHO.

[Rhapsody-NS27]

This thread gets me thinking on a couple things. The military once issued me a flashlight that had a green light on it. It works pretty good. I still have it and use it once in a while. It also has an IR strobe too.
I've seen a set of NVGs once while on night watch in Afghanistan that had an Amber filter instead of green. The Amber had a much clearer image. I don't remember it ever effecting my night vision too poorly. I've been looking for another since.

[Lars_L]

Noelex77. You say that red light is the far best at preserving night vision. I can’t se way it should be obvious, but that’s out of my knowledge area, so I believe you. But you also say that light should be very dim. According to the diagram, the eyes have a very low senility in red (zero). To compensate that, you have to go up in intensity.

The eyes have its top sensitivity in blue-green (500 nm) and therefore your able dim it much more. Do that not compensate for the lack of preserving night vision?

[GordMay]

Extremely dim light of any colour will preserve night vision (scotopic vision), since that what night vision is for - for seeing in extremely dim light. At these EXTREMELY dim levels, blue-green is the light wavelength we are most sensitive to, and therefore can be used at lower intensity levels than any other extremely dim colour.

Red light preserves night vision, at a higher intensity level than any other colour, since the dim light elements of the eye (rods) are insensitive to red light. This allows you to operate more effectively with red light, as a result of the greater light intensity possible, and therefore more detailed perception of the environment by the red-sensitive elements, of the eye without disrupting your night adaptation.

See also these very important articles:

The Eye and Night Vision
➥ The Eye and Night Vision | American Optometric Association

Night Vision: The Red Myth
➥ Night Vision - The Red Myth

Green or Red for Better Night Vision?
➥ EQUIPPED TO SURVIVE (tm) - Green or Red for Better Night Vision?

[noelex 77]

Originally Posted by Lars_L

Noelex77. You say that red light is the far best at preserving night vision. I can’t se way it should be obvious, but that’s out of my knowledge area, so I believe you. But you also say that light should be very dim. According to the diagram, the eyes have a very low senility in red (zero). To compensate that, you have to go up in intensity.

The eyes have its top sensitivity in blue-green (500 nm) and therefore your able dim it much more. Do that not compensate for the lack of preserving night vision?

To clarify I would have more correctly said the red light should look very dim to preserve our night vision. the light will look very dim, but as you correctly point out our eyes are insensitive to red light so the red light will have a moderate output if we measured it with a photo sensor that was equally sensitive to all wavelengths.

Note it is only the light we can see that effects our dark adaptation. An IR "light" that could be very intense and appear very "bright" to an IR camera will not effect our dark adaptation at all. Conversely because are eyes are sensitive to green a light with a very low output( measured it with a photo sensor that was equally sensitive to all wavelengths) will effect our dark adaptation a lot.

Its how bright the light appears to a human observer (this is how we define brightness) that effects dark adaptation.

[zeehag]

my formosa came with a dim yellow light oriental lamp that worked just perfectly for this exact problem. i found, even with my bad visual accommodation, that i could see readily in the dark and still get around and find what i needed in my boat without ruination of night vision. i even placed a cloth napkin on top to prevent any glare, and was able to see just fine inside boat as well as outside boat. the red light i bought especially for that job failed drastically as i wasnt able to see what i sought in the cabin while using it.
white lights do not help anything-- they hurt.

[noelex 77]

Originally Posted by GordMay

Extremely dim light of any colour will preserve night vision (scotopic vision), since that what night vision is for - for seeing in extremely dim light. At these EXTREMELY dim levels, blue-green is the light wavelength we are most sensitive to, and therefore can be used at lower intensity levels than any other extremely dim colour.

Red light preserves night vision, at a higher intensity level than any other colour, since the dim light elements of the eye (rods) are insensitive to red light. This allows you to operate more effectively with red light, as a result of the greater light intensity possible, and therefore more detailed perception of the environment by the red-sensitive elements, of the eye without disrupting your night adaptation.

That is all correct as usual Gord.
It is worth pointing out , however, that a green light has be so dim( to fully preserve all our night vision) that we would not be able to see any detail at all. No reading numbers and figures. In fact it has to so dim we would not be able to tell what colour it was.
Red light can be bright enough that we can read numbers and letters and still preserve our night vision. This is because or night vision (scotopic vision) is very insensitive to red. We can use our photopic vision to see detail with red light and leave our scotopic vision unaffected.

[zeehag]

ok, so, if red light is sooooo great, please splain to those olde phartes with cataracts exactly why they cannot see using red light whereas they CAN see using a faint yellowish light...
enquiring mineds wanna know.......

[noelex 77]

Originally Posted by zeehag

ok, so, if red light is sooooo great, please splain to those olde phartes with cataracts exactly why they cannot see using red light whereas they CAN see using a faint yellowish light...
enquiring mineds wanna know.......

People with cataracts particularly nuclear cataract have a very yellow or yellow/ brown lens. This means that lens will only transmit these wavelengths

Monocromatic red light is difficult to use. All colour information is lost, the eye has chromatic aberration which makes focusing difficult with red light. Its uncomfortable, no one likes it.
Its not the light to use with vision problem but it is the best if you want to preserve night vision.

[zeehag]

my teensy weensy cataracts loved the yellowish light and were able to let my eyes see that which i needed to see without interfering with my accommodation to night -- i sailed 1500 miles this way and it worked. yes i read all the warnings and i was able to see in my 6000+ miles of gulf coast sailing that the white and green are confusable when trying tio discern them at entrance to tampa bay.
in pacific, which is ice 'n' dark, the yellowish glow was perfect. . had to use a flash lite to read by for charts, but the glow was perfect for running inside to fetch that which i needed--could actually SEE it, and then making the adjustment was not a problem, as none of my night vision was lost and i didnt have to try to get used to a different kind of vision.
surprised me as i didnt expect that to be the case.

[noelex 77]

Originally Posted by zeehag

my teensy weensy cataracts loved the yellowish light and were able to let my eyes see that which i needed to see without interfering with my accommodation to night -- i sailed 1500 miles this way and it worked. yes i read all the warnings and i was able to see in my 6000+ miles of gulf coast sailing that the white and green are confusable when trying tio discern them at entrance to tampa bay.
in pacific, which is ice 'n' dark, the yellowish glow was perfect. . had to use a flash lite to read by for charts, but the glow was perfect for running inside to fetch that which i needed--could actually SEE it, and then making the adjustment was not a problem, as none of my night vision was lost and i didnt have to try to get used to a different kind of vision.
surprised me as i didnt expect that to be the case.

Most boaters have never seen what full dark adaptation is like. Our modern world and our modern boats have too many light sources.
Next time you are on night sail away from shore lights, do me a favour Zeehag, turn off all light sources (other than your navigation lights). After 20 -30mins you will see what full dark adaptation looks like.
You can then decide if its worth taking steps to preserve night vision in the future.
If nothing else you will be amazed at the stars.