One Very Underused Human Sense

[.Scott]

I thought of my experiences with night vision when I happened upon this essay (Into the Night).
To stay in best health, I do a two-hour, six mile walk every day. In the summer (when the days are hot) and the winter (when the days are very short), I often choose the night for this activity - and I never use a flashlight.

Here is how Cornell describes dark adaptation:

Humans (and most animals) can see in the “dark” only if there is some starlight or, better, moonlight. It takes some time (10 to 30 minutes) for your eyes to become dark adapted to see in such low-light conditions. Best conditions are on a night with no clouds and a full moon (try it!). When dark adapted, you can see only in black and white (no color). If there is no light at all – say in a deep cave – you cannot see anything.

Perhaps my night vision is better than most, but I do not entirely agree with this assessment. First, if my task is to walk dark streets on a moonless night, it only me takes 5 or 10 minutes to become fully functional. And on a cloudless night with a full moon, no dark adaptation is needed - unless you keep your home incredibly well lit. Of course, my night vision may be better than average - but my vision on whole is representative of my age (66) and well below average.

There is also this notion that human night vision is not up to snuff in comparison to many other animals - specifically those with retinas that feature a Tapetum Lucidum (TL). The TL retro-reflects light back through the retina giving the it a second chance to catch the photons. It is estimated to boost a cats light collecting power by 44%. I can't compare myself to a cat, but on occasions when I have walked a dog into the dusk, as darkness falls, the dog starts to strictly follow my lead - and if left without my direction, sits. And I would point this out: if my iris opens to a diameter that is at least 20% more than the dogs, I have at least that 44% advantage advertised for the TL.

Why not a flashlight? If you don't trust the terrain, you might need a flashlight (but try trusting the terrain - especially if it's a roadway). But for me, night vision is much superior. Flashlights create long pools of light that are limited in range and are usually very tunneling. And, of course, night vision is built it - so you won't forget to bring it along.

 

[BillTre]

Dogs of course can also enlarge their irises.
This can be fast. It is a neural feedback mechanism.

Dark adaptation is usually considered to involve the regeneration of rhodopsin which is broken down in bright light.
It is a slower cellular/biochemical event.

I used to work on ships and would occasionally stand watches as a lookout during dark hours.
It would take us about 20 minutes to develop good night vision.
We were mostly looking for small dim points of light far away (potential collisions).

We had red goggles to wear when we went into well lite parts of the ship so our rhodopsin would not get broken down again which would reduce our abilities to see in dim light.

 

[.Scott]

We had red goggles to wear when we went into well lite parts of the ship

When I worked for a company that put electronics onto computers, there were night modes that would limit the screens to red and black.

As a pilot, the cockpit would be lit in red - for the same reason. Guess what happened once when I used a red pen to fill out the planning sheet (navaids, radio frequencies, etc) for a night flight.

 

[berkeman]

Back when I used to hunt a lot, I'd often need to sneak into the hunting area in the dark an hour or two before dawn. I made a small 4-LED sneaker light with Red LEDs and a 9V battery. It worked great and I used it for years...