Red light at night is a MYTH?!??!

[wsmurdoch]

Originally Posted by noelex 77

The trick with far red light and why it has unique properties is that (in very simplified terms) it can be seen by cone receptors but not (or at least very little) by rod receptors. Thus far red light can be used by the cone system to read maps and instruments without bleaching out or effecting the rod system. Thus the dark adaptation of the rod system is retained. Other wavelengths cannot do this.

In Boy Scouts decades ago, we took pieces of paper in various colors all chosen to have about the same brightness in sunlight. We picked them guessing that in black and white they would all be the same shade of gray. Most striking was that at night under starlight when we could see no color, the medium blue paper looked white and the medium red paper looked black. Our night vision saw blue as white and red as black.

[sailingforfun]

For what it is worth, all airplane cockpits use red light. Given the risks involved in flying passengers I would like to think they have spent a lot of time and money researching this subject and determined red light is best for the pilots while flying at night.

[waterman46]

This subject came up before and was never really resolved in a scientific sense. You will hear from lot of folks quoting old studies or personal experience, but I want to do a controlled experiment where I use red light to find a minimum size print that I can read comfortably, then turn the light off and see if I can identify a distant shape in an almost dark room. Then do the same with white light. Both times looking for the minimum light and minimum shape size visible.

Using red and white lights to read print duplicates what you need to do if reading a paper chart. Then identification of shapes in the near dark will be a good test for remaining night vision as it would duplicate the kind of objects you need to see on a boat at night.

Just never got around to do this - now your post reminds me to try it. Need to figure out how to provide these controlled conditions at home.

[tkeithlu]

"I would like to think they have spent a lot of time and money researching this subject"

It's probably 1930s research. It was summarized in the Handbook of Experimental Psychology by the time I got there in the 1960s. It's Introductory Psychology "how the visual system works" stuff.

[tkeithlu]

You'll have a hard time finding a qualified researcher willing to spend all that time on a topic that was researched, very carefully, 80 years ago. It's perception, measured from the outside, and fits in a body of knowledge. When I lost track of this literature, in the mid 1970s, the research was at the photosensitive chemical level, including topics I glossed over in replying to the original poster. Your best bet, if you need to know more about it, would be to find a book on visual perception or maybe human factors engineering. If we had to start at the beginning with each generation of student, we'd never make any progress.

[Cadence]

I believe illumination of instrumentation with red light precludes the iris from closing down so that night vision is not inhibited after each glance.

[waterman46]

Originally Posted by redneckrob

I probably wasn't totally clear.
1. When they made cockpits NVG compatible they ripped out all red lights and replaced them with green. So all cockpit lighting in NVG compatible aircraft is green. You're never looking inside the cockpit on the goggles, its always under the goggles or with them off (they don't focus that close). So bottom line the aviation physiologists determined green cockpit lighting was fine instead of red for the cockpit at night.
2. The NVG tubes also happen to be green.
Doesn't matter why, what matters is that when you're hovering at night you're rapidly switching between glancing out through the goggles to looking under the goggles at the boat/swimmer/survivor that you're hovering over. So you've essentially got 2 big green lights 2" from your eyes and you're spending the majority of your time looking under them to the dark outside in order to hold your hover unaided (meaning not looking through the goggles). Which tells me that green light doesn't kill your night vision, given you're using it to hover using your unaided night vision despite 2 green light shining into your eyes that you're also looking directly into multiple times a minute.

It is amazing what rescuers can accomplish, just boggles my mind how they can hover like that - but I'm wondering if during the rescue hovering don't you have a very bright floodlight illuminating the scene? The scene lighting available might be quite a lot more than what is available to the crew on a boat trying to avoid an unlit bit of rocky land or a small unlit fishing boat with only starlight available.

[Adelie]

Night Vision - The Red Myth

[a64pilot]

Originally Posted by sailingforfun

For what it is worth, all airplane cockpits use red light. Given the risks involved in flying passengers I would like to think they have spent a lot of time and money researching this subject and determined red light is best for the pilots while flying at night.

Ones built in the 1970’s and earlier did. No newer aircraft that I know of does. Red light is a very persuasive idea and apparently still persists, but way too many studies have been done that have different results.
One problem with red light is it’s so far to one end of the spectrum that Older presbyopic folks can’t focus well with anything Red light lit so our visual acuity is seriously compromised, even kids have trouble just not as much.
Most newer aircraft don’t use steam gauges anyway, they have MPD’s which are actually a lot like plotter screens.
Personally I like old fashioned steam gauges, and in combat aircraft I used no light at all, almost every bit of data was displayed over my right eye in a helmet display unit, and anything I would need to see in the cockpit I used a “Lip light” which was a single blue green LED mounted on the microphone with a micro switch that you activated by poking your lip out, so no cockpit lights at all. You did “blind cockpit drills” until you knew exactly where every switch was and how it was selected, even a rotary switch, a very few needed to be looked at though, but they were few.

The best is no light at all, second best is a dim light that is only used when needed, and lastly is lights that are on all of the time and dimmed way down, worst is of course lights on all of the time and not dimmed, whatever the color is.
Of course don’t get so hung up on light discipline that you fall down the companionway steps and break your leg. So you do need to balance safety and need to see with light discipline

[rbrentp]

The scientific explanations are well covered, so here is a practical note: I put a dim red LED in my compass (obviously before reading the science here. Red was easy on my eyes but everything red in the compass disappeared. like all the major direction indicators. So while dim is good make sure that the faces of whatever you light will reflect the color you choose.

[a64pilot]

Originally Posted by rbrentp

The scientific explanations are well covered, so here is a practical note: I put a dim red LED in my compass (obviously before reading the science here. Red was easy on my eyes but everything red in the compass disappeared. like all the major direction indicators. So while dim is good make sure that the faces of whatever you light will reflect the color you choose.

Maps are very often the same, most anything dangerous is written in red, and all the danger notes disappear when lit with red light.

[hlev00]

Magenta is chosen specifically on charts because it remains visible under red light.

[Montanan]

FYI: Why wear an eye patch? Not to just look like a pirate, but so as to be able to see like a pirate.

If you keep one eye covered with an eye patch it will be protected from the night vision bleaching effect when exposed to a light source, such as your temporarily illuminating your navigation display, radar display, or a light turned on to read a chart. Or opening your refrigerator so as to get a cold one. Nota bene: Add an external switch so as to be able to disconnect the lamp inside your refrigerator so that when it is opened at night you don't have the sudden glare.

Then when you turn off the light source you can uncover the protected eye and utilize its comparatively enhanced night vision until your other eye that was exposed to light recovers its night vision which takes upwards of about 30 minutes to regain total acuity but regains most within 5 to 10 minutes.

Also the pirate eye patch can be stylistic so as to go with your Covid-19 face mask.

Arghhh!

[a64pilot]

With only one eye to see with, you lose depth perception. You can be trained to deal with that, anyone that flies an AH-64 goes through training so that they can.

[Montanan]

Originally Posted by a64pilot

Maps are very often the same, most anything dangerous is written in red, and all the danger notes disappear when lit with red light.

Originally Posted by hlev00

Magenta is chosen specifically on charts because it remains visible under red light.

Colors of objects

We usually view objects when they are illuminated by white light, usually sunlight or ordinary room light. White light is a mixture of all colors, in roughly equal proportions. White objects look white because they reflect back all the visible wavelengths of light that shine on them - so the light still looks white to us. Colored objects, on the other hand, reflect back only some of the wavelengths; the rest they absorb. For example, if white light shines on a red ball, the ball reflects back mostly red light, and so we see red. Most of the greens and blues that are part of white light are absorbed by the ball so we cannot see them. Likewise, a blue book is reflecting the blue part of the white light spectrum. The red and green parts are absorbed by the book.

What happens when red light shines on a red ball? It continues to reflect the red light, and so it is still red -- but a white ball would also look red in red light, because it reflects all colors. If instead we shine blue light on a red ball, it will look dark, because it does not reflect blue light. It cannot look red unless there is red light coming to it from the light source. And it cannot look blue because the red ball absorbs blue light. So when we ask what color an object is, the answer is not simple - it depends on what color light we are using to see the object.

One consequence of the fact that different colored objects absorb different wavelengths of light is that darker objects heat up faster in the sun than white ones do - because they absorb many of the different wavelengths of light energy, while white objects reflect most of the wavelengths.