Could You Survive...Night Vision ©

 

 

During the late 70s and early 80s, the Spokane Daily Chronicle, printed a column in the Outdoors section, called “Could You Survive”, which was written by U.S. Air Force survival instructors.

 

No one sees as well at night, as they do during the day, but did you ever stop to think about why that was, or how you preserve your night vision when you are out in the wilderness?  Well, that is exactly what the authors of the “Could You Survive” article asked back on Tuesday, November 3, 1981, in the Spokane Daily Chronicle.

 

An excerpt from “Could You Survive” published in the Spokane Daily Chronicle, November 3, 1981.

So, what would you do?  Would you pick answer A, B ,C or D? 

 

“Hmmm, that’s a good question, isn’t it?  But first before we choose an answer, let’s talk about the anatomy of your eyes and about day vision versus night vision”.

 

The Mark-1 Eyeball

 

The anatomy of the eye, an excerpt from “Seeing at Night”, by Robert A. Alkov, PhD, from Fathom, Summer 1970, page 58.

Your eyes are like very sophisticated biological cameras, and certain parts of your eye resemble the parts of an analog camera, such as the lens which in a camera focuses light on to film and in a human eye focuses light onto the retina.  And your iris is like the diaphragm of the camera and opens or closes to regulate the amount of light entering your eye.

 

An excerpt from Scouting and Patrolling, MCWP 3-11.3, by the Marine Corp, Figure 5-1, showing how human eyes are like a simple camera.

Your retina, just like the film in an old-time camera, is a light sensitive layer made up of both cone cells and rod cells, which transmit a visual image to you brain when stimulated by light.  The center of the retina is a called the fovea centralis and contains only cone cells.  This part of retina is about 2 degrees wide, or about the width of your thumb, and at night is what is responsible for causing the “night blind spot” in the center of our visual field.  The rest of the retina is composed of both cone and rod cells, with rod cells becoming more common, until at the edges of the retina, there are only rod cells.  The “optic disk” is the spot in your eye where the optic nerves and blood vessels enter and leave your eye, and this is the spot that is responsible for causing the “day blind spot”.

 

An excerpt from “Oh Say, Can You See?”, by Major Nicholas E. Barreca, MD; from the U. S. Army Aviation Digest, June 1971, page 16.

Each cone cell contains a light and color sensitive pigment called iodopsin, which is not sensitive to any light below the level of full moonlight, and each single cone cell is connected by a single nerve to your brain.  Cone cells are what allow us to see in daylight, in color and in detail.  Rod cells contain a light sensitive pigment called rhodopsin, which is also called “visual purple”, and only distinguish shades of gray, black and white.  Many rod cells are connected in a series to a single nerve, and this is what allows low light to send a visual impulse to your brain. 

 

An excerpt from Rotary Wing Flight, FM 1-51, by U.S. Department of the Army, page 6-1.

Day Vision...Night Vision

 

There are three types of vision, phototropic, which allows you to see during the day, this type of vision only uses the cone cells of your retina; mesopic, that allows you to see during dusk and dawn, and which uses both the cone and rod cells of your retina; and scotopic, which is what allows you to see in the dark, and that only uses the rod cells of your retina.

 

Night, or dark adaptation, is the process by which your eyes adjust to seeing in low levels of light.  It involves both physiological and chemical changes in your eyes and it takes your rod cells about 30 to 45 minutes to produce enough rhodopsin,  or “visual purple” to increase rod cell sensitivity to light and allow your eyes to see in low light conditions.  Imagine entering a dark room, at first it is difficult to see anything.  Quickly however, your pupils dilate, or enlarge, to let in as much light as possible, and after about 5 to 10 minutes your cone cells become adjusted to the dim light and your eyes will be about 100 times more sensitive to light, than they were when you first entered the darkened room.  When fully adapted to the darkness of the room, your visual sensitivity to light is about 10,000 times higher than it was in a brightly lit area.  This process happens independently in both eyes and can be quickly lost if you are exposed to a bright, or even moderately bright light, which is why you should close one eye before being exposed to bright lights to prevent the total loss of your night vision.

 

Seeing at night...

 

An excerpt from the Flight Training Handbook.  Revised 1980, by the U. S. Flight Standards Service, page 194.

Scotopic vision or, night vision, is the type of vision we experience at night during conditions of partial moonlight or starlight.  At night your visual acuity drops from 20/20 to 20/400 and you will only be able to see large objects.  Also, you will be colorblind, because only your cone cells can detect color and at night only your rod cells are used.  Also, don’t forget that at night, you will experience a two-degree wide “night blind spot” in the center of your visual field, and you will have to rely on your peripheral vision to see, which means looking away from what you want to see!

 

An example of off-center viewing, from Long-Range Surveillance Unit Operations, FM 3-55.93, Figure J-2, page J-2.

During the day looking straight at something and using your central vision works, but not at night.  At night you must use your peripheral vision, because of the “night blind spot”,  This is called “off-center viewing”, and instead of looking directly at an object, you must look instead out of the corner of your eye, above, below, or to either side of what you want to see, just like in Figure J-2, above.  It varies from individual to individual, but experts recommend looking from 6^o to 15^o degrees away from what you want to see.  With your arm is fully extended out in front of you, this is between the width of three fingers (about 5^o) to one hand-span (or 15^o), which is the distance from the tip of your little finger to the tip of your index finger.

 

From “Measuring The Sky”, by Brian Ventrudo, April 19, 2009, HERE.  When fulling extending your arm, your fingers can measure degrees of distance.

At night, when using an off-center viewing, move your eyes in a series of short, systematic hops over and around what you are looking at.  This prevents “bleaching”, which is the neutralization of the rhodopsin in the rod cells.  When you use your rod cells, the visual purple in the individual rod cells “bleaches” or blacks out after 4 to 10 seconds and the object you are looking at will seem to fade and then disappear.  As the visual purple in the rod cells in one area bleaches out, you must shift your eyes slightly to use fresh rod cells.

 

Examples of scanning techniques for off-center viewing at night, an excerpt from Long-Range Surveillance Unit Operations, FM 3-55.93, Figure J-1, page J-2.

And the correct answer is...

 

An excerpt from “Could You Survive” published in the Spokane Daily Chronicle, November 3, 1981.

“So, what did you choose, did you choose D?  I hope so, but if not, now you know!”

 

The complete “Could You Survive” article, published in the Spokane Daily Chronicle, November 3, 1981, HERE.

Don’t forget to come back next week and read “Making an Altoids® Tin Spice Container ©”, where we will talk about spicing up that bland dehydrated food with an easy to make and carry Altoids® tin spice container.

 

I hope that you continue to enjoy The Woodsman’s Journal Online and look for me on YouTube at BandanaMan Productions for other related videos, HERE.  Don’t forget to follow me on both The Woodsman’s Journal Online, HERE, and subscribe to BandanaMan Productions on YouTube.  If you have questions, as always, feel free to leave a comment on either site.  I announce new articles on Facebook at Eric Reynolds, on Instagram at bandanamanaproductions, and on VK at Eric Reynolds, so watch for me.

 

That is all for now, and as always, until next time, Happy Trails!

 

Sources

 

 

Alkov, Robert A., PhD; “Seeing at Night”, Fathom, Volume 2, Summer 1970, pages 58-61, https://books.google.com/books?id=AN-8DgE5FWkC&pg=PP69&dq=night+vision+cigarette&hl=en&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwir0L39zsb5AhVeEGIAHdl9DZs4FBDoAXoECAQQAg#v=onepage&q=night%20vision%20cigarette&f=false, accessed August 15, 2022

 

Barreca, Major Nicholas E., MD; “Oh Say, Can You See?”, U. S. Army Aviation Digest, June 1971, pages 15 to 19, https://books.google.com/books?id=7x3z3yl2MvUC&pg=RA6-PA15&dq=%E2%80%9COh+Say,+Can+You+See?%E2%80%9D+%22figure+1%22&hl=en&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwjqxobl0dX5AhVTFlkFHbGbDzAQ6AF6BAgFEAI#v=onepage&q=%E2%80%9COh%20Say%2C%20Can%20You%20See%3F%E2%80%9D%20%22figure%201%22&f=false, accessed August 15, 2022

 

Marine Corp; Scouting and Patrolling, MCWP 3-11.3, [Department of the Navy, Headquarters United State Marine Corp, Washing ton DC, April 17, 2000], page 5-1, https://www.marines.mil/Portals/1/Publications/MCWP%203-11.3%20%20Scouting%20and%20Patrolling.pdf, accessed August 15, 2022,

 

Strauss, Lt. Col. Samuel, “Night Sight”, Flying Safety, Volume 46, April 1990, page 18, https://books.google.com/books?id=0IT9KouSWK8C&pg=RA3-PA19&dq=night+vision+cigarette&hl=en&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwjBqpr1x8b5AhXWGVkFHT7nCXIQ6AF6BAgDEAI#v=onepage&q=night%20vision%20cigarette&f=false, accessed August 15, 2022

 

U.S. Air Force Survival School, “Could You Survive”, Spokane Daily Chronicle, November 3, 1981, https://books.google.com/books?id=cwNMAAAAIBAJ&pg=PA10&dq=%22spokane+daily+chronicle%22+%22could+you+survive%22&article_id=4356,364873&hl=en&sa=X&ved=2ahUKEwjBnJTmzvTwAhXjGVkFHeaLBNoQ6AEwBnoECAMQAg#v=onepage&q=%22spokane%20daily%20chronicle%22%20%22could%20you%20survive%22&f=false, accessed August 9, 2022

 

U. S. Department of the Army, Long-Range Surveillance Unit Operations, FM 3-55.93, [Headquarters Department of the Army, Washington DC, June 2009], page J-2, https://www.globalsecurity.org/military/library/policy/army/fm/3-55-93/fm3-55-93.pdf, accessed August 15, 2022

 

U. S. Department of the Army, Rotary Wing Flight, FM 1-51, [Headquarters Department of the Army, Washington DC, April 16, 1979], page 6-1, https://books.google.com/books?id=KyAW48ANjZcC&pg=SA6-PA7&dq=night+vision+cigarette&hl=en&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwjBqpr1x8b5AhXWGVkFHT7nCXIQ6AF6BAgJEAI#v=onepage&q=night%20vision%20cigarette&f=false, accessed August 15, 2022

 

U. S. Flight Standards Service, Flight Training Handbook.  Revised 1980, [U.S. Dept. of Transportation, F.A.A., 1980 ], page 194, https://books.google.com/books?id=ioRTAAAAMAAJ&pg=PR11&dq=%E2%80%9Cflight+training+handbook%E2%80%9D+%224-1%22&hl=en&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwiBp_3P1dX5AhVIGVkFHaz3BssQ6AF6BAgEEAI#v=onepage&q=%E2%80%9Cflight%20training%20handbook%E2%80%9D%20%224-1%22&f=false, accessed August 15, 2022

 

Ventrudo, Brian; “Measuring The Sky”, April 19, 2009, https://oneminuteastronomer.com/860/measuring-sky/, accessed November 27, 2018