You're wrong about red lights not preserving your night vision...

by D
(Philadelphia)

Red lights DO preserve your night vision, this is no gimmick. I'll break it down for you:

We humans have a duplex retina, meaning we have two different types of photoreceptors: rods and cones. Rods and cones have specific functions that when used together, give us our vision.

Rods contribute to the magnocellular pathway, which attributes to our night vision as well as other things, but I'll stay focused. We do not have any rods in our central vision (that is why it's hard to see a dim star lit in the sky when you stare straight at it, but can see it better if you look off to the side of it). Rods absorb short wavelength light, such as blue and violet. So if you use a blue instrumentation panel, you will bleach your rods which will decrease your night vision.

Our cones are part of the parvocellular pathway and contribute to our color vision and acuity, but NOT NIGHT VISION. Our cones are sensitive to longer wavelengths of lights, such as red.

Colors are made up of differing wavelengths of light. Our cones see light from about 570nm to 700nm. Our rods view colors from 400nm-570nm. if you drop below the cone minimum, 570, we lose our color vision because our cones do not absorb light at these wavelengths. This is why when it's very dark outside or in a room, you can see someone but cannot tell what color something is.
If you move above 570nm, our rods no longer absorb the wavelength and only our cones do. By not having our rods bleached with light, our rods are able to stay alert for things like motion and night vision.

And finally to make my point.

Red light has a wavelength of around 650nm. This wavelength is too long to be absorbed by rods, but it will be absorbed by cones. So since your rods are not bleached, you HAVE BETTER NIGHT VISION. And because your cones are absorbing the red light, you can read the instrumentation panel!

We don't mind bleaching our cones because it only take 1.5mins for them to dark adapt. It takes our rods 40mins to dark adapt, so we don't want to bleach those.

"Bleaching" is that sudden brightness you get when you turn on the lights in a previously pitch dark room.


So there you have it! I hope I didn't put you too sleep with all of this, I just wanted you to have the correct information.
And you are not totally wrong in saying the intensity of the light contributes to night vision, but it's a fact that a dim red instrument panel will preserve your night vision better that a dim ______(insert any other color here)

And I know of of this because I'm in school to become an eye doctor :-D



Comments for You're wrong about red lights not preserving your night vision...

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Night Light
by: Mike

As you say Dave, most modern instruments have a soft rosy backlight.

So, as far as I’m concerned, the only extra lighting I use on deck is a very small torch and only use it if I drop something important (such as my cigarettes) in the cockpit.

I prefer to use paper charts, red light tends to affect how the colours on the chart appear so, at the chart table I use a dim white light but try to keep the time when it is on to a minimum.





What about a red head lamp ?
by: DAVE S

If the instrument panels are lit as they normally are (back-lit), will wearing a red head lamp help you see the panels and the environment outside the vessel?





Charts - vison at night in red light
by: Anonymous

Mike you are correct to suggest that red light will affect the colours you see on a chart.

However, that is covered by the chart, all objects that have colour also have specific shape or light frequency such as Red and Green Bouyage or Cardinal Marks.

Therefore with a good understanding of navigation, (not that common now days with electronic nav systems) we should be able to identfy an object by shape or light and at night we can differentiate between shade, to see the different colour bands.

It is safer to use red lights to preserve night vision to see the little fishing bouy that will snarl your prop.

Cheers

Paul






Navigator's Night Vision
by: Mike

Thank you D for passing on your expert knowledge.

I shall have to alter my ill-informed comments on red lights preserving night vision as being an old wives tale.

However, I still hold with the contention that a red filter will affect how we perceive the colours on a chart.

By chart I mean a paper chart, call me old fashioned if you wish but the paper chart has and always will be my main reference when navigating.

And it is particularly when approaching a strange harbour at night that one needs to both preserve ones night vision and be able to quickly verify what one is seeing with what is shown on the chart.

This is a situation that is often encountered when one is already tired from a day’s sailing.

The buoyage light marking the approach can be hard to pick out from all the other shore lights and one is also trying to keep an eye on the depth sounder, the compass, the GPS and watch for any other vessel’s lights.

Mike






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