Can the use of a Sextant cause eye damage?

[hellosailor]

There's actually an easy home kludge to test IR filters. It turns out that common digital cameras, including cell phone cameras, and usually able to see IR. If you take any handy digital camera in video mode and point an infrared remote control at it, you should see a purplish flickering from the IR diode when you press buttons on the remote.

This gives you a way to actually SEE infrared.

Then you repeat the process, holding a suspected IR source up to the camera, or using a known IR source and moving a suspected IR filter in between the two. If the filter works--you won't see the purple flickering any more.

Note of course, even a digital camera can be damaged if you're taking direct picture of the run with it.

There's another way to test that can be found on YouTube. You can shine a suspected light source at a CD, using it as a diffraction grating, and measure the results of the light from it. I don't recall offhand if that's a UV or IR test, some folks do it to check green laser safety for unseen light.

[Cpt Pat]

Originally Posted by denverd0n

You can disagree with well-established scientific fact if you want, but I prefer to accept what is demonstrably true.


It is a fact that a white light, of the same luminosity as a red light, will affect your night vision to exactly the same degree. The main reason the myth of red lights exist is because red "night lights" are almost always of a low luminosity. People then compare these to white lights of a much higher luminosity, and come to the conclusion that the red light is better for night vision. No, it is the lower luminosity light that is better than the higher luminosity light. The color has nothing to do with it.

Please inform the US Air Force, US Navy, and aircraft manufacturers who all use red light to preserve night vision. There's a reason sub commanders call: "rig for red" before using an optical periscope.


The sleeping quarters in some vessels will use blue light instead because it still preserves some night vision and it doesn't shine through the eyelids of sleeping crew.

[Chuck Hawley]

May I suggest that you learn with a Davis Mk 15, 20, or 25? Generally available on eBay or other second-hand sites, they simulate a "real" sextant better than the Mk 3 (which is what I learned on, when I was about 12.)

Chuck Hawley

PS: More choices of shades, too.

[hellosailor]

Pat-
"Please inform the US Air Force, US Navy, and aircraft manufacturers who all use red light to preserve night vision. "
You've been misinformed.
Read into dtic.mil/dtic/tr/fulltext/u2/a273682.pdf which is an official USN document that discusses many aspects of colored lighting. And note, the USN actually required BLUE lighting in some sections of the nuclear submarines, going back as far as the 1980's.
There are many differing reasons and differing results for "night lighting" and there is absolutely nothing, besides Hollywood movies, that endorses or supports the old red vision standard all around.

This is pretty much like the advice every school child knows, that "Carrots give you better night vision." In point of fact, that's totally bogus. The lie was widely and heavily promoted by the Brits during WW2, who served their airmen large helpings of carrots while claiming this was to enhance their night vision. The truth was, this was a very successful disinformation campaign designed to make the Germans think that carrots were giving the Brits an advantage, while they were actually secretly using radar.

And here's a curve ball you won't see coming: Right now my favorite "night vision light" is a small UV-A LED penlight. It throws UV and near-UV light, visible to the eye as a dim purple glow. They're used for checking for urine stains, UV inks in currency, and other odd purposes. And until UV LEDs came on the market, not very portable at all.

But with a UV LED light, I can prowl around almost anywhere at night, leaving my full dark-adapted vision unaffected. But most things reflect or emit enough light in reaction to it, so that you're not "in the dark" at all.

[denverd0n]

Originally Posted by Cpt Pat

Please inform the US Air Force, US Navy, and aircraft manufacturers who all use red light to preserve night vision. There's a reason sub commanders call: "rig for red" before using an optical periscope.

I'm afraid your information is out of date. More than 30 years ago, in 1985, the navy published this paper:
http://www.dtic.mil/cgi-bin/GetTRDoc...c=GetTRDoc.pdf


They found no differences after adapting to either red or white light of equal brightness. Their conclusion was, "These results support the proposal to substitute low level white light for red light in submarine control rooms."


Look. Feel free to use red light at night if you want. It doesn't make any difference at all to me. If you feel better with red light, carry on.


But it IS a myth, and even the Navy has known that for 30 years now.

[Olddan1943]

Originally Posted by denverd0n

I'm afraid your information is out of date. More than 30 years ago, in 1985, the navy published this paper:
http://www.dtic.mil/cgi-bin/GetTRDoc...c=GetTRDoc.pdf


They found no differences after adapting to either red or white light of equal brightness. Their conclusion was, "These results support the proposal to substitute low level white light for red light in submarine control rooms."


Look. Feel free to use red light at night if you want. It doesn't make any difference at all to me. If you feel better with red light, carry on.


But it IS a myth, and even the Navy has known that for 30 years now.

Has it been that long since I sailed on submarines?
Can we at least agree the popular "blue lights" do nothing to preserve your night vision?

[denverd0n]

Originally Posted by Olddan1943

Has it been that long since I sailed on submarines?

I don't know, has it?


I would expect that, after coming to this conclusion in 1985, it probably took the Navy quite a few years to change out lights, and change their procedures. So, I would not be at all surprised to hear that there were still plenty of submarines using red lights well into the 90s.

[Olddan1943]

Originally Posted by denverd0n

I don't know, has it?


I would expect that, after coming to this conclusion in 1985, it probably took the Navy quite a few years to change out lights, and change their procedures. So, I would not be at all surprised to hear that there were still plenty of submarines using red lights well into the 90s.

I served on nuc subs in the 60s.
Daymn, that was a long long time ago.

[noelex 77]

Originally Posted by denverd0n

I'm afraid your information is out of date. More than 30 years ago, in 1985, the navy published this paper:
http://www.dtic.mil/cgi-bin/GetTRDoc...c=GetTRDoc.pdf

The study only looked at the first 10 seconds of dark adaptation. I can only assume the periscope is only used for a short time and the adaptation in this short period is important.

The background illumination was very low ( 0.09 fc or 0. 006 fc) . This is very dim and is the area where red and white light become more equal

The study makes the point:
“As is well known,exposure to red light results in faster dark adaptation once the light is turned off than does exposure to any other colour”

If you want to find a paper that supports the view that the colour of light makes no difference you need to stop them including pesky details such as the above .

[Cpt Pat]

Originally Posted by hellosailor

Pat-
"Please inform the US Air Force, US Navy, and aircraft manufacturers who all use red light to preserve night vision. "
You've been misinformed.
Read into dtic.mil/dtic/tr/fulltext/u2/a273682.pdf which is an official USN document that discusses many aspects of colored lighting. And note, the USN actually required BLUE lighting in some sections of the nuclear submarines, going back as far as the 1980's.
There are many differing reasons and differing results for "night lighting" and there is absolutely nothing, besides Hollywood movies, that endorses or supports the old red vision standard all around.

This is pretty much like the advice every school child knows, that "Carrots give you better night vision." In point of fact, that's totally bogus. The lie was widely and heavily promoted by the Brits during WW2, who served their airmen large helpings of carrots while claiming this was to enhance their night vision. The truth was, this was a very successful disinformation campaign designed to make the Germans think that carrots were giving the Brits an advantage, while they were actually secretly using radar.

And here's a curve ball you won't see coming: Right now my favorite "night vision light" is a small UV-A LED penlight. It throws UV and near-UV light, visible to the eye as a dim purple glow. They're used for checking for urine stains, UV inks in currency, and other odd purposes. And until UV LEDs came on the market, not very portable at all.

But with a UV LED light, I can prowl around almost anywhere at night, leaving my full dark-adapted vision unaffected. But most things reflect or emit enough light in reaction to it, so that you're not "in the dark" at all.

I suppose I have to change out all the red lights in my Cessna and every other airplane and helicopter I fly.

[thinwater]

Originally Posted by Time Theory

I was thinking of trying to learn Celestial Navigation and purchase a Davis MK 3 Sextant for practice. Do you know if using a Sextant properly over an extended period of time can cause permanent eye damage?

Do you think the Davis MK 3 provides adequate filters to protect the eyes?

Thank you for your help.

And if that is a concern... why do you want to use a sextant? Your GPS and backup GPS are going to fail, or the network is going to go down, during the 1-2 critical days of the few passages you will make to islands, that would have otherwise failed by using dead reckoning from the position where this failure occurred, and you are so far out that either asking directions or simply heading towards a large land mass is not an option? Your luck really sucks.



I'm sorry, but this is paranoia multiplied by paranoia. A synthetic problem. The odds of it happening in your lifetime are remote, and there will be a back-up plan most of the time anyway.


The same time would be better spent preping the boat against things that will actually be serious.

[Chuck Hawley]

Originally Posted by thinwater

The same time would be better spent preping the boat against things that will actually be serious.

I think that teaching yourself celestial navigation is a wonderful way to understand the order of the universe, and it's the closest that many atheists (myself included) will come to believing there is a Higher Power.

To be able to take some dusty tables, a $20 Casio watch, and a $50 plastic sextant, and to be able to find your position anywhere in the world is a very satisfying pursuit, and not necessarily related to one's paranoia. It's a beautiful thing, especially a three-star evening sight.

Chuck

[Singularity]

Originally Posted by Olddan1943

Can we at least agree the popular "blue lights" do nothing to preserve your night vision?

When you start looking at an environment/situation like a submarine, the decision to use blue light undoubtedly was at least partially influenced by blue light's effects on mood, cognition, creativity, sleep cycle, etc.

[Olddan1943]

Originally Posted by Singularity

When you start looking at an environment/situation like a submarine, the decision to use blue light undoubtedly was at least partially influenced by blue light's effects on mood, cognition, creativity, sleep cycle, etc.

That was in reference to all the boats that run with those blue lights.

[captmikem]

one thing to be aware of, if you are using the telescope (which most people do when shooting the sun), it is focusing the light to a pinpoint which is the retna of your eye. Like starting a fire with a lense, So it is extreamly important to throw in a strong filter before searching for the sun with the scope.

M