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

[SailingAdrift]

In doing my research to find new LEDs for our refit it seems the general consensus is that red light doesn't really help night vision as I thought it did.

Basically it sounds light blue-green is best because it is more visible to the human eye at low intensity which is the real key to night vision retention/recovery... But a dimming white light is better than red, and the way I'm leaning.

Any thoughts I'd love to hear them.

[rslifkin]

Dim red is nicer to the eyes, but it depends on what you're trying to see. For some tasks, you can use a far dimmer white light to see adequately than you could with red light. In those cases, you'll recover faster from the dim white instead of the brighter red.

That becomes an issue for things like reading paper charts, especially where color definition matters. But if you just need to see enough to not trip over something or to see where your hands are and color doesn't matter, dim red should do the job.

[triibutu]

It's been my undestanding that red light is not really meant to light the surroundings and help you see in the dark like a flashlight would. Red light is used to e.g. check the map while hiking in the dark (moonlight), because red does not disturb the normal night vision as much as white light does.

[noelex 77]

Dull red light is difficult to use, but it is the only wavelength that can preserve the deepest levels of dark adaptation while still enabling some detail to be resolved.

[BigNut]

Originally Posted by noelex 77

Dull red light is difficult to use, but it is the only wavelength that can preserve the deepest levels of dark adaptation while still enabling some detail to be resolved.

Could you pass along some references fir this statement? I am very interested in this subject.

Thanks

[wsmurdoch]

https://www.cruisersforum.com/forums...ion-67713.html

[Kelkara]

Originally Posted by rslifkin

That becomes an issue for things like reading paper charts, especially where color definition matters.

This is an important issue when reading paper charts, the magenta ink all but disappears under red light ... and that magenta colour is used to mark lights, which is what you want to see at night.

[redneckrob]

We switched to all green lights in the cockpit for NVG compatibility. And of course the NVGs are green and when you hover on them you're looking under the goggles while they're still on to hover and back out through the goggles multiple times a minute without a huge impact on night vision. I'm pretty sure a whole bunch of aviation physiologists did a whole bunch of research before we and DoD spent a couple billion dollars retrofitting every cockpit for NVGs, at least I hope they did!

Ironically red light shows up brightest on NVGs because of the wavelength, you can see the red pair of a green and red flashing buoy gate literally miles further away. But because this whole red light thing is inculcated into the surface guys psyche, when they went to "darken ship" every night so the drug boats didn't see us they switched all red lights on. And subsequently lit the boat up like a Christmas tree to anyone using NVGs. At least it made it a bit easier for us to find them when we were returning from a night flight!

[tkeithlu]

OK. The issue of red light. You have two sets of visual receptors, generally called cones and rods after the approximate shapes of the photoreceptive cells themselves. The cones are not very sensitive - it takes more light to make them work, but they give you color vision plus detail since they are largely crowded into the fovea, on the center of your visual axis. While the cones are not very sensitive, it also takes bunch of light to overwhelm their chemical recycling; you only bleach your cones when snow blind or seeing an area of light gray due to looking at a welding arc or the sun. It takes time for this "after image" to fade as the photosensitive chemicals recycle and you start firing optic neurons again.

The issue is the other system, your rods. As you go about your day they are totally bleached out and insensitive. Walk into a dark theatre and it takes 20 minutes for them to become maximally active, at that point you can detect (if you are young) one or two photons. But, rods are not in your fovea, so your night vision is blurry, and if you are looking for a dim light it is best to look at the side of it - out in your fovea. It takes very little light to bleach rods. This vision has no color.

Then the red light. It is a wavelength that is not detected (no chemical reaction, no firing optic neurons, no bleaching) by rods. You can use a dim red light, using your cones to read a chart (magenta you will miss) without bleaching the rods that you carefully brought on line by staying in the dark for 20 minutes (Actually, you can use rods in about 7 minutes, just not at maximum sensitivity.)

Want to demonstrate some of this? Wake up in the dark, stumble to the bathroom, turn on the light, but keep one eye tightly shut. Return to bed, turn off the light, and open both eyes. You will be able to see in the very dim light with the eye you kept shut, but will be blind in the eye you exposed to the bathroom light. Feels wierd the first time you do it.

[letsgetsailing3]

So what's the answer, again?


Which color? Red or Green or Blue?

[Discovery 15797]

Originally Posted by SailingAdrift

In doing my research to find new LEDs for our refit it seems the general consensus is that red light doesn't really help night vision as I thought it did.

Basically it sounds light blue-green is best because it is more visible to the human eye at low intensity which is the real key to night vision retention/recovery... But a dimming white light is better than red, and the way I'm leaning.

Any thoughts I'd love to hear them.

There is a lot of science surrounding red vs blue vs green light effect on rods, cones, fovea, etc. Some of that 'science' is contradictory.

If you are inland, near coastal I really don't think it matters too much IMHO. Your eyes are being bombarded at night with lots of ambient light in the distance. Yes, you're going to reduce the intensity (backlighting) of chartplotters, radar, etc.

The real test is being offshore (> 25 miles from any land). I mistakenly installed a BlueSea USB charger with blue lighting on my switch console. At night that blue light (among the red lit switches) was like a flood light. In fact, it was so bad we first covered it up after the 2nd day, and by the 7th day I disconnected it. The backlighting (intensity) of equipment (chart-plotter, radar, etc) is also adjusted very low (lowest setting) at sea.

Red has the lowest 'energy' (long wavelength) compared to other lights. Intensity is a huge variable. Even a bright red light is worse than a muted blue or green light. The biggest downside to red is that you essentially become "color blind" at night. The greatest benefit it is that it 'feels softer' on the eyes for a longer period of time than lights of similar intensity.

[noelex 77]

Originally Posted by BigNut

Could you pass along some references fir this statement? I am very interested in this subject.

Thanks

This is a lecture on dark adaptation that is reasonably easy to understand:

https://www.slideshare.net/mobile/bo...ation-43148326

The effect of colour is covered by this diagram:

[tkeithlu]

Any color you see at night is relying on your cones, sitting at maximum sensitivity in the dark, because only the cone system sees color - including red. If you can keep the brightness,the area, and the time you spend looking at them minimal, you can use any color you like without bleaching out your rods.

Noelex, the dark adaption curve in the thumbnail appears to deal with the adaptation of three types of cone, not with the relative merits of rods versus cones. That graph would have two curves of similar shape, with the rod curve intesecting the cone curve at about seven minutes.

[SailingAdrift]

Based on my minutes of research, it sounds like the ideal color is green blue, but the real key to maintaining night vision is to use as dim as a source of light for as short a period of time as possible.

Basically, in lieu of adding a bunch of red lights, we're going to go the dressing in layers route and have dimmers where appropriate, but for the most part just use extra switches to make lighting extra scalable.

You can also go the old pirate way of wearing an eyepatch and switching back and forth ��

[noelex 77]

Originally Posted by tkeithlu

Then the red light. It is a wavelength that is not detected (no chemical reaction, no firing optic neurons, no bleaching) by rods. You can use a dim red light, using your cones to read a chart (magenta you will miss) without bleaching the rods

Good post.

The key to understanding why red light has advantages is summarised above. Red light enables you to use cones (which is the only system that can see enough detail to for example read a map) without bleaching out the rod system. Or rods provide the best vision in extremely dark conditions.